net: Assert at build time the assumptions we make about the CMSG header.

It must always be the case that CMSG_ALIGN(sizeof(hdr)) == sizeof(hdr).

Otherwise there are missing adjustments in the various calculations
that parse and build these things.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/compat.c b/net/compat.c
index 4e27dd1cd3a6..ba3ac722714d 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -130,6 +130,9 @@ int cmsghdr_from_user_compat_to_kern(struct msghdr *kmsg, struct sock *sk,
         __kernel_size_t kcmlen, tmp;
         int err = -EFAULT;
 
+        BUILD_BUG_ON(sizeof(struct compat_cmsghdr) !=
+                     CMSG_COMPAT_ALIGN(sizeof(struct compat_cmsghdr)));
+
         kcmlen = 0;
         kcmsg_base = kcmsg = (struct cmsghdr *)stackbuf;
         ucmsg = CMSG_COMPAT_FIRSTHDR(kmsg);