netdev - Re: [PATCH net-next v4] ipv6: Fix signed integer overflow in __ip6_append

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Message-ID: <4c9e3cf5122f4c2f8a2473c493891362e0a13b4a.camel@redhat.com>
Date:   Thu, 02 Jun 2022 12:38:10 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Wang Yufen <wangyufen@...wei.com>, davem@...emloft.net,
        yoshfuji@...ux-ipv6.org, dsahern@...nel.org, edumazet@...gle.com,
        kuba@...nel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH net-next v4] ipv6: Fix signed integer overflow in
 __ip6_append_data

On Wed, 2022-06-01 at 16:48 +0800, Wang Yufen wrote:
> Resurrect ubsan overflow checks and ubsan report this warning,
> fix it by change the variable [length] type to size_t.
> 
> UBSAN: signed-integer-overflow in net/ipv6/ip6_output.c:1489:19
> 2147479552 + 8567 cannot be represented in type 'int'
> CPU: 0 PID: 253 Comm: err Not tainted 5.16.0+ #1
> Hardware name: linux,dummy-virt (DT)
> Call trace:
>   dump_backtrace+0x214/0x230
>   show_stack+0x30/0x78
>   dump_stack_lvl+0xf8/0x118
>   dump_stack+0x18/0x30
>   ubsan_epilogue+0x18/0x60
>   handle_overflow+0xd0/0xf0
>   __ubsan_handle_add_overflow+0x34/0x44
>   __ip6_append_data.isra.48+0x1598/0x1688
>   ip6_append_data+0x128/0x260
>   udpv6_sendmsg+0x680/0xdd0
>   inet6_sendmsg+0x54/0x90
>   sock_sendmsg+0x70/0x88
>   ____sys_sendmsg+0xe8/0x368
>   ___sys_sendmsg+0x98/0xe0
>   __sys_sendmmsg+0xf4/0x3b8
>   __arm64_sys_sendmmsg+0x34/0x48
>   invoke_syscall+0x64/0x160
>   el0_svc_common.constprop.4+0x124/0x300
>   do_el0_svc+0x44/0xc8
>   el0_svc+0x3c/0x1e8
>   el0t_64_sync_handler+0x88/0xb0
>   el0t_64_sync+0x16c/0x170
> 
> Changes since v1:
> -Change the variable [length] type to unsigned, as Eric Dumazet suggested.
> Changes since v2:
> -Don't change exthdrlen type in ip6_make_skb, as Paolo Abeni suggested.
> Changes since v3:
> -Don't change ulen type in udpv6_sendmsg and l2tp_ip6_sendmsg, as
> Jakub Kicinski suggested.

I'm sorry for the multiple incremental feedback on this patch. It's
somewhat tricky.

AFAICS Jakub mentioned only udpv6_sendmsg(). In l2tp_ip6_sendmsg() we
can have an overflow:

        int transhdrlen = 4; /* zero session-id */
        int ulen = len + transhdrlen;

when len >= INT_MAX - 4. That will be harmless, but I guess it could
still trigger a noisy UBSAN splat. 

Paolo