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Groups > linux.kernel > #1614725
| From | Denys Fedoryshchenko <nuclearcat@nuclearcat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 |
| Date | 2017-04-02 14:30 +0200 |
| Message-ID | <trMNQ-mF-5@gated-at.bofh.it> (permalink) |
| References | <trIqS-5Yh-7@gated-at.bofh.it> <trLRL-8ck-9@gated-at.bofh.it> <trMb7-8kH-19@gated-at.bofh.it> <trMkN-8nM-3@gated-at.bofh.it> <trMNP-mF-1@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 2017-04-02 15:19, Eric Dumazet wrote:
> On Sun, 2017-04-02 at 04:54 -0700, Eric Dumazet wrote:
>> On Sun, 2017-04-02 at 13:45 +0200, Florian Westphal wrote:
>> > Eric Dumazet <eric.dumazet@gmail.com> wrote:
>> > > - for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
>> > > + for (i = sizeof(struct tcphdr); i < tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
>> > > if (opt[i] == TCPOPT_MSS && opt[i+1] == TCPOLEN_MSS) {
>> > > u_int16_t oldmss;
>> >
>> > maybe I am low on caffeeine but this looks fine, for tcp header with
>> > only tcpmss this boils down to "20 <= 24 - 4" so we acccess offsets 20-23 which seems ok.
>>
>> I am definitely low on caffeine ;)
>>
>> An issue in this function is that we might add the missing MSS option,
>> without checking that TCP options are already full.
>>
>> But this should not cause a KASAN splat, only some malformed TCP
>> packet
>>
>> (tcph->doff would wrap)
>
> Something like that maybe.
>
> diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
> index
> 27241a767f17b4b27d24095a31e5e9a2d3e29ce4..1465aaf0e3a15d69d105d0a50b0429b11b6439d3
> 100644
> --- a/net/netfilter/xt_TCPMSS.c
> +++ b/net/netfilter/xt_TCPMSS.c
> @@ -151,7 +151,9 @@ tcpmss_mangle_packet(struct sk_buff *skb,
> */
> if (len > tcp_hdrlen)
> return 0;
> -
> + /* tcph->doff is 4 bits wide, do not wrap its value to 0 */
> + if (tcp_hdrlen >= 15 * 4)
> + return 0;
> /*
> * MSS Option not found ?! add it..
> */
I will add also WARN_ON_ONCE(tcp_hdrlen >= 15 * 4) before, for
curiosity, if this condition are triggered. Is it fine like that?
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KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Denys Fedoryshchenko <nuclearcat@nuclearcat.com> - 2017-04-02 09:50 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Eric Dumazet <eric.dumazet@gmail.com> - 2017-04-02 13:30 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Florian Westphal <fw@strlen.de> - 2017-04-02 13:50 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Denys Fedoryshchenko <nuclearcat@nuclearcat.com> - 2017-04-02 14:00 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Eric Dumazet <eric.dumazet@gmail.com> - 2017-04-02 14:00 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Eric Dumazet <eric.dumazet@gmail.com> - 2017-04-02 14:30 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Denys Fedoryshchenko <nuclearcat@nuclearcat.com> - 2017-04-02 14:30 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Eric Dumazet <eric.dumazet@gmail.com> - 2017-04-02 14:40 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Denys Fedoryshchenko <nuclearcat@nuclearcat.com> - 2017-04-02 19:00 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Eric Dumazet <eric.dumazet@gmail.com> - 2017-04-02 19:20 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Eric Dumazet <eric.dumazet@gmail.com> - 2017-04-02 19:30 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Denys Fedoryshchenko <nuclearcat@nuclearcat.com> - 2017-04-03 10:20 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Eric Dumazet <eric.dumazet@gmail.com> - 2017-04-03 14:10 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Denys Fedoryshchenko <nuclearcat@nuclearcat.com> - 2017-04-03 14:20 +0200
Re: KASAN, xt_TCPMSS finally found nasty use-after-free bug? 4.10.8 Eric Dumazet <eric.dumazet@gmail.com> - 2017-04-03 14:30 +0200
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