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pgsql: Fix incorrect sentinel byte logic in GenerationRealloc() 3+ messages / 1 participants [nested] [flat]
* pgsql: Fix incorrect sentinel byte logic in GenerationRealloc() @ 2024-07-06 01:59 David Rowley <drowley@postgresql.org> 0 siblings, 0 replies; 3+ messages in thread From: David Rowley @ 2024-07-06 01:59 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org 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 Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/97651b0139cfa511eaf063b60c900c2ba81b8ba2 Modified Files -------------- src/backend/utils/mmgr/generation.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) ^ permalink raw reply [nested|flat] 3+ messages in thread
* pgsql: Fix incorrect sentinel byte logic in GenerationRealloc() @ 2024-07-06 02:00 David Rowley <drowley@postgresql.org> 0 siblings, 0 replies; 3+ messages in thread From: David Rowley @ 2024-07-06 02:00 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org 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 Branch ------ REL_17_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/84a9d38006280f092b2b3f14841e4156c7a6e80d Modified Files -------------- src/backend/utils/mmgr/generation.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) ^ permalink raw reply [nested|flat] 3+ messages in thread
* pgsql: Fix incorrect sentinel byte logic in GenerationRealloc() @ 2024-07-06 02:00 David Rowley <drowley@postgresql.org> 0 siblings, 0 replies; 3+ messages in thread From: David Rowley @ 2024-07-06 02:00 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org 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 Branch ------ REL_16_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/49e29cbe8cbcb6bd4ac6c5dc64b1ad27844c1b5c Modified Files -------------- src/backend/utils/mmgr/generation.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) ^ permalink raw reply [nested|flat] 3+ messages in thread
end of thread, other threads:[~2024-07-06 02:00 UTC | newest] Thread overview: 3+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2024-07-06 01:59 pgsql: Fix incorrect sentinel byte logic in GenerationRealloc() David Rowley <drowley@postgresql.org> 2024-07-06 02:00 pgsql: Fix incorrect sentinel byte logic in GenerationRealloc() David Rowley <drowley@postgresql.org> 2024-07-06 02:00 pgsql: Fix incorrect sentinel byte logic in GenerationRealloc() David Rowley <drowley@postgresql.org>
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