[PATCH] xfs: If unable to pick perag an error needs to be returned

[Edward Adam Davis]

Syzbot reported a null-ptr-deref Write in xfs_filestream_select_ag.
When pag is not found, xfs_filestream_pick_ag() also returns 0, which leads
to null pointer access in xfs_filestream_create_association().

At the end of xfs_filestream_pick_ag, we need to add a sanity check for pag,
if we fail to grab any AG, we should return to -ENOSPC instead of 0.

Reported-and-tested-by: syzbot+4125a3c514e3436a02e6@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=4125a3c514e3436a02e6
Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
---
 fs/xfs/xfs_filestream.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c
index e3aaa0555597..dd8f193a3957 100644
--- a/fs/xfs/xfs_filestream.c
+++ b/fs/xfs/xfs_filestream.c
@@ -165,6 +165,10 @@ xfs_filestream_pick_ag(
 
 	trace_xfs_filestream_pick(pag, pino, free);
 	args->pag = pag;
+
+	if (!args->pag)
+		return -ENOSPC;
+
 	return 0;
 
 }
-- 
2.43.0