ovl: fix recursive oi->lock in ovl_link()

linking a non-copied-up file into a non-copied-up parent results in a
nested call to mutex_lock_interruptible(&oi->lock). Fix this by copying up
target parent before ovl_nlink_start(), same as done in ovl_rename().

~/unionmount-testsuite$ ./run --ov -s
~/unionmount-testsuite$ ln /mnt/a/foo100 /mnt/a/dir100/

 WARNING: possible recursive locking detected
 --------------------------------------------
 ln/1545 is trying to acquire lock:
 00000000bcce7c4c (&ovl_i_lock_key[depth]){+.+.}, at:
     ovl_copy_up_start+0x28/0x7d
 but task is already holding lock:
 0000000026d73d5b (&ovl_i_lock_key[depth]){+.+.}, at:
     ovl_nlink_start+0x3c/0xc1

[SzM: this seems to be a false positive, but doing the copy-up first is
harmless and removes the lockdep splat]

Reported-by: syzbot+3ef5c0d1a5cb0b21e6be@syzkaller.appspotmail.com
Fixes: 5f8415d6b87e ("ovl: persistent overlay inode nlink for...")
Cc: <stable@vger.kernel.org> # v4.13
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 276914a..e1a55ec 100644 (file)
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -663,6 +663,10 @@ static int ovl_link(struct dentry *old, struct inode *newdir,
        if (err)
                goto out_drop_write;
 
+       err = ovl_copy_up(new->d_parent);
+       if (err)
+               goto out_drop_write;
+
        if (ovl_is_metacopy_dentry(old)) {
                err = ovl_set_redirect(old, false);
                if (err)