[Devel] [PATCH rh7] overlayfs: fix dentry reference leak

[Maxim Patlasov]

Without this patch it is easy to crash node by fiddling
with overlayfs dirs. Backport commit ab79efab0 from ms:

From: David Howells <dhowells at redhat.com>

In ovl_copy_up_locked(), newdentry is leaked if the function exits through
out_cleanup as this just to out after calling ovl_cleanup() - which doesn't
actually release the ref on newdentry.

The out_cleanup segment should instead exit through out2 as certainly
newdentry leaks - and possibly upper does also, though this isn't caught
given the catch of newdentry.

Without this fix, something like the following is seen:

    BUG: Dentry ffff880023e9eb20{i=f861,n=#ffff880023e82d90} still in use (1) [unmount of tmpfs tmpfs]
    BUG: Dentry ffff880023ece640{i=0,n=bigfile}  still in use (1) [unmount of tmpfs tmpfs]

when unmounting the upper layer after an error occurred in copyup.

An error can be induced by creating a big file in a lower layer with
something like:

    dd if=/dev/zero of=/lower/a/bigfile bs=65536 count=1 seek=$((0xf000))

to create a large file (4.1G).  Overlay an upper layer that is too small
(on tmpfs might do) and then induce a copy up by opening it writably.

Reported-by: Ulrich Obergfell <uobergfe at redhat.com>
Signed-off-by: David Howells <dhowells at redhat.com>
Signed-off-by: Miklos Szeredi <miklos at szeredi.hu>

https://jira.sw.ru/browse/PSBM-47981
---
 fs/overlayfs/copy_up.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 3f3d1b0..afed35c 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -299,7 +299,7 @@ out:
 
 out_cleanup:
 	ovl_cleanup(wdir, newdentry);
-	goto out;
+	goto out2;
 }
 
 /*