mirror of
https://github.com/nlohmann/json.git
synced 2026-09-07 00:37:58 +00:00
Stop CBOR indefinite-length strings from recursing per chunk
get_cbor_string() and get_cbor_binary() handled the indefinite-length forms (0x7F and 0x5F) by calling themselves once per chunk. Each chunk therefore cost a native stack frame, and since a chunk may itself be an indefinite- length string, an input of repeated 0x7F bytes reached one frame per input byte: 200,000 of them crash the process with SIGSEGV before a single byte is rejected. This is the same defect as #5104, in a path the container-level work does not touch. Count the open levels instead of recursing through them. That is enough here because every chunk is appended to the same result -- get_bytes() writes at result.size() -- so there is no per-level state to keep. The temporary chunk string and its copy into the result go away with the recursion. The definite-length cases move to get_cbor_string_chunk() and get_cbor_binary_chunk() unchanged, including their error messages, which still name 0x7F and 0x5F because those are handled one level up. Behaviour is unchanged. Comparing against develop over the interesting byte sequences -- empty, single-chunk, nested, over-closed and truncated forms, both strings and byte arrays, and an indefinite-length map key -- produces identical values, error codes, messages and byte offsets. The 200,000-level input now reports parse_error.110 at byte 200001 instead of crashing. Note that nesting these is not valid CBOR: RFC 8949, Section 3.2.3 forbids it. This does not change that either way -- it has always been accepted, and rejecting it is a separate decision (#5317, #5325). Should it be rejected later, that is now one condition on the level counter rather than a change to the control flow. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
@@ -996,23 +996,21 @@ class binary_reader
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}
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/*!
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@brief reads a CBOR string
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@brief reads a definite-length CBOR string
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This function first reads starting bytes to determine the expected
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string length and then copies this number of bytes into a string.
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Additionally, CBOR's strings with indefinite lengths are supported.
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Reads everything @ref get_cbor_string accepts except the indefinite-length
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form, which that function handles itself. The bytes are appended to @a
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result, so consecutive chunks of an indefinite-length string can be read
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into the same string.
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@param[out] result created string
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@param[out] result string the bytes are appended to
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@return whether string creation completed
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*/
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bool get_cbor_string(string_t& result)
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{
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if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "string")))
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{
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return false;
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}
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@pre @a current is not EOF
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*/
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bool get_cbor_string_chunk(string_t& result)
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{
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switch (current)
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{
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// UTF-8 string (0x00..0x17 bytes follow)
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@@ -1068,20 +1066,6 @@ class binary_reader
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return get_number(input_format_t::cbor, len) && get_string(input_format_t::cbor, len, result);
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}
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case 0x7F: // UTF-8 string (indefinite length)
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{
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while (get() != 0xFF)
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{
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string_t chunk;
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if (!get_cbor_string(chunk))
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{
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return false;
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}
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result.append(chunk);
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}
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return true;
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}
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default:
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{
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auto last_token = get_token_string();
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@@ -1092,23 +1076,82 @@ class binary_reader
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}
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/*!
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@brief reads a CBOR byte array
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@brief reads a CBOR string
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This function first reads starting bytes to determine the expected
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byte array length and then copies this number of bytes into the byte array.
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Additionally, CBOR's byte arrays with indefinite lengths are supported.
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string length and then copies this number of bytes into a string.
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Additionally, CBOR's strings with indefinite lengths are supported.
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@param[out] result created byte array
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@param[out] result created string
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@return whether string creation completed
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*/
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bool get_cbor_string(string_t& result)
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{
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// number of indefinite-length strings that have been opened and not
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// closed yet. RFC 8949, Section 3.2.3 does not permit nesting them,
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// but this reader has always accepted it, so the open levels are
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// counted instead of recursed through, which overflowed the stack for
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// an input of repeated 0x7F bytes (see #5104). Every chunk is appended
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// to the same result, so no per-level state is needed.
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std::size_t open = 0;
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while (true)
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{
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if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "string")))
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{
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return false;
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}
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if (current == 0x7F) // UTF-8 string (indefinite length)
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{
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++open;
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get();
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continue;
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}
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// a break marker closes the innermost indefinite-length string;
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// outside of one it is not a string and falls through to the error
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if (open != 0 && current == 0xFF)
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{
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if (--open == 0)
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{
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return true;
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}
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get();
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continue;
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}
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if (JSON_HEDLEY_UNLIKELY(!get_cbor_string_chunk(result)))
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{
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return false;
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}
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if (open == 0)
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{
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return true;
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}
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get();
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}
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}
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/*!
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@brief reads a definite-length CBOR byte array
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Reads everything @ref get_cbor_binary accepts except the indefinite-length
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form, which that function handles itself. The bytes are appended to @a
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result, so consecutive chunks of an indefinite-length byte array can be
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read into the same byte array.
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@param[out] result byte array the bytes are appended to
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@return whether byte array creation completed
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*/
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bool get_cbor_binary(binary_t& result)
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{
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if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "binary")))
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{
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return false;
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}
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@pre @a current is not EOF
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*/
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bool get_cbor_binary_chunk(binary_t& result)
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{
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switch (current)
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{
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// Binary data (0x00..0x17 bytes follow)
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@@ -1168,20 +1211,6 @@ class binary_reader
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get_binary(input_format_t::cbor, len, result);
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}
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case 0x5F: // Binary data (indefinite length)
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{
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while (get() != 0xFF)
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{
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binary_t chunk;
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if (!get_cbor_binary(chunk))
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{
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return false;
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}
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result.insert(result.end(), chunk.begin(), chunk.end());
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}
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return true;
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}
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default:
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{
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auto last_token = get_token_string();
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@@ -1191,6 +1220,63 @@ class binary_reader
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}
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}
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/*!
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@brief reads a CBOR byte array
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This function first reads starting bytes to determine the expected
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byte array length and then copies this number of bytes into the byte array.
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Additionally, CBOR's byte arrays with indefinite lengths are supported.
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@param[out] result created byte array
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@return whether byte array creation completed
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*/
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bool get_cbor_binary(binary_t& result)
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{
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// the open indefinite-length byte arrays are counted rather than
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// recursed through, for the reason given in @ref get_cbor_string
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std::size_t open = 0;
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while (true)
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{
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if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "binary")))
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{
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return false;
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}
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if (current == 0x5F) // Binary data (indefinite length)
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{
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++open;
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get();
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continue;
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}
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// a break marker closes the innermost indefinite-length byte
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// array; outside of one it falls through to the error below
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if (open != 0 && current == 0xFF)
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{
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if (--open == 0)
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{
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return true;
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}
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get();
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continue;
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}
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if (JSON_HEDLEY_UNLIKELY(!get_cbor_binary_chunk(result)))
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{
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return false;
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}
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if (open == 0)
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{
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return true;
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}
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get();
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}
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}
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/*!
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@brief narrow a definite CBOR array/map length to std::size_t
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@@ -11683,23 +11683,21 @@ class binary_reader
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}
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/*!
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@brief reads a CBOR string
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@brief reads a definite-length CBOR string
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This function first reads starting bytes to determine the expected
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string length and then copies this number of bytes into a string.
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Additionally, CBOR's strings with indefinite lengths are supported.
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Reads everything @ref get_cbor_string accepts except the indefinite-length
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form, which that function handles itself. The bytes are appended to @a
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result, so consecutive chunks of an indefinite-length string can be read
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into the same string.
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@param[out] result created string
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@param[out] result string the bytes are appended to
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@return whether string creation completed
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*/
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bool get_cbor_string(string_t& result)
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{
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if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "string")))
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{
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return false;
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}
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@pre @a current is not EOF
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*/
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bool get_cbor_string_chunk(string_t& result)
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{
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switch (current)
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{
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// UTF-8 string (0x00..0x17 bytes follow)
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@@ -11755,20 +11753,6 @@ class binary_reader
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return get_number(input_format_t::cbor, len) && get_string(input_format_t::cbor, len, result);
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}
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case 0x7F: // UTF-8 string (indefinite length)
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{
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while (get() != 0xFF)
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{
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string_t chunk;
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if (!get_cbor_string(chunk))
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{
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return false;
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}
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result.append(chunk);
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}
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return true;
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}
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default:
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{
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auto last_token = get_token_string();
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@@ -11779,23 +11763,82 @@ class binary_reader
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}
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/*!
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@brief reads a CBOR byte array
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@brief reads a CBOR string
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This function first reads starting bytes to determine the expected
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byte array length and then copies this number of bytes into the byte array.
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Additionally, CBOR's byte arrays with indefinite lengths are supported.
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string length and then copies this number of bytes into a string.
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Additionally, CBOR's strings with indefinite lengths are supported.
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@param[out] result created byte array
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@param[out] result created string
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@return whether string creation completed
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*/
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bool get_cbor_string(string_t& result)
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{
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// number of indefinite-length strings that have been opened and not
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// closed yet. RFC 8949, Section 3.2.3 does not permit nesting them,
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// but this reader has always accepted it, so the open levels are
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// counted instead of recursed through, which overflowed the stack for
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// an input of repeated 0x7F bytes (see #5104). Every chunk is appended
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// to the same result, so no per-level state is needed.
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std::size_t open = 0;
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while (true)
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{
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if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "string")))
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{
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return false;
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}
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if (current == 0x7F) // UTF-8 string (indefinite length)
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{
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++open;
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get();
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continue;
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}
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// a break marker closes the innermost indefinite-length string;
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// outside of one it is not a string and falls through to the error
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if (open != 0 && current == 0xFF)
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{
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if (--open == 0)
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{
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return true;
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}
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get();
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continue;
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}
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if (JSON_HEDLEY_UNLIKELY(!get_cbor_string_chunk(result)))
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{
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return false;
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}
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if (open == 0)
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{
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return true;
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}
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get();
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}
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}
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/*!
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@brief reads a definite-length CBOR byte array
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|
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Reads everything @ref get_cbor_binary accepts except the indefinite-length
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form, which that function handles itself. The bytes are appended to @a
|
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result, so consecutive chunks of an indefinite-length byte array can be
|
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read into the same byte array.
|
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|
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@param[out] result byte array the bytes are appended to
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@return whether byte array creation completed
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*/
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bool get_cbor_binary(binary_t& result)
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{
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if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "binary")))
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{
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return false;
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}
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@pre @a current is not EOF
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*/
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bool get_cbor_binary_chunk(binary_t& result)
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{
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switch (current)
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{
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// Binary data (0x00..0x17 bytes follow)
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@@ -11855,20 +11898,6 @@ class binary_reader
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get_binary(input_format_t::cbor, len, result);
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}
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case 0x5F: // Binary data (indefinite length)
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{
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while (get() != 0xFF)
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{
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binary_t chunk;
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if (!get_cbor_binary(chunk))
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{
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return false;
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}
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result.insert(result.end(), chunk.begin(), chunk.end());
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}
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return true;
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}
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default:
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{
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auto last_token = get_token_string();
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@@ -11878,6 +11907,63 @@ class binary_reader
|
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}
|
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}
|
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|
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/*!
|
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@brief reads a CBOR byte array
|
||||
|
||||
This function first reads starting bytes to determine the expected
|
||||
byte array length and then copies this number of bytes into the byte array.
|
||||
Additionally, CBOR's byte arrays with indefinite lengths are supported.
|
||||
|
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@param[out] result created byte array
|
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|
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@return whether byte array creation completed
|
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*/
|
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bool get_cbor_binary(binary_t& result)
|
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{
|
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// the open indefinite-length byte arrays are counted rather than
|
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// recursed through, for the reason given in @ref get_cbor_string
|
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std::size_t open = 0;
|
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|
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while (true)
|
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{
|
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if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::cbor, "binary")))
|
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{
|
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return false;
|
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}
|
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|
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if (current == 0x5F) // Binary data (indefinite length)
|
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{
|
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++open;
|
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get();
|
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continue;
|
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}
|
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|
||||
// a break marker closes the innermost indefinite-length byte
|
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// array; outside of one it falls through to the error below
|
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if (open != 0 && current == 0xFF)
|
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{
|
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if (--open == 0)
|
||||
{
|
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return true;
|
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}
|
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get();
|
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continue;
|
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}
|
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|
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if (JSON_HEDLEY_UNLIKELY(!get_cbor_binary_chunk(result)))
|
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{
|
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return false;
|
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}
|
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|
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if (open == 0)
|
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{
|
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return true;
|
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}
|
||||
|
||||
get();
|
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}
|
||||
}
|
||||
|
||||
/*!
|
||||
@brief narrow a definite CBOR array/map length to std::size_t
|
||||
|
||||
|
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@@ -2035,6 +2035,58 @@ TEST_CASE("CBOR definite length equal to the indefinite-length sentinel")
|
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}
|
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}
|
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TEST_CASE("CBOR indefinite-length strings do not recurse per chunk")
|
||||
{
|
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// Reading an indefinite-length string or byte array used to call itself
|
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// once per chunk, so a payload of repeated 0x7F (or 0x5F) bytes exhausted
|
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// the call stack before any of the input was rejected. The open levels are
|
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// counted now, and the levels below prove the reader still reads the same
|
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// values and reports the same errors at the same byte offsets.
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json _;
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|
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SECTION("many open levels are reported, not crashed on")
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{
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const std::vector<uint8_t> input(200000, 0x7F);
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CHECK_THROWS_WITH_AS(_ = json::from_cbor(input), "[json.exception.parse_error.110] parse error at byte 200001: syntax error while parsing CBOR string: unexpected end of input", json::parse_error&);
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CHECK(json::from_cbor(input, true, false).is_discarded());
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}
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SECTION("many open levels are reported, not crashed on (binary)")
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{
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const std::vector<uint8_t> input(200000, 0x5F);
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CHECK_THROWS_WITH_AS(_ = json::from_cbor(input), "[json.exception.parse_error.110] parse error at byte 200001: syntax error while parsing CBOR binary: unexpected end of input", json::parse_error&);
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CHECK(json::from_cbor(input, true, false).is_discarded());
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}
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SECTION("chunks are still concatenated")
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{
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CHECK(json::from_cbor(std::vector<uint8_t>({0x7F, 0xFF})) == json(""));
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CHECK(json::from_cbor(std::vector<uint8_t>({0x7F, 0x61, 0x61, 0xFF})) == json("a"));
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// nested indefinite-length strings are concatenated across levels
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CHECK(json::from_cbor(std::vector<uint8_t>({0x7F, 0x7F, 0x61, 0x61, 0xFF, 0x61, 0x62, 0xFF})) == json("ab"));
|
||||
CHECK(json::from_cbor(std::vector<uint8_t>({0x7F, 0x7F, 0x7F, 0x61, 0x7A, 0xFF, 0xFF, 0xFF})) == json("z"));
|
||||
CHECK(json::from_cbor(std::vector<uint8_t>({0xA1, 0x7F, 0x61, 0x61, 0xFF, 0x01})) == json({{"a", 1}}));
|
||||
}
|
||||
|
||||
SECTION("chunks are still concatenated (binary)")
|
||||
{
|
||||
CHECK(json::from_cbor(std::vector<uint8_t>({0x5F, 0x41, 0x61, 0xFF})) == json::binary({0x61}));
|
||||
CHECK(json::from_cbor(std::vector<uint8_t>({0x5F, 0x5F, 0x41, 0x61, 0xFF, 0x41, 0x62, 0xFF})) == json::binary({0x61, 0x62}));
|
||||
}
|
||||
|
||||
SECTION("a chunk that is not a string is still rejected")
|
||||
{
|
||||
CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0x7F, 0x7F, 0x00})), "[json.exception.parse_error.113] parse error at byte 3: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0x00", json::parse_error&);
|
||||
CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0x5F, 0x5F, 0x00})), "[json.exception.parse_error.113] parse error at byte 3: syntax error while parsing CBOR binary: expected length specification (0x40-0x5B) or indefinite binary array type (0x5F); last byte: 0x00", json::parse_error&);
|
||||
}
|
||||
|
||||
SECTION("a break marker outside an indefinite-length string is not a string")
|
||||
{
|
||||
// 0xFF only closes a string that was opened; on its own it is not one
|
||||
CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0xA1, 0xFF, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0xFF", json::parse_error&);
|
||||
}
|
||||
}
|
||||
|
||||
TEST_CASE("CBOR roundtrips" * doctest::skip())
|
||||
{
|
||||
SECTION("input from flynn")
|
||||
|
||||
Reference in New Issue
Block a user