[PATCH 4.14 034/124] ovl: fix recursive oi->lock in ovl_link()

Greg Kroah-Hartman
2018-11-19T16:49:02Z

From: Amir Goldstein <amir73il@gmail.com>

commit 6cd078702f2f33cb6b19a682de3e9184112f1a46 upstream.

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>
[amir: backport to v4.18]
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/overlayfs/dir.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -595,6 +595,11 @@ static int ovl_link(struct dentry *old,
if (err)
goto out_drop_write;

+ err = ovl_copy_up(new->d_parent);
+ if (err)
+ goto out_drop_write;
+
+
err = ovl_nlink_start(old, &locked);
if (err)
goto out_drop_write;