On Mon, Mar 29, 2021 at 06:49:07PM +0200, Mickaël Salaün wrote:
> 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:
>
Hi,
Thanks for finding and fixing this bug. Patch looks correct to me. We
need to drop that reference to this.
I am not able to trigger this warning on umount of overlayfs. I copied
up a file with metacopy enabled and then remounted overlay again with
metacopy disabled. That does hit this code and I see the warning.
refusing to follow metacopy origin for (/foo.txt)
This should have lead to leak of dentry pointed by "this".
But after that I unmounted, overlay and that succeeds. Is there any
additional step to be done to trigger this VFS warning.
Vivek
> 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
>
