[PATCH net] net: socket: add check for negative optlen in compat setsockopt

[Jann Horn]

__sys_setsockopt() already checks for `optlen < 0`. Add an equivalent check
to the compat path for robustness. This has to be `> INT_MAX` instead of
`< 0` because the signedness of `optlen` is different here.

Signed-off-by: Jann Horn <ja...@google.com>
---
 net/compat.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/compat.c b/net/compat.c
index 959d1c51826d..3d348198004f 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -388,8 +388,12 @@ static int __compat_sys_setsockopt(int fd, int level, int 
optname,
                                   char __user *optval, unsigned int optlen)
 {
        int err;
-       struct socket *sock = sockfd_lookup(fd, &err);
+       struct socket *sock;
+
+       if (optlen > INT_MAX)
+               return -EINVAL;
 
+       sock = sockfd_lookup(fd, &err);
        if (sock) {
                err = security_socket_setsockopt(sock, level, optname);
                if (err) {
-- 
2.21.0.rc0.258.g878e2cd30e-goog