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>

2 files changed, 42 insertions, 15 deletions

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index b8c250fc4922..9b2389756acd 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 = {
diff --git a/fs/gfs2/sys.c b/fs/gfs2/sys.c
index 9c2592b1d5ff..e4bee4bebbf6 100644
--- a/fs/gfs2/sys.c
+++ b/fs/gfs2/sys.c
@@ -276,7 +276,15 @@ static struct attribute *gfs2_attrs[] = {
         NULL,
 };
 
+static void gfs2_sbd_release(struct kobject *kobj)
+{
+        struct gfs2_sbd *sdp = container_of(kobj, struct gfs2_sbd, sd_kobj);
+
+        kfree(sdp);
+}
+
 static struct kobj_type gfs2_ktype = {
+        .release = gfs2_sbd_release,
         .default_attrs = gfs2_attrs,
         .sysfs_ops     = &gfs2_attr_ops,
 };
@@ -583,6 +591,7 @@ int gfs2_sys_fs_add(struct gfs2_sbd *sdp)
         char ro[20];
         char spectator[20];
         char *envp[] = { ro, spectator, NULL };
+        int sysfs_frees_sdp = 0;
 
         sprintf(ro, "RDONLY=%d", (sb->s_flags & MS_RDONLY) ? 1 : 0);
         sprintf(spectator, "SPECTATOR=%d", sdp->sd_args.ar_spectator ? 1 : 0);
@@ -591,8 +600,10 @@ int gfs2_sys_fs_add(struct gfs2_sbd *sdp)
         error = kobject_init_and_add(&sdp->sd_kobj, &gfs2_ktype, NULL,
                                      "%s", sdp->sd_table_name);
         if (error)
-                goto fail;
+                goto fail_reg;
 
+        sysfs_frees_sdp = 1; /* Freeing sdp is now done by sysfs calling
+                                function gfs2_sbd_release. */
         error = sysfs_create_group(&sdp->sd_kobj, &tune_group);
         if (error)
                 goto fail_reg;
@@ -615,9 +626,13 @@ fail_lock_module:
 fail_tune:
         sysfs_remove_group(&sdp->sd_kobj, &tune_group);
 fail_reg:
-        kobject_put(&sdp->sd_kobj);
-fail:
+        free_percpu(sdp->sd_lkstats);
         fs_err(sdp, "error %d adding sysfs files", error);
+        if (sysfs_frees_sdp)
+                kobject_put(&sdp->sd_kobj);
+        else
+                kfree(sdp);
+        sb->s_fs_info = NULL;
         return error;
 }