do_last(): don't let a bogus return value from ->open() et.al. to confuse us

commit c80567c82ae4814a41287618e315a60ecf513be6 upstream.

... into returning a positive to path_openat(), which would interpret that
as "symlink had been encountered" and proceed to corrupt memory, etc.
It can only happen due to a bug in some ->open() instance or in some LSM
hook, etc., so we report any such event *and* make sure it doesn't trick
us into further unpleasantness.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/fs/namei.c b/fs/namei.c
index 8a0c3d9d8298f68e33f34a20e738becad42eb71b..34f8224be4edde051c3b1435a49dbf4cec1a03bd 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3108,6 +3108,10 @@ opened:
                        goto exit_fput;
        }
 out:
+       if (unlikely(error > 0)) {
+               WARN_ON(1);
+               error = -EINVAL;
+       }
        if (got_write)
                mnt_drop_write(nd->path.mnt);
        path_put(&save_parent);