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gh-148252: Fix stack depth calculation in binary reader on 32-bit platforms #148253

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gh-148252: Fix stack depth calculation in binary reader on 32-bit platforms #148253

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Security/2026-04-08-14-25-47.gh-issue-148252.IEp9Rt.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fixed stack depth calculation in :mod:`!_remote_debugging` when decoding
certain ``.pyb`` inputs on 32-bit builds. Issue originally identified and
diagnosed by Tristan Madani (@TristanInSec on GitHub).
32 changes: 20 additions & 12 deletions Modules/_remote_debugging/binary_io_reader.c
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Original file line number Diff line number Diff line change
Expand Up @@ -601,6 +601,20 @@ reader_get_or_create_thread_state(BinaryReader *reader, uint64_t thread_id,
* STACK DECODING HELPERS
* ============================================================================ */

/* Validate that final_depth fits in the stack buffer.
* Uses uint64_t to prevent overflow on 32-bit platforms. */
static inline int
validate_stack_depth(ReaderThreadState *ts, uint64_t final_depth)
{
if (final_depth > ts->current_stack_capacity) {
PyErr_Format(PyExc_ValueError,
"Final stack depth %llu exceeds capacity %zu",
(unsigned long long)final_depth, ts->current_stack_capacity);
return -1;
}
return 0;
}

/* Decode a full stack from sample data.
* Updates ts->current_stack and ts->current_stack_depth.
* Returns 0 on success, -1 on error (bounds violation). */
Expand Down Expand Up @@ -658,12 +672,9 @@ decode_stack_suffix(ReaderThreadState *ts, const uint8_t *data,
return -1;
}

/* Validate final depth doesn't exceed capacity */
size_t final_depth = (size_t)shared + new_count;
if (final_depth > ts->current_stack_capacity) {
PyErr_Format(PyExc_ValueError,
"Final stack depth %zu exceeds capacity %zu",
final_depth, ts->current_stack_capacity);
/* Use uint64_t to prevent overflow on 32-bit platforms */
uint64_t final_depth = (uint64_t)shared + new_count;
if (validate_stack_depth(ts, final_depth) < 0) {
return -1;
}

Expand Down Expand Up @@ -713,12 +724,9 @@ decode_stack_pop_push(ReaderThreadState *ts, const uint8_t *data,
}
size_t keep = (ts->current_stack_depth > pop) ? ts->current_stack_depth - pop : 0;

/* Validate final depth doesn't exceed capacity */
size_t final_depth = keep + push;
if (final_depth > ts->current_stack_capacity) {
PyErr_Format(PyExc_ValueError,
"Final stack depth %zu exceeds capacity %zu",
final_depth, ts->current_stack_capacity);
/* Use uint64_t to prevent overflow on 32-bit platforms */
uint64_t final_depth = (uint64_t)keep + push;
if (validate_stack_depth(ts, final_depth) < 0) {
return -1;
}

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