ipv6: Fix signed integer overflow in l2tp_ip6_sendmsg

When len >= INT_MAX - transhdrlen, ulen = len + transhdrlen will be
overflow. To fix, we can follow what udpv6 does and subtract the
transhdrlen from the max.

Signed-off-by: Wang Yufen <wangyufen@huawei.com>
Link: https://lore.kernel.org/r/20220607120028.845916-2-wangyufen@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index c6ff8bf9b55f916e80380bb2e4ea81b11e544a32..9dbd801ddb98c7f0878ffa69fda8113490344fda 100644 (file)
--- 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)