tcp: fix incorrect parameter validation in the do_tcp_getsockopt() function

[ Upstream commit 716edc9706deb3bb2ff56e2eeb83559cea8f22db ]

The 'len' variable can't be negative when assigned the result of
'min_t' because all 'min_t' parameters are cast to unsigned int,
and then the minimum one is chosen.

To fix the logic, check 'len' as read from 'optlen',
where the types of relevant variables are (signed) int.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Gavrilov Ilia <Ilia.Gavrilov@infotecs.ru>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index ab1308affa08acdde8862a339e09e5c4502066ba..68bb8d6bcc1139c81be874a791a8e02905bc76a4 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3967,11 +3967,11 @@ int do_tcp_getsockopt(struct sock *sk, int level,
        if (copy_from_sockptr(&len, optlen, sizeof(int)))
                return -EFAULT;
 
-       len = min_t(unsigned int, len, sizeof(int));
-
        if (len < 0)
                return -EINVAL;
 
+       len = min_t(unsigned int, len, sizeof(int));
+
        switch (optname) {
        case TCP_MAXSEG:
                val = tp->mss_cache;