netdev - Re: [PATCH] af_unix: Add sockaddr length checks before accessing sa

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Message-Id: <20170608.160425.3981801836671654.davem@davemloft.net>
Date:   Thu, 08 Jun 2017 16:04:25 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     mjurczyk@...gle.com
Cc:     xiyou.wangcong@...il.com, hannes@...essinduktion.org,
        viro@...iv.linux.org.uk, keescook@...omium.org,
        mszeredi@...hat.com, iboukris@...il.com, avagin@...nvz.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] af_unix: Add sockaddr length checks before accessing
 sa_family in bind and connect handlers

From: Mateusz Jurczyk <mjurczyk@...gle.com>
Date: Thu,  8 Jun 2017 11:13:36 +0200

> Verify that the caller-provided sockaddr structure is large enough to
> contain the sa_family field, before accessing it in bind() and connect()
> handlers of the AF_UNIX socket. Since neither syscall enforces a minimum
> size of the corresponding memory region, very short sockaddrs (zero or
> one byte long) result in operating on uninitialized memory while
> referencing .sa_family.
> 
> Signed-off-by: Mateusz Jurczyk <mjurczyk@...gle.com>

The sockaddr comes from a structure on the caller's kernel stack, even
if the user gives a smaller length, it is legal to access that memory.