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Subject[PATCH 11/16] GFS2: Add kobject release method
Date
From: Bob Peterson <rpeterso@redhat.com>

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>

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index b8c250f..9b23897 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 9c2592b..e4bee4b 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;
}

--
1.7.4


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