On 2/15/21 5:03 AM, Dan Carpenter wrote:
> Hi Arjun,
>
> url:
> https://github.com/0day-ci/linux/commits/Arjun-Roy/tcp-Sanitize-CMSG-flags-and-reserved-args-in-tcp_zerocopy_receive/20210212-052537
> base: https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git
> e4b62cf7559f2ef9a022de235e5a09a8d7ded520
> config: x86_64-randconfig-m001-20210209 (attached as .config)
> compiler: gcc-9 (Debian 9.3.0-15) 9.3.0
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <l...@intel.com>
> Reported-by: Dan Carpenter <dan.carpen...@oracle.com>
>
> smatch warnings:
> net/ipv4/tcp.c:4158 do_tcp_getsockopt() warn: check for integer overflow 'len'
>
> vim +/len +4158 net/ipv4/tcp.c
>
> 3fdadf7d27e3fb Dmitry Mishin 2006-03-20 3896 static int
> do_tcp_getsockopt(struct sock *sk, int level,
> 3fdadf7d27e3fb Dmitry Mishin 2006-03-20 3897 int
> optname, char __user *optval, int __user *optlen)
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 3898 {
> 295f7324ff8d9e Arnaldo Carvalho de Melo 2005-08-09 3899 struct
> inet_connection_sock *icsk = inet_csk(sk);
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 3900 struct tcp_sock
> *tp = tcp_sk(sk);
> 6fa251663069e0 Nikolay Borisov 2016-02-03 3901 struct net *net
> = sock_net(sk);
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 3902 int val, len;
>
> "len" is int.
>
> [ snip ]
> 05255b823a6173 Eric Dumazet 2018-04-27 4146 #ifdef CONFIG_MMU
> 05255b823a6173 Eric Dumazet 2018-04-27 4147 case
> TCP_ZEROCOPY_RECEIVE: {
> 7eeba1706eba6d Arjun Roy 2021-01-20 4148 struct
> scm_timestamping_internal tss;
> e0fecb289ad3fd Arjun Roy 2020-12-10 4149 struct
> tcp_zerocopy_receive zc = {};
> 05255b823a6173 Eric Dumazet 2018-04-27 4150 int err;
> 05255b823a6173 Eric Dumazet 2018-04-27 4151
> 05255b823a6173 Eric Dumazet 2018-04-27 4152 if
> (get_user(len, optlen))
> 05255b823a6173 Eric Dumazet 2018-04-27 4153
> return -EFAULT;
> c8856c05145490 Arjun Roy 2020-02-14 4154 if (len
> < offsetofend(struct tcp_zerocopy_receive, length))
> 05255b823a6173 Eric Dumazet 2018-04-27 4155
> return -EINVAL;
>
>
> The problem is that negative values of "len" are type promoted to high
> positive values. So the fix is to write this as:
>
> if (len < 0 || len < offsetofend(struct tcp_zerocopy_receive, length))
> return -EINVAL;
>
> 110912bdf28392 Arjun Roy 2021-02-11 4156 if
> (unlikely(len > sizeof(zc))) {
> 110912bdf28392 Arjun Roy 2021-02-11 4157
> err = check_zeroed_user(optval + sizeof(zc),
> 110912bdf28392 Arjun Roy 2021-02-11 @4158
> len - sizeof(zc));
>
> ^^^^^^^^^^^^^^^^
> Potentially "len - a negative value".
>
>
get_user(len, optlen) is called multiple times in that function. len < 0
was checked after the first one at the top.
Also, maybe I am missing something here, but offsetofend can not return
a negative value, so this checks catches len < 0 as well:
if (len < offsetofend(struct tcp_zerocopy_receive, length))
return -EINVAL;
