Date: Sun, 28 May 2017 00:56:54 -0700 From: Christoph Hellwig <hch@...radead.org> To: Kees Cook <keescook@...omium.org> Cc: kernel-hardening@...ts.openwall.com, Hannes Frederic Sowa <hannes@...essinduktion.org>, "Signed-off-by : David S . Miller" <davem@...emloft.net>, Laura Abbott <labbott@...hat.com>, x86@...nel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2 06/20] randstruct: Whitelist UNIXCB cast On Fri, May 26, 2017 at 01:17:10PM -0700, Kees Cook wrote: > 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 __aligned(8); > > This is a rather crazy cast, but appears to be safe in the face of > randomization, so whitelist it in the plugin. We have a lot of network protocol that use the ->cb area, which makes me wonder why this one would be so special. It seems like everyone is just using a plain cast to a pointer without doing the address taking trick that doesn't make sense for arrays anyway. Maybe we just need to fix up the af_unix code to work the same as all other protocols?
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