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    Subject[PATCH 5.4 117/152] namei: only return -ECHILD from follow_dotdot_rcu()
    Date
    From: Aleksa Sarai <cyphar@cyphar.com>

    commit 2b98149c2377bff12be5dd3ce02ae0506e2dd613 upstream.

    It's over-zealous to return hard errors under RCU-walk here, given that
    a REF-walk will be triggered for all other cases handling ".." under
    RCU.

    The original purpose of this check was to ensure that if a rename occurs
    such that a directory is moved outside of the bind-mount which the
    resolution started in, it would be detected and blocked to avoid being
    able to mess with paths outside of the bind-mount. However, triggering a
    new REF-walk is just as effective a solution.

    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Fixes: 397d425dc26d ("vfs: Test for and handle paths that are unreachable from their mnt_root")
    Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/namei.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/fs/namei.c
    +++ b/fs/namei.c
    @@ -1360,7 +1360,7 @@ static int follow_dotdot_rcu(struct name
    nd->path.dentry = parent;
    nd->seq = seq;
    if (unlikely(!path_connected(&nd->path)))
    - return -ENOENT;
    + return -ECHILD;
    break;
    } else {
    struct mount *mnt = real_mount(nd->path.mnt);

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