On Sun, Jan 21, 2024 at 11:21:46AM -0500, Tom Lane wrote:
> Coverity complained about this:
>
> *** CID 1586660: Null pointer dereferences (NULL_RETURNS)
> /srv/coverity/git/pgsql-git/postgresql/src/backend/storage/ipc/dsm_registry.c:
> 185 in GetNamedDSMSegment()
> 179 }
> 180 else if (!dsm_find_mapping(entry->handle))
> 181 {
> 182 /* Attach to existing segment. */
> 183 dsm_segment *seg = dsm_attach(entry->handle);
> 184
>>>> CID 1586660: Null pointer dereferences (NULL_RETURNS)
>>>> Dereferencing a pointer that might be "NULL" "seg" when calling
>>>> "dsm_pin_mapping".
> 185 dsm_pin_mapping(seg);
> 186 ret = dsm_segment_address(seg);
> 187 }
> 188 else
> 189 {
> 190 /* Return address of an already-attached segment. */
>
> I think it's right --- the comments for dsm_attach explicitly
> point out that a NULL return is possible. You need to handle
> that scenario in some way other than SIGSEGV.
Oops. I've attached an attempt at fixing this. I took the opportunity to
clean up the surrounding code a bit.
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
>From f4c1c7a7ce8bccf7251e384f895f34beb33f839e Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nat...@postgresql.org>
Date: Sun, 21 Jan 2024 16:05:16 -0600
Subject: [PATCH v1 1/1] fix coverity complaint
---
src/backend/storage/ipc/dsm_registry.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/src/backend/storage/ipc/dsm_registry.c b/src/backend/storage/ipc/dsm_registry.c
index ac11f51375..c178173653 100644
--- a/src/backend/storage/ipc/dsm_registry.c
+++ b/src/backend/storage/ipc/dsm_registry.c
@@ -177,19 +177,22 @@ GetNamedDSMSegment(const char *name, size_t size,
(errmsg("requested DSM segment size does not match size of "
"existing segment")));
}
- else if (!dsm_find_mapping(entry->handle))
+ else
{
- /* Attach to existing segment. */
- dsm_segment *seg = dsm_attach(entry->handle);
+ dsm_segment *seg = 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);
+ }
- dsm_pin_mapping(seg);
ret = dsm_segment_address(seg);
}
- else
- {
- /* Return address of an already-attached segment. */
- ret = dsm_segment_address(dsm_find_mapping(entry->handle));
- }
dshash_release_lock(dsm_registry_table, entry);
MemoryContextSwitchTo(oldcontext);
--
2.25.1
