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| author | David Rowley <drowley@postgresql.org> | 2024-07-06 14:00:06 +1200 |
|---|---|---|
| committer | David Rowley <drowley@postgresql.org> | 2024-07-06 14:00:06 +1200 |
| commit | 84a9d38006280f092b2b3f14841e4156c7a6e80d (patch) | |
| tree | 8246bea0a2b973cd8f5042005a5676fe796d3c9e /src/backend/utils | |
| parent | 9c273679b36b2c7c9ae13889ec6a5a3892842a6b (diff) | |
| download | postgresql-84a9d38006280f092b2b3f14841e4156c7a6e80d.tar.gz postgresql-84a9d38006280f092b2b3f14841e4156c7a6e80d.zip | |
Fix incorrect sentinel byte logic in GenerationRealloc()
This only affects MEMORY_CONTEXT_CHECKING builds.
This fixes an off-by-one issue in GenerationRealloc() where the
fast-path code which tries to reuse the existing allocation if the
existing chunk is >= the new requested size. The code there thought it
was always ok to use the existing chunk, but when oldsize == size there
isn't enough space to store the sentinel byte. If both sizes matched
exactly set_sentinel() would overwrite the first byte beyond the chunk
and then subsequent GenerationRealloc() calls could then fail the
Assert(chunk->requested_size < oldsize) check which is trying to ensure
the chunk is large enough to store the sentinel.
The same issue does not exist in aset.c as the sentinel checking code
only adds a sentinel byte if there's enough space in the chunk.
Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/49275921-7b39-41af-5eb8-97b50ce3312e@gmail.com
Backpatch-through: 16, where the problem was introduced by 0e480385e
Diffstat (limited to 'src/backend/utils')
| -rw-r--r-- | src/backend/utils/mmgr/generation.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c index b858b8d0f7b..0238c111d2f 100644 --- a/src/backend/utils/mmgr/generation.c +++ b/src/backend/utils/mmgr/generation.c @@ -846,8 +846,8 @@ GenerationRealloc(void *pointer, Size size, int flags) #endif /* - * Maybe the allocated area already is >= the new size. (In particular, - * we always fall out here if the requested size is a decrease.) + * Maybe the allocated area already big enough. (In particular, we always + * fall out here if the requested size is a decrease.) * * This memory context does not use power-of-2 chunk sizing and instead * carves the chunks to be as small as possible, so most repalloc() calls @@ -855,7 +855,12 @@ GenerationRealloc(void *pointer, Size size, int flags) * * XXX Perhaps we should annotate this condition with unlikely()? */ +#ifdef MEMORY_CONTEXT_CHECKING + /* With MEMORY_CONTEXT_CHECKING, we need an extra byte for the sentinel */ + if (oldsize > size) +#else if (oldsize >= size) +#endif { #ifdef MEMORY_CONTEXT_CHECKING Size oldrequest = chunk->requested_size; |