Re: [net-next] tcp: Sanitize CMSG flags and reserved args in tcp_zerocopy_receive.

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 <redacted>
Reported-by: Dan Carpenter <redacted>

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;