autofs: Fix automounts by using current_real_cred()->uid

Seth Forshee reports that in 4.8-rcN some automounts are failing
because the requesting the automount changed.

The relevant call path is:
follow_automount()
    ->d_automount
    autofs4_d_automount
       autofs4_mount_wait
           autofs4_wait

In autofs4_wait wq_uid and wq_gid are set to current_uid() and
current_gid respectively.  With follow_automount now overriding creds
uid that we export to userspace changes and that breaks existing
setups.

To remove the regression set wq_uid and wq_gid from
current_real_cred()->uid and current_real_cred()->gid respectively.
This restores the current behavior as current->real_cred is identical
to current->cred except when override creds are used.

Cc: stable@vger.kernel.org
Fixes: aeaa4a79ff6a ("fs: Call d_automount with the filesystems creds")
Reported-by: Seth Forshee <seth.forshee@canonical.com>
Tested-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
index 431fd7ee348864b01c231f89c3331c6c7c5ccb02..e44271dfceb6f8fd0740436d1754821914b7f9bf 100644 (file)
--- a/fs/autofs4/waitq.c
+++ b/fs/autofs4/waitq.c
@@ -431,8 +431,8 @@ int autofs4_wait(struct autofs_sb_info *sbi,
                memcpy(&wq->name, &qstr, sizeof(struct qstr));
                wq->dev = autofs4_get_dev(sbi);
                wq->ino = autofs4_get_ino(sbi);
-               wq->uid = current_uid();
-               wq->gid = current_gid();
+               wq->uid = current_real_cred()->uid;
+               wq->gid = current_real_cred()->gid;
                wq->pid = pid;
                wq->tgid = tgid;
                wq->status = -EINTR; /* Status return if interrupted */