Re: net: llc: NULL ptr deref in llc_ui_sendmsg

Dave Jones
2014-06-06T15:42:42Z

On Fri, Jun 06, 2014 at 11:08:33AM -0400, Sasha Levin wrote:
> Hi all,
>
> While fuzzing with trinity inside a KVM tools guest running the latest -next
> kernel I've stumbled on the following spew:
>
> [ 269.531162] BUG: unable to handle kernel NULL pointer dereference at 000000000000021e
> [ 269.531217] IP: llc_ui_sendmsg (net/llc/af_llc.c:912)

905 /* must bind connection to sap if user hasn't done it. */
906 if (sock_flag(sk, SOCK_ZAPPED)) {
907 /* bind to sap with null dev, exclusive. */
908 rc = llc_ui_autobind(sock, addr);
909 if (rc)
910 goto release;
911 }
912 hdrlen = llc->dev->hard_header_len + llc_ui_header_len(sk, addr);

looks like llc->dev was null, (understandable, given Trinity doesn't really know
how to set up llc beyond random socket()/setsockopt() calls).

llc_ui_autobind returns -ENODEV in that case, so it looks like the SOCK_ZAPPED test
was false. Something like the patch below maybe ? It feels ugly to be duplicating that
test there, but if this is agreed upon I'll resubmit this properly.

Dave

diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
index 0080d2b0a8ae..9b192db9883b 100644
--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -908,6 +908,11 @@ static int llc_ui_sendmsg(struct kiocb *iocb, struct socket *sock,
rc = llc_ui_autobind(sock, addr);
if (rc)
goto release;
+ } else {
+ if (!llc->dev) {
+ rc = -ENODEV;
+ goto release;
+ }
}
hdrlen = llc->dev->hard_header_len + llc_ui_header_len(sk, addr);
size = hdrlen + len;