linux-kernel - Re: [PATCH v2] NFS: Avoid memcpy() run-time warning for struct sockaddr overflows

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Message-ID: <202210261631.DE7E4761E@keescook>
Date:   Wed, 26 Oct 2022 16:32:40 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Trond Myklebust <trond.myklebust@...merspace.com>
Cc:     kernel test robot <yujie.liu@...el.com>,
        Anna Schumaker <anna@...nel.org>, linux-nfs@...r.kernel.org,
        Dave Jones <davej@...emonkey.org.uk>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] NFS: Avoid memcpy() run-time warning for struct
 sockaddr overflows

On Sun, Oct 16, 2022 at 09:36:50PM -0700, Kees Cook wrote:
> The 'nfs_server' and 'mount_server' structures include a union of
> 'struct sockaddr' (with the older 16 bytes max address size) and
> 'struct sockaddr_storage' which is large enough to hold all the
> supported sa_family types (128 bytes max size). The runtime memcpy()
> buffer overflow checker is seeing attempts to write beyond the 16
> bytes as an overflow, but the actual expected size is that of 'struct
> sockaddr_storage'. Plumb the use of 'struct sockaddr_storage' more
> completely through-out NFS, which results in adjusting the memcpy()
> buffers to the correct union members. Avoids this false positive run-time
> warning under CONFIG_FORTIFY_SOURCE:
> 
>   memcpy: detected field-spanning write (size 28) of single field "&ctx->nfs_server.address" at fs/nfs/namespace.c:178 (size 16)
> 
> Reported-by: kernel test robot <yujie.liu@...el.com>
> Link: https://lore.kernel.org/all/202210110948.26b43120-yujie.liu@intel.com
> Cc: Trond Myklebust <trond.myklebust@...merspace.com>
> Cc: Anna Schumaker <anna@...nel.org>

Friendly ping -- this needs to land in v6.1 to avoid these warnings.
Should I carry this in the hardening tree instead?

Thanks!

-Kees

-- 
Kees Cook