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gh-148252: Avoid overflow in _remote_debugging binary reader bounds checks #148972

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gh-148252: Avoid overflow in _remote_debugging binary reader bounds checks #148972

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2ed6eb1
cannot be simpler?
maurycy Apr 24, 2026
3538dc3
blurb
maurycy Apr 24, 2026
70e11ce
gqgq
maurycy Apr 24, 2026
f14741f
SAMPLE_HEADER_FIXED_SIZE less magic
maurycy Apr 25, 2026
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Security/2026-04-24-23-15-42.gh-issue-148252.8BLmzd.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fixed string table and sample record bounds checks in :mod:`!_remote_debugging`
when decoding certain ``.pyb`` inputs on 32-bit builds. Patch by Maurycy
Pawłowski-Wieroński.
7 changes: 4 additions & 3 deletions Modules/_remote_debugging/binary_io_reader.c
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@

/* File structure sizes */
#define FILE_FOOTER_SIZE 32
#define SAMPLE_RECORD_HEADER_SIZE (sizeof(uint64_t) + sizeof(uint32_t) + 1)
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@maurycy maurycy Apr 24, 2026

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There's already SAMPLE_HEADER_FIXED_SIZE:

but it's hard-coded 13. Maybe it should be changed to this addition?

grep for 13 yields more results:

It looks that there's opportunity to move it to binary_io.h. Makes sense, @pablogsal ?

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@pablogsal pablogsal Apr 25, 2026

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I think it makes sense indeed 👍 Can you do the change in this PR?

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@maurycy maurycy Apr 25, 2026 •
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@pablogsal

Voilà: f14741f

Truth to be told, I think there's a massive room for improvement with consts here:

https://github.com/maurycy/cpython/blob/remote-debugging-int-bounds/Modules/_remote_debugging/binary_io_reader.c#L26
https://github.com/maurycy/cpython/blob/remote-debugging-int-bounds/Modules/_remote_debugging/binary_io_reader.c#L26

cpython/Modules/_remote_debugging/binary_io_reader.c

Line 33 in b2f126c

#define MAX_DECOMPRESS_SIZE (1ULL << 30)

cpython/Modules/_remote_debugging/binary_io_reader.c

Line 133 in b2f126c

#define MAX_DECOMPRESS_SIZE (1ULL << 30)

or magic offsets:

cpython/Modules/_remote_debugging/binary_io_writer.c

Lines 1146 to 1154 in b2f126c

uint64_t file_size = (uint64_t)footer_offset + 32;
uint8_t footer[32] = {0};
/* Cast size_t to uint32_t before memcpy to ensure correct bytes are copied
* on both little-endian and big-endian systems (size_t is 8 bytes on 64-bit) */
uint32_t string_count_u32 = (uint32_t)writer->string_count;
uint32_t frame_count_u32 = (uint32_t)writer->frame_count;
memcpy(footer + 0, &string_count_u32, 4);
memcpy(footer + 4, &frame_count_u32, 4);
memcpy(footer + 8, &file_size, 8);

(perhaps just FILE_FOOTER_SIZE here etc.)

https://github.com/maurycy/cpython/blob/f14741f422d0983f9a3c6a7bdd9c47b931e3fb1e/Modules/_remote_debugging/binary_io_reader.c#L985-L1003
https://github.com/maurycy/cpython/blob/f14741f422d0983f9a3c6a7bdd9c47b931e3fb1e/Modules/_remote_debugging/binary_io_writer.c#L651-L662
https://github.com/maurycy/cpython/blob/f14741f422d0983f9a3c6a7bdd9c47b931e3fb1e/Modules/_remote_debugging/binary_io_writer.c#L590-L595

(perhaps just SAMPLE_OFF warranted here as well)

etc., etc.

If interest in cleaning up these – I can create a PR.

#define MIN_DECOMPRESS_BUFFER_SIZE (64 * 1024) /* Minimum decompression buffer */

/* Progress callback frequency */
Expand Down Expand Up @@ -258,7 +259,7 @@ reader_parse_string_table(BinaryReader *reader, const uint8_t *data, size_t file
PyErr_SetString(PyExc_ValueError, "Malformed varint in string table");
return -1;
}
if (offset + str_len > file_size) {
if (offset > file_size || str_len > file_size - offset) {
PyErr_SetString(PyExc_ValueError, "String table overflow");
return -1;
}
Expand Down Expand Up @@ -976,8 +977,8 @@ binary_reader_replay(BinaryReader *reader, PyObject *collector, PyObject *progre
}

while (offset < reader->sample_data_size) {
/* Read thread_id (8 bytes) + interpreter_id (4 bytes) */
if (offset + 13 > reader->sample_data_size) {
/* Read thread_id (8 bytes) + interpreter_id (4 bytes) + encoding byte */
if (reader->sample_data_size - offset < SAMPLE_RECORD_HEADER_SIZE) {
break; /* End of data */
}

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