Re: net: llc: NULL ptr deref in llc_ui_sendmsg

Sergei Shtylyov
2014-06-06T17:50:54Z

Hello.

On 06/06/2014 07:42 PM, Dave Jones 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) {

} else if (!llc->dev) {

> + rc = -ENODEV;
> + goto release;
> + }
> }
> hdrlen = llc->dev->hard_header_len + llc_ui_header_len(sk, addr);
> size = hdrlen + len;

WBR, Sergei