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

[ Upstream commit c80567c82ae4814a41287618e315a60ecf513be6 ]

... 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.

Cc: stable@vger.kernel.org # v3.6+, at least
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

diff --git a/fs/namei.c b/fs/namei.c
index be3d538d56b3a924fce28ed1b94710076090db5d..2a8ba683a888b9a6901987928fec8c17a11257e8 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3111,6 +3111,10 @@ static int do_last(struct nameidata *nd, struct path *path,
                        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);