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Fix possible NULL pointer dereference in GetNamedDSMSegment().

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GetNamedDSMSegment() doesn't check whether dsm_attach() returns
NULL, which creates the possibility of a NULL pointer dereference
soon after.  To fix, emit an ERROR if dsm_attach() returns NULL.
This shouldn't happen, but it would be nice to avoid a segfault if
it does.  In passing, tidy up the surrounding code.

Reported-by: Tom Lane
Reviewed-by: Michael Paquier, Bharath Rupireddy
Discussion: https://postgr.es/m/3348869.1705854106%40sss.pgh.pa.us
This commit is contained in:
Nathan Bossart 2024-01-22 20:44:38 -06:00
parent cdd863480c
commit 4372adfa24
1 changed files with 13 additions and 10 deletions
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23
src/backend/storage/ipc/dsm_registry.c
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@ -177,18 +177,21 @@ GetNamedDSMSegment(const char *name, size_t size,
(errmsg("requested DSM segment size does not match size of " (errmsg("requested DSM segment size does not match size of "
"existing segment"))); "existing segment")));
} }
else if (!dsm_find_mapping(entry->handle))
{
/* Attach to existing segment. */
dsm_segment *seg = dsm_attach(entry->handle);
dsm_pin_mapping(seg);
ret = dsm_segment_address(seg);
}
else else
{ {
/* Return address of an already-attached segment. */ dsm_segment *seg = dsm_find_mapping(entry->handle);
ret = dsm_segment_address(dsm_find_mapping(entry->handle));
/* If the existing segment is not already attached, attach it now. */
if (seg == NULL)
{
seg = dsm_attach(entry->handle);
if (seg == NULL)
elog(ERROR, "could not map dynamic shared memory segment");
dsm_pin_mapping(seg);
}
ret = dsm_segment_address(seg);
} }
dshash_release_lock(dsm_registry_table, entry); dshash_release_lock(dsm_registry_table, entry);