xfs: check _alloc_read_agf buffer pointer before using

Source kernel commit: 10479e2dea83d4c421ad05dfc55d918aa8dfc0cd

In some circumstances, _alloc_read_agf can return an error code of zero
but also a null AGF buffer pointer.  Check for this and jump out.

Fixes-coverity-id: 1415250
Fixes-coverity-id: 1415320
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>

diff --git a/libxfs/xfs_refcount.c b/libxfs/xfs_refcount.c
index 52ec20c74d6ddc5022cc56952811a39f54a48cba..3e0c815235da8980f5a062bbee333322d8e24595 100644 (file)
--- a/libxfs/xfs_refcount.c
+++ b/libxfs/xfs_refcount.c
@@ -1637,6 +1637,10 @@ xfs_refcount_recover_cow_leftovers(
        error = xfs_alloc_read_agf(mp, tp, agno, 0, &agbp);
        if (error)
                goto out_trans;
+       if (!agbp) {
+               error = -ENOMEM;
+               goto out_trans;
+       }
        cur = xfs_refcountbt_init_cursor(mp, tp, agbp, agno, NULL);
 
        /* Find all the leftover CoW staging extents. */