gfs2: Don't leave s_fs_info pointing to freed memory in init_sbd

commit 4c62bd9c upstream.

When alloc_percpu() fails, sdp gets freed but sb->s_fs_info still points
to the same address. Move the assignment after that error check so that
s_fs_info can only point to a valid sdp or NULL, which is checked for
later in the error path, in gfs2_kill_super().

Reported-by: syzbot+dcb8b3587445007f5808@syzkaller.appspotmail.com
Signed-off-by: Andrew Price <anprice@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/gfs2/ops_fstype.c

@@ -72,13 +72,13 @@ static struct gfs2_sbd *init_sbd(struct super_block *sb)
 	if (!sdp)
 		return NULL;
 
-	sb->s_fs_info = sdp;
 	sdp->sd_vfs = sb;
 	sdp->sd_lkstats = alloc_percpu(struct gfs2_pcpu_lkstats);
 	if (!sdp->sd_lkstats) {
 		kfree(sdp);
 		return NULL;
 	}
+	sb->s_fs_info = sdp;
 
 	set_bit(SDF_NOJOURNALID, &sdp->sd_flags);
 	gfs2_tune_init(&sdp->sd_tune);