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    Subject[PATCH 4.14 034/124] ovl: fix recursive oi->lock in ovl_link()
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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;

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