[PATCH v1] ovl: Fix leaked dentry

[Mickaël Salaün]

From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>

Since commit 6815f479ca90 ("ovl: use only uppermetacopy state in
ovl_lookup()"), overlayfs doesn't put temporary dentry when there is a
metacopy error, which leads to dentry leaks when shutting down the
related superblock:

  overlayfs: refusing to follow metacopy origin for (/file0)
  ...
  BUG: Dentry (____ptrval____){i=3f33,n=file3}  still in use (1) [unmount of overlay overlay]
  ...
  WARNING: CPU: 1 PID: 432 at umount_check.cold+0x107/0x14d
  CPU: 1 PID: 432 Comm: unmount-overlay Not tainted 5.12.0-rc5 #1
  ...
  RIP: 0010:umount_check.cold+0x107/0x14d
  ...
  Call Trace:
   d_walk+0x28c/0x950
   ? dentry_lru_isolate+0x2b0/0x2b0
   ? __kasan_slab_free+0x12/0x20
   do_one_tree+0x33/0x60
   shrink_dcache_for_umount+0x78/0x1d0
   generic_shutdown_super+0x70/0x440
   kill_anon_super+0x3e/0x70
   deactivate_locked_super+0xc4/0x160
   deactivate_super+0xfa/0x140
   cleanup_mnt+0x22e/0x370
   __cleanup_mnt+0x1a/0x30
   task_work_run+0x139/0x210
   do_exit+0xb0c/0x2820
   ? __kasan_check_read+0x1d/0x30
   ? find_held_lock+0x35/0x160
   ? lock_release+0x1b6/0x660
   ? mm_update_next_owner+0xa20/0xa20
   ? reacquire_held_locks+0x3f0/0x3f0
   ? __sanitizer_cov_trace_const_cmp4+0x22/0x30
   do_group_exit+0x135/0x380
   __do_sys_exit_group.isra.0+0x20/0x20
   __x64_sys_exit_group+0x3c/0x50
   do_syscall_64+0x45/0x70
   entry_SYSCALL_64_after_hwframe+0x44/0xae
  ...
  VFS: Busy inodes after unmount of overlay. Self-destruct in 5 seconds.  Have a nice day...

This fix has been tested with a syzkaller reproducer.

Cc: Amir Goldstein <amir73il@xxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v5.7+
Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Fixes: 6815f479ca90 ("ovl: use only uppermetacopy state in ovl_lookup()")
Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210329164907.2133175-1-mic@xxxxxxxxxxx
---
 fs/overlayfs/namei.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 3fe05fb5d145..424c594afd79 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -921,6 +921,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		if ((uppermetacopy || d.metacopy) && !ofs->config.metacopy) {
 			err = -EPERM;
 			pr_warn_ratelimited("refusing to follow metacopy origin for (%pd2)\n", dentry);
+			dput(this);
 			goto out_put;
 		}
 

base-commit: a5e13c6df0e41702d2b2c77c8ad41677ebb065b3
-- 
2.30.2