[PATCH] net: compat: fix msg_controllen overflow in scm_detach_fds_compat()

[Young Xiao]

There is a missing check between kmsg->msg_controllen and cmlen,
which can possibly lead to overflow.

This bug is similar to vulnerability that was fixed in commit 6900317f5eff
("net, scm: fix PaX detected msg_controllen overflow in scm_detach_fds").

Signed-off-by: Young Xiao <92siuy...@gmail.com>
---
 net/compat.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/compat.c b/net/compat.c
index a031bd3..8e74dfb 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -301,6 +301,8 @@ void scm_detach_fds_compat(struct msghdr *kmsg, struct 
scm_cookie *scm)
                        err = put_user(cmlen, &cm->cmsg_len);
                if (!err) {
                        cmlen = CMSG_COMPAT_SPACE(i * sizeof(int));
+                       if (kmsg->msg_controllen < cmlen)
+                               cmlen = kmsg->msg_controllen;
                        kmsg->msg_control += cmlen;
                        kmsg->msg_controllen -= cmlen;
                }
-- 
2.7.4