[PATCH AUTOSEL 5.9 125/147] gfs2: use-after-free in sysfs deregistration

Sasha Levin
2020-10-27T00:32:11Z

From: Jamie Iles <jamie@nuviainc.com>

[ Upstream commit c2a04b02c060c4858762edce4674d5cba3e5a96f ]

syzkaller found the following splat with CONFIG_DEBUG_KOBJECT_RELEASE=y:

Read of size 1 at addr ffff000028e896b8 by task kworker/1:2/228

CPU: 1 PID: 228 Comm: kworker/1:2 Tainted: G S 5.9.0-rc8+ #101
Hardware name: linux,dummy-virt (DT)
Workqueue: events kobject_delayed_cleanup
Call trace:
dump_backtrace+0x0/0x4d8
show_stack+0x34/0x48
dump_stack+0x174/0x1f8
print_address_description.constprop.0+0x5c/0x550
kasan_report+0x13c/0x1c0
__asan_report_load1_noabort+0x34/0x60
memcmp+0xd0/0xd8
gfs2_uevent+0xc4/0x188
kobject_uevent_env+0x54c/0x1240
kobject_uevent+0x2c/0x40
__kobject_del+0x190/0x1d8
kobject_delayed_cleanup+0x2bc/0x3b8
process_one_work+0x96c/0x18c0
worker_thread+0x3f0/0xc30
kthread+0x390/0x498
ret_from_fork+0x10/0x18

Allocated by task 1110:
kasan_save_stack+0x28/0x58
__kasan_kmalloc.isra.0+0xc8/0xe8
kasan_kmalloc+0x10/0x20
kmem_cache_alloc_trace+0x1d8/0x2f0
alloc_super+0x64/0x8c0
sget_fc+0x110/0x620
get_tree_bdev+0x190/0x648
gfs2_get_tree+0x50/0x228
vfs_get_tree+0x84/0x2e8
path_mount+0x1134/0x1da8
do_mount+0x124/0x138
__arm64_sys_mount+0x164/0x238
el0_svc_common.constprop.0+0x15c/0x598
do_el0_svc+0x60/0x150
el0_svc+0x34/0xb0
el0_sync_handler+0xc8/0x5b4
el0_sync+0x15c/0x180

Freed by task 228:
kasan_save_stack+0x28/0x58
kasan_set_track+0x28/0x40
kasan_set_free_info+0x24/0x48
__kasan_slab_free+0x118/0x190
kasan_slab_free+0x14/0x20
slab_free_freelist_hook+0x6c/0x210
kfree+0x13c/0x460

Use the same pattern as f2fs + ext4 where the kobject destruction must
complete before allowing the FS itself to be freed. This means that we
need an explicit free_sbd in the callers.

Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Jamie Iles <jamie@nuviainc.com>
[Also go to fail_free when init_names fails.]
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/gfs2/incore.h | 1 +
fs/gfs2/ops_fstype.c | 22 +++++-----------------
fs/gfs2/super.c | 1 +
fs/gfs2/sys.c | 5 ++++-
4 files changed, 11 insertions(+), 18 deletions(-)

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index ca2ec02436ec7..387e99d6eda9e 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -705,6 +705,7 @@ struct gfs2_sbd {
struct super_block *sd_vfs;
struct gfs2_pcpu_lkstats __percpu *sd_lkstats;
struct kobject sd_kobj;
+ struct completion sd_kobj_unregister;
unsigned long sd_flags; /* SDF_... */
struct gfs2_sb_host sd_sb;

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 6d18d2c91add2..5bd602a290f72 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -1062,26 +1062,14 @@ static int gfs2_fill_super(struct super_block *sb, struct fs_context *fc)
}

error = init_names(sdp, silent);
- if (error) {
- /* In this case, we haven't initialized sysfs, so we have to
- manually free the sdp. */
- free_sbd(sdp);
- sb->s_fs_info = NULL;
- return error;
- }
+ if (error)
+ goto fail_free;

snprintf(sdp->sd_fsname, sizeof(sdp->sd_fsname), "%s", sdp->sd_table_name);

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)
- return error;
+ goto fail_free;

gfs2_create_debugfs_file(sdp);

@@ -1179,9 +1167,9 @@ static int gfs2_fill_super(struct super_block *sb, struct fs_context *fc)
gfs2_lm_unmount(sdp);
fail_debug:
gfs2_delete_debugfs_file(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);
+fail_free:
+ free_sbd(sdp);
sb->s_fs_info = NULL;
return error;
}
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 9f4d9e7be8397..a28cf447b6b12 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -736,6 +736,7 @@ static void gfs2_put_super(struct super_block *sb)

/* At this point, we're through participating in the lockspace */
gfs2_sys_fs_del(sdp);
+ free_sbd(sdp);
}

/**
diff --git a/fs/gfs2/sys.c b/fs/gfs2/sys.c
index d28c41bd69b05..c3e72dba7418a 100644
--- a/fs/gfs2/sys.c
+++ b/fs/gfs2/sys.c
@@ -303,7 +303,7 @@ static void gfs2_sbd_release(struct kobject *kobj)
{
struct gfs2_sbd *sdp = container_of(kobj, struct gfs2_sbd, sd_kobj);

- free_sbd(sdp);
+ complete(&sdp->sd_kobj_unregister);
}

static struct kobj_type gfs2_ktype = {
@@ -655,6 +655,7 @@ int gfs2_sys_fs_add(struct gfs2_sbd *sdp)
sprintf(ro, "RDONLY=%d", sb_rdonly(sb));
sprintf(spectator, "SPECTATOR=%d", sdp->sd_args.ar_spectator ? 1 : 0);

+ init_completion(&sdp->sd_kobj_unregister);
sdp->sd_kobj.kset = gfs2_kset;
error = kobject_init_and_add(&sdp->sd_kobj, &gfs2_ktype, NULL,
"%s", sdp->sd_table_name);
@@ -685,6 +686,7 @@ int gfs2_sys_fs_add(struct gfs2_sbd *sdp)
fail_reg:
fs_err(sdp, "error %d adding sysfs files\n", error);
kobject_put(&sdp->sd_kobj);
+ wait_for_completion(&sdp->sd_kobj_unregister);
sb->s_fs_info = NULL;
return error;
}
@@ -695,6 +697,7 @@ void gfs2_sys_fs_del(struct gfs2_sbd *sdp)
sysfs_remove_group(&sdp->sd_kobj, &tune_group);
sysfs_remove_group(&sdp->sd_kobj, &lock_module_group);
kobject_put(&sdp->sd_kobj);
+ wait_for_completion(&sdp->sd_kobj_unregister);
}

static int gfs2_uevent(struct kset *kset, struct kobject *kobj,
--
2.25.1