ACK [CVE-2016-9793][trysty, vivid, xenial, yakkety] net: avoid signed overflows for SO_{SND|RCV}BUFFORCE

[John Donnelly]

On Mon, Dec 12, 2016 at 4:36 AM, Luis Henriques <
luis.henriques at canonical.com> wrote:

> From: Eric Dumazet <edumazet at google.com>
>
> CAP_NET_ADMIN users should not be allowed to set negative
> sk_sndbuf or sk_rcvbuf values, as it can lead to various memory
> corruptions, crashes, OOM...
>
> Note that before commit 82981930125a ("net: cleanups in
> sock_setsockopt()"), the bug was even more serious, since SO_SNDBUF
> and SO_RCVBUF were vulnerable.
>
> This needs to be backported to all known linux kernels.
>
> Again, many thanks to syzkaller team for discovering this gem.
>
> Signed-off-by: Eric Dumazet <edumazet at google.com>
> Reported-by: Andrey Konovalov <andreyknvl at google.com>
> Signed-off-by: David S. Miller <davem at davemloft.net>
> (cherry picked from commit b98b0bc8c431e3ceb4b26b0dfc8db509518fb290)
> CVE-2016-9793
> Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
> ---
>  net/core/sock.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 5dc8a067a6bb..d38777814e77 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -741,7 +741,7 @@ int sock_setsockopt(struct socket *sock, int level,
> int optname,
>                 val = min_t(u32, val, sysctl_wmem_max);
>  set_sndbuf:
>                 sk->sk_userlocks |= SOCK_SNDBUF_LOCK;
> -               sk->sk_sndbuf = max_t(u32, val * 2, SOCK_MIN_SNDBUF);
> +               sk->sk_sndbuf = max_t(int, val * 2, SOCK_MIN_SNDBUF);
>                 /* Wake up sending tasks if we upped the value. */
>                 sk->sk_write_space(sk);
>                 break;
> @@ -777,7 +777,7 @@ set_rcvbuf:
>                  * returning the value we actually used in getsockopt
>                  * is the most desirable behavior.
>                  */
> -               sk->sk_rcvbuf = max_t(u32, val * 2, SOCK_MIN_RCVBUF);
> +               sk->sk_rcvbuf = max_t(int, val * 2, SOCK_MIN_RCVBUF);
>                 break;
>
>         case SO_RCVBUFFORCE:
>
> --
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>
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