netdev - Re: [PATCH linux-5.9 1/1] net: netfilter: fix KASAN: slab-out-of-bounds Read in nft_flow_rule

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Date:   Tue, 20 Oct 2020 13:50:47 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     saeed.mirzamohammadi@...cle.com
Cc:     linux-kernel@...r.kernel.org, kadlec@...filter.org, fw@...len.de,
        davem@...emloft.net, kuba@...nel.org,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH linux-5.9 1/1] net: netfilter: fix KASAN:
 slab-out-of-bounds Read in nft_flow_rule_create

On Mon, Oct 19, 2020 at 10:25:32AM -0700, saeed.mirzamohammadi@...cle.com wrote:
> From: Saeed Mirzamohammadi <saeed.mirzamohammadi@...cle.com>
> 
> This patch fixes the issue due to:
> 
> BUG: KASAN: slab-out-of-bounds in nft_flow_rule_create+0x622/0x6a2
> net/netfilter/nf_tables_offload.c:40
> Read of size 8 at addr ffff888103910b58 by task syz-executor227/16244
> 
> The error happens when expr->ops is accessed early on before performing the boundary check and after nft_expr_next() moves the expr to go out-of-bounds.
> 
> This patch checks the boundary condition before expr->ops that fixes the slab-out-of-bounds Read issue.

Thanks. I made a slight variant of your patch.

I'm attaching it, it is also fixing the problem but it introduced
nft_expr_more() and use it everywhere.

Let me know if this looks fine to you.

View attachment "0001-netfilter-fix-KASAN-slab-out-of-bounds-Read-in-nft_f.patch" of type "text/x-diff" (3702 bytes)