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

... 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>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/namei.c b/fs/namei.c
index f624d132e01e..e30deefad8f8 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3273,6 +3273,10 @@ 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);