[PATCH 4.9 08/44] autofs: sanity check status reported with AUTOFS_DEV_IOCTL_FAIL

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: NeilBrown <neilb@suse.com>

commit 9fa4eb8e490a28de40964b1b0e583d8db4c7e57c upstream.

If a positive status is passed with the AUTOFS_DEV_IOCTL_FAIL ioctl,
autofs4_d_automount() will return

   ERR_PTR(status)

with that status to follow_automount(), which will then dereference an
invalid pointer.

So treat a positive status the same as zero, and map to ENOENT.

See comment in systemd src/core/automount.c::automount_send_ready().

Link: http://lkml.kernel.org/r/871sqwczx5.fsf@notabene.neil.brown.name
Signed-off-by: NeilBrown <neilb@suse.com>
Cc: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/autofs4/dev-ioctl.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/autofs4/dev-ioctl.c
+++ b/fs/autofs4/dev-ioctl.c
@@ -345,7 +345,7 @@ static int autofs_dev_ioctl_fail(struct
 	int status;
 
 	token = (autofs_wqt_t) param->fail.token;
-	status = param->fail.status ? param->fail.status : -ENOENT;
+	status = param->fail.status < 0 ? param->fail.status : -ENOENT;
 	return autofs4_wait_release(sbi, token, status);
 }