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Make GetSnapshotData() more resilient on out-of-memory errors

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If the allocation of Snapshot->subxip fails, a follow-up call of
GetSnapshotData() would see a partially-initialized snapshot, causing a
NULL dereference on reentry when using "subxip" because only "xip" would
be allocated.  In the event of an out-of-memory error when allocating
"subxip", "xip" is now reset before throwing an ERROR, so as Snapshots
can be allocated and handled gracefully on retry.

This problem is unlikely going to show up in practice, so no backpatch.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Author: Matthias van de Meent <boekewurm+postgres@gmail.com>
Discussion: https://postgr.es/m/e77acaac-a1b3-40b3-99ee-5769b4e453e4@gmail.com
This commit is contained in:
Michael Paquier 2026-06-18 14:05:27 +09:00
parent bdae2c20e8
commit 29fb598b9c
1 changed files with 8 additions and 0 deletions
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8
src/backend/storage/ipc/procarray.c
View file

@ -2158,9 +2158,17 @@ GetSnapshotData(Snapshot snapshot)
snapshot->subxip = (TransactionId *)
malloc(GetMaxSnapshotSubxidCount() * sizeof(TransactionId));
if (snapshot->subxip == NULL)
{
/*
* Clean up the Snapshot state before throwing the error, so that
* a retry does not see a partially-initialized snapshot.
*/
free(snapshot->xip);
snapshot->xip = NULL;
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
errmsg("out of memory")));
}
}
/*