GFS2: Add kobject release method

This patch adds a kobject release function that properly maintains
the kobject use count, so that accesses to the sysfs files do not
cause an access to freed kernel memory after an unmount.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 24 insertions, 12 deletions

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index b8c250fc492..9b2389756ac 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -1118,20 +1118,33 @@ static int fill_super(struct super_block *sb, struct gfs2_args *args, int silent
 	}
 
 	error = init_names(sdp, silent);
-	if (error)
-		goto fail;
+	if (error) {
+		/* In this case, we haven't initialized sysfs, so we have to
+		   manually free the sdp. */
+		free_percpu(sdp->sd_lkstats);
+		kfree(sdp);
+		sb->s_fs_info = NULL;
+		return error;
+	}
 
 	snprintf(sdp->sd_fsname, GFS2_FSNAME_LEN, "%s", sdp->sd_table_name);
 
-	gfs2_create_debugfs_file(sdp);
-
 	error = gfs2_sys_fs_add(sdp);
+	/*
+	 * If we hit an error here, gfs2_sys_fs_add will have called function
+	 * kobject_put which causes the sysfs usage count to go to zero, which
+	 * causes sysfs to call function gfs2_sbd_release, which frees sdp.
+	 * Subsequent error paths here will call gfs2_sys_fs_del, which also
+	 * kobject_put to free sdp.
+	 */
 	if (error)
-		goto fail;
+		return error;
+
+	gfs2_create_debugfs_file(sdp);
 
 	error = gfs2_lm_mount(sdp, silent);
 	if (error)
-		goto fail_sys;
+		goto fail_debug;
 
 	error = init_locking(sdp, &mount_gh, DO);
 	if (error)
@@ -1215,12 +1228,12 @@ fail_locking:
 fail_lm:
 	gfs2_gl_hash_clear(sdp);
 	gfs2_lm_unmount(sdp);
-fail_sys:
-	gfs2_sys_fs_del(sdp);
-fail:
+fail_debug:
 	gfs2_delete_debugfs_file(sdp);
 	free_percpu(sdp->sd_lkstats);
-	kfree(sdp);
+	/* gfs2_sys_fs_del must be the last thing we do, since it causes
+	 * sysfs to call function gfs2_sbd_release, which frees sdp. */
+	gfs2_sys_fs_del(sdp);
 	sb->s_fs_info = NULL;
 	return error;
 }
@@ -1390,10 +1403,9 @@ static void gfs2_kill_sb(struct super_block *sb)
 	sdp->sd_root_dir = NULL;
 	sdp->sd_master_dir = NULL;
 	shrink_dcache_sb(sb);
-	kill_block_super(sb);
 	gfs2_delete_debugfs_file(sdp);
 	free_percpu(sdp->sd_lkstats);
-	kfree(sdp);
+	kill_block_super(sb);
 }
 
 struct file_system_type gfs2_fs_type = {