Fix UB in allgather with zero-size output#495
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pavanbalaji wants to merge 1 commit intopytorch:mainfrom
Open
Fix UB in allgather with zero-size output#495pavanbalaji wants to merge 1 commit intopytorch:mainfrom
pavanbalaji wants to merge 1 commit intopytorch:mainfrom
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Summary: When the output buffer is empty (outBytes == 0), the input buffer pointer may be null. The memcpy at line 50 was called before the early return check, passing a null pointer to memcpy which is undefined behavior even with size 0. UBSAN catches this in the Count_0 test cases. Move the outBytes == 0 early return before the memcpy to avoid the null pointer. Split the context->size == 1 check to remain after the memcpy, since single-process still needs the input-to-output copy. Differential Revision: D95712700
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@pavanbalaji has exported this pull request. If you are a Meta employee, you can view the originating Diff in D95712700. |
| const size_t inBytes = out->size / context->size; | ||
| const size_t outBytes = out->size; | ||
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| // Short circuit if the output is empty. |
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will this be better before calculating sendRank & recvRank i.e under sanity checks?
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Summary:
When the output buffer is empty (outBytes == 0), the input
buffer pointer may be null. The memcpy at line 50 was called
before the early return check, passing a null pointer to
memcpy which is undefined behavior even with size 0. UBSAN
catches this in the Count_0 test cases.
Move the outBytes == 0 early return before the memcpy to
avoid the null pointer. Split the context->size == 1 check
to remain after the memcpy, since single-process still needs
the input-to-output copy.
Differential Revision: D95712700