On Thu, 02 Jun 2022 12:38:10 +0200 Paolo Abeni wrote:
> I'm sorry for the multiple incremental feedback on this patch. It's
> somewhat tricky.
>
> AFAICS Jakub mentioned only udpv6_sendmsg(). In l2tp_ip6_sendmsg() we
> can have an overflow:
>
> int transhdrlen = 4; /* zero session-id */
> int ulen = len + transhdrlen;
>
> when len >= INT_MAX - 4. That will be harmless, but I guess it could
> still trigger a noisy UBSAN splat.
Good point, I wonder if that's a separate issue. Should we
follow what UDP does and subtract the transhdr from the max?
My gut feeling is that stricter checks are cleaner than just
bumping variable sizes.
diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index c6ff8bf9b55f..9dbd801ddb98 100644
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -504,14 +504,15 @@ static int l2tp_ip6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
struct ipcm6_cookie ipc6;
int addr_len = msg->msg_namelen;
int transhdrlen = 4; /* zero session-id */
- int ulen = len + transhdrlen;
+ int ulen;
int err;
/* Rough check on arithmetic overflow,
* better check is made in ip6_append_data().
*/
- if (len > INT_MAX)
+ if (len > INT_MAX - transhdrlen)
return -EMSGSIZE;
+ ulen = len + transhdrlen;
/* Mirror BSD error message compatibility */
if (msg->msg_flags & MSG_OOB)
