linux-kernel - Re: [PATCH ipsec-next v3] net: ipv6: fix field-spanning memcpy warning in AH output

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Message-ID: <aKHriXFxwGlTHwnq@secunet.com>
Date: Sun, 17 Aug 2025 16:47:37 +0200
From: Steffen Klassert <steffen.klassert@...unet.com>
To: Charalampos Mitrodimas <charmitro@...teo.net>
CC: Herbert Xu <herbert@...dor.apana.org.au>, "David S. Miller"
	<davem@...emloft.net>, David Ahern <dsahern@...nel.org>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<syzbot+01b0667934cdceb4451c@...kaller.appspotmail.com>
Subject: Re: [PATCH ipsec-next v3] net: ipv6: fix field-spanning memcpy
 warning in AH output

On Tue, Aug 12, 2025 at 03:51:25PM +0000, Charalampos Mitrodimas wrote:
> Fix field-spanning memcpy warnings in ah6_output() and
> ah6_output_done() where extension headers are copied to/from IPv6
> address fields, triggering fortify-string warnings about writes beyond
> the 16-byte address fields.
> 
>   memcpy: detected field-spanning write (size 40) of single field "&top_iph->saddr" at net/ipv6/ah6.c:439 (size 16)
>   WARNING: CPU: 0 PID: 8838 at net/ipv6/ah6.c:439 ah6_output+0xe7e/0x14e0 net/ipv6/ah6.c:439
> 
> The warnings are false positives as the extension headers are
> intentionally placed after the IPv6 header in memory. Fix by properly
> copying addresses and extension headers separately, and introduce
> helper functions to avoid code duplication.
> 
> Reported-by: syzbot+01b0667934cdceb4451c@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=01b0667934cdceb4451c
> Signed-off-by: Charalampos Mitrodimas <charmitro@...teo.net>

Applied, thanks a lot!