path: root/net/compat.c
diff options
authorMeng Xu <mengxu.gatech@gmail.com>2017-09-19 13:19:13 -0400
committerDavid S. Miller <davem@davemloft.net>2017-09-20 15:36:18 -0700
commitc2a64bb9fcd31c39feddf30748b4ee8d82e53c6a (patch)
treebae30a193cb370d73f658d404cbfef45882f0a77 /net/compat.c
parentec9dd352d591f0c90402ec67a317c1ed4fb2e638 (diff)
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 <mengxu.gatech@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/compat.c')
1 files changed, 7 insertions, 0 deletions
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;