On Mon, Mar 29, 2021 at 06:49:07PM +0200, Mickaël Salaün wrote:
From: Mickaël Salaün mic@linux.microsoft.com
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.
Looks good to me. I realized that dentry leak will happen on underlying filesystem so unmount of underlying filesystem will give this warning. I created nested overlayfs configuration and could reproduce this error and tested that this patch fixes it.
Reviewed-by: Vivek Goyal vgoyal@redhat.com
Vivek
Cc: Amir Goldstein amir73il@gmail.com Cc: Miklos Szeredi miklos@szeredi.hu Cc: Vivek Goyal vgoyal@redhat.com Cc: stable@vger.kernel.org # v5.7+ Reported-by: syzbot syzkaller@googlegroups.com Fixes: 6815f479ca90 ("ovl: use only uppermetacopy state in ovl_lookup()") Signed-off-by: Mickaël Salaün mic@linux.microsoft.com Link: https://lore.kernel.org/r/20210329164907.2133175-1-mic@digikod.net
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