linux-hardening - Re: [PATCH v3] sock: Use unsafe_memcpy() for sock

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Date: Tue, 5 Mar 2024 13:23:26 +0000
From: Simon Horman <horms@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Jakub Kicinski <kuba@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, David Ahern <dsahern@...nel.org>,
	Kuniyuki Iwashima <kuniyu@...zon.com>,
	Abel Wu <wuyun.abel@...edance.com>,
	Breno Leitao <leitao@...ian.org>,
	Alexander Mikhalitsyn <alexander@...alicyn.com>,
	David Howells <dhowells@...hat.com>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3] sock: Use unsafe_memcpy() for sock_copy()

On Mon, Mar 04, 2024 at 01:29:31PM -0800, Kees Cook wrote:
> While testing for places where zero-sized destinations were still showing
> up in the kernel, sock_copy() and inet_reqsk_clone() were found, which
> are using very specific memcpy() offsets for both avoiding a portion of
> struct sock, and copying beyond the end of it (since struct sock is really
> just a common header before the protocol-specific allocation). Instead
> of trying to unravel this historical lack of container_of(), just switch
> to unsafe_memcpy(), since that's effectively what was happening already
> (memcpy() wasn't checking 0-sized destinations while the code base was
> being converted away from fake flexible arrays).
> 
> Avoid the following false positive warning with future changes to
> CONFIG_FORTIFY_SOURCE:
> 
>   memcpy: detected field-spanning write (size 3068) of destination "&nsk->__sk_common.skc_dontcopy_end" at net/core/sock.c:2057 (size 0)
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: netdev@...r.kernel.org
>  v3: fix inet_reqsk_clone() comment
>  v2: https://lore.kernel.org/lkml/20240216232220.it.450-kees@kernel.org
>  v1: https://lore.kernel.org/lkml/20240216204423.work.066-kees@kernel.org

Reviewed-by: Simon Horman <horms@...nel.org>