linux-kernel - Re: [PATCH] ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff

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Message-Id: 
 <176703360579.3028177.3495525956172701388.git-patchwork-notify@kernel.org>
Date: Mon, 29 Dec 2025 18:40:05 +0000
From: patchwork-bot+netdevbpf@...nel.org
To: Will Rosenberg <whrosenb@....edu>
Cc: security@...nel.org, paul@...l-moore.com, davem@...emloft.net,
 dsahern@...nel.org, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
 horms@...nel.org, huw@...eweavers.com, netdev@...r.kernel.org,
 linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipv6: BUG() in pskb_expand_head() as part of
 calipso_skbuff_setattr()

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@...hat.com>:

On Fri, 19 Dec 2025 10:36:37 -0700 you wrote:
> There exists a kernel oops caused by a BUG_ON(nhead < 0) at
> net/core/skbuff.c:2232 in pskb_expand_head().
> This bug is triggered as part of the calipso_skbuff_setattr()
> routine when skb_cow() is passed headroom > INT_MAX
> (i.e. (int)(skb_headroom(skb) + len_delta) < 0).
> 
> The root cause of the bug is due to an implicit integer cast in
> __skb_cow(). The check (headroom > skb_headroom(skb)) is meant to ensure
> that delta = headroom - skb_headroom(skb) is never negative, otherwise
> we will trigger a BUG_ON in pskb_expand_head(). However, if
> headroom > INT_MAX and delta <= -NET_SKB_PAD, the check passes, delta
> becomes negative, and pskb_expand_head() is passed a negative value for
> nhead.
> 
> [...]

Here is the summary with links:
  - ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr()
    https://git.kernel.org/netdev/net/c/58fc7342b529

You are awesome, thank you!
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