[PATCH] NFSv4: Fix a NULL pointer dereference in pnfs_mark_matching_lsegs_return()

[schumaker.anna@gmail.com]

From: Anna Schumaker <Anna.Schumaker@Netapp.com>

Commit de144ff4234f changes _pnfs_return_layout() to call
pnfs_mark_matching_lsegs_return() passing NULL as the struct
pnfs_layout_range argument. Unfortunately,
pnfs_mark_matching_lsegs_return() doesn't check if we have a value here
before dereferencing it, causing an oops.

I'm able to hit this crash consistently when running connectathon basic
tests on NFS v4.1/v4.2 against Ontap.

Fixes: de144ff4234f ("NFSv4: Don't discard segments marked for return in _pnfs_return_layout()")
Cc: stable@vger.kernel.org
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
---
 fs/nfs/pnfs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index 03e0b34c4a64..6d720afb7b70 100644
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -2484,12 +2484,12 @@ pnfs_mark_matching_lsegs_return(struct pnfs_layout_hdr *lo,
 			set_bit(NFS_LSEG_LAYOUTRETURN, &lseg->pls_flags);
 		}
 
-	if (remaining) {
+	if (remaining && return_range) {
 		pnfs_set_plh_return_info(lo, return_range->iomode, seq);
 		return -EBUSY;
 	}
 
-	if (!list_empty(&lo->plh_return_segs)) {
+	if (return_range && !list_empty(&lo->plh_return_segs)) {
 		pnfs_set_plh_return_info(lo, return_range->iomode, seq);
 		return 0;
 	}
-- 
2.29.2