NotificationsYou must be signed in to change notification settings
Fork6
Star31

Commit84a9d38

committed

Fix incorrect sentinel byte logic in GenerationRealloc()

This only affects MEMORY_CONTEXT_CHECKING builds.This fixes an off-by-one issue in GenerationRealloc() where thefast-path code which tries to reuse the existing allocation if theexisting chunk is >= the new requested size. The code there thought itwas always ok to use the existing chunk, but when oldsize == size thereisn't enough space to store the sentinel byte. If both sizes matchedexactly set_sentinel() would overwrite the first byte beyond the chunkand then subsequent GenerationRealloc() calls could then fail theAssert(chunk->requested_size < oldsize) check which is trying to ensurethe chunk is large enough to store the sentinel.The same issue does not exist in aset.c as the sentinel checking codeonly 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.comBackpatch-through: 16, where the problem was introduced by0e48038

1 parent9c27367 commit84a9d38Copy full SHA for 84a9d38

File tree

1 file changed

-2

lines changed

src/backend/utils/mmgr
- generation.c

1 file changed

-2

lines changed

`‎src/backend/utils/mmgr/generation.c`

Lines changed: 7 additions & 2 deletions

Original file line number	Diff line number	Diff line change
`@@ -846,16 +846,21 @@ GenerationRealloc(void *pointer, Size size, int flags)`
`846`	`846`	`#endif`
`847`	`847`
`848`	`848`	`/*`
`849`		`- * Maybe the allocated area alreadyis >= the new size. (In particular,`
`850`		`- *we alwaysfall out here if the requested size is a decrease.)`
	`849`	`+ * Maybe the allocated area alreadybig enough. (In particular, we always`
	`850`	`+ * fall out here if the requested size is a decrease.)`
`851`	`851`	`*`
`852`	`852`	`* This memory context does not use power-of-2 chunk sizing and instead`
`853`	`853`	`* carves the chunks to be as small as possible, so most repalloc() calls`
`854`	`854`	`* will end up in the palloc/memcpy/pfree branch.`
`855`	`855`	`*`
`856`	`856`	`* XXX Perhaps we should annotate this condition with unlikely()?`
`857`	`857`	`*/`
	`858`	`+#ifdefMEMORY_CONTEXT_CHECKING`
	`859`	`+/* With MEMORY_CONTEXT_CHECKING, we need an extra byte for the sentinel */`
	`860`	`+if (oldsize>size)`
	`861`	`+#else`
`858`	`862`	`if (oldsize >=size)`
	`863`	`+#endif`
`859`	`864`	`{`
`860`	`865`	`#ifdefMEMORY_CONTEXT_CHECKING`
`861`	`866`	`Sizeoldrequest=chunk->requested_size;`

0 commit comments

Comments

(0)

Movatterモバイル変換

Navigation Menu

Search code, repositories, users, issues, pull requests...

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Commit84a9d38

File tree

1 file changed

1 file changed

`‎src/backend/utils/mmgr/generation.c`

0 commit comments