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

[Pablo Neira Ayuso]

 On Mon, Oct 19, 2020 at 10:25:32AM -0700, saeed.mirzamohammadi@xxxxxxxxxx wrote:
> From: Saeed Mirzamohammadi <saeed.mirzamohammadi@xxxxxxxxxx>
> 
> 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.