[GFS2] panic after can't parse mount arguments

When you try to mount gfs2 with -o garbage, the mount fails and the gfs2
superblock is deallocated and becomes NULL. The vfs comes around later
on and calls gfs2_kill_sb. At this point the hidden gfs2 superblock
pointer (sb->s_fs_info) is NULL and dereferencing it through
gfs2_meta_syncfs causes the panic. (the other function call to
gfs2_delete_debugfs_file() succeeds because this function already checks
for a NULL pointer)

Signed-off-by: Abhijith Das <adas@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 9e0e9be1e41d..314c1134d12d 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -887,8 +887,10 @@ error:
 
 static void gfs2_kill_sb(struct super_block *sb)
 {
-        gfs2_delete_debugfs_file(sb->s_fs_info);
-        gfs2_meta_syncfs(sb->s_fs_info);
+        if (sb->s_fs_info) {
+                gfs2_delete_debugfs_file(sb->s_fs_info);
+                gfs2_meta_syncfs(sb->s_fs_info);
+        }
         kill_block_super(sb);
 }