netdev - Re: [PATCH net 3/3] ipv6: prevent possible UAF in ip6

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Message-ID: <bda78aa1-d4bd-4f9a-9b54-d7b5444177e2@kernel.org>
Date: Mon, 19 Aug 2024 09:21:27 -0600
From: David Ahern <dsahern@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>, "David S . Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com,
 Vasily Averin <vvs@...tuozzo.com>
Subject: Re: [PATCH net 3/3] ipv6: prevent possible UAF in ip6_xmit()

On 8/19/24 7:48 AM, Eric Dumazet wrote:
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 1b9ebee7308f02a626c766de1794e6b114ae8554..519690514b2d1520a311adbcfaa8c6a69b1e85d3 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -287,11 +287,15 @@ int ip6_xmit(const struct sock *sk, struct sk_buff *skb, struct flowi6 *fl6,
>  		head_room += opt->opt_nflen + opt->opt_flen;
>  
>  	if (unlikely(head_room > skb_headroom(skb))) {
> +		/* Make sure idev stays alive */
> +		rcu_read_lock();
>  		skb = skb_expand_head(skb, head_room);
>  		if (!skb) {
> +			rcu_read_unlock();
>  			IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTDISCARDS);

rcu_read_unlock after INC_STATS

>  			return -ENOBUFS;
>  		}
> +		rcu_read_unlock();
>  	}
>  
>  	if (opt) {