randstruct: Whitelist UNIXCB cast

This is another false positive in bad cast detection:

net/unix/af_unix.c: In function ‘unix_skb_scm_eq’:
net/unix/af_unix.c:1621:31: note: found mismatched rhs struct pointer types: ‘struct unix_skb_parms’ and ‘char’

  const struct unix_skb_parms *u = &UNIXCB(skb);
                               ^

UNIXCB is:

	#define UNIXCB(skb)     (*(struct unix_skb_parms *)&((skb)->cb))

And ->cb is:

	char                    cb[48] __aligned(8);

This is a rather crazy cast, but appears to be safe in the face of
randomization, so whitelist it in the plugin.

Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/scripts/gcc-plugins/randomize_layout_plugin.c b/scripts/gcc-plugins/randomize_layout_plugin.c
index dc0df3765a8fef37f6420570eaf467a045ac210d..2e710bf29699924ab40fa9566b48292f119a365b 100644 (file)
--- a/scripts/gcc-plugins/randomize_layout_plugin.c
+++ b/scripts/gcc-plugins/randomize_layout_plugin.c
@@ -46,6 +46,8 @@ struct whitelist_entry {
 };
 
 static const struct whitelist_entry whitelist[] = {
+       /* unix_skb_parms via UNIXCB() buffer */
+       { "net/unix/af_unix.c", "unix_skb_parms", "char" },
        /* walk struct security_hook_heads as an array of struct list_head */
        { "security/security.c", "list_head", "security_hook_heads" },
        { }