From c2a64bb9fcd31c39feddf30748b4ee8d82e53c6a Mon Sep 17 00:00:00 2001 From: Meng Xu Date: Tue, 19 Sep 2017 13:19:13 -0400 Subject: [PATCH] net: compat: assert the size of cmsg copied in is as expected The actual length of cmsg fetched in during the second loop (i.e., kcmsg - kcmsg_base) could be different from what we get from the first loop (i.e., kcmlen). The main reason is that the two get_user() calls in the two loops (i.e., get_user(ucmlen, &ucmsg->cmsg_len) and __get_user(ucmlen, &ucmsg->cmsg_len)) could cause ucmlen to have different values even they fetch from the same userspace address, as user can race to change the memory content in &ucmsg->cmsg_len across fetches. Although in the second loop, the sanity check if ((char *)kcmsg_base + kcmlen - (char *)kcmsg < CMSG_ALIGN(tmp)) is inplace, it only ensures that the cmsg fetched in during the second loop does not exceed the length of kcmlen, but not necessarily equal to kcmlen. But indicated by the assignment kmsg->msg_controllen = kcmlen, we should enforce that. This patch adds this additional sanity check and ensures that what is recorded in kmsg->msg_controllen is the actual cmsg length. Signed-off-by: Meng Xu Signed-off-by: David S. Miller --- net/compat.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/net/compat.c b/net/compat.c index 6ded6c821d7a..22381719718c 100644 --- a/net/compat.c +++ b/net/compat.c @@ -185,6 +185,13 @@ int cmsghdr_from_user_compat_to_kern(struct msghdr *kmsg, struct sock *sk, ucmsg = cmsg_compat_nxthdr(kmsg, ucmsg, ucmlen); } + /* + * check the length of messages copied in is the same as the + * what we get from the first loop + */ + if ((char *)kcmsg - (char *)kcmsg_base != kcmlen) + goto Einval; + /* Ok, looks like we made it. Hook it up and return success. */ kmsg->msg_control = kcmsg_base; kmsg->msg_controllen = kcmlen; -- GitLab