GFS2: Fix crash during ACL deletion in acl max entry check in gfs2_set_acl()

commit 27870207 upstream.

Fixes: e01580bf ("gfs2: use generic posix ACL infrastructure")
Reported-by: Eric Meddaugh <etmsys@rit.edu>
Tested-by: Eric Meddaugh <etmsys@rit.edu>
Signed-off-by: Andrew Elble <aweits@rit.edu>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

fs/gfs2/acl.c

@@ -73,7 +73,7 @@ int gfs2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 
 	BUG_ON(name == NULL);
 
-	if (acl->a_count > GFS2_ACL_MAX_ENTRIES(GFS2_SB(inode)))
+	if (acl && acl->a_count > GFS2_ACL_MAX_ENTRIES(GFS2_SB(inode)))
 		return -E2BIG;
 
 	if (type == ACL_TYPE_ACCESS) {