netdev - Re: lost connection to test machine (3)

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Date:   Thu, 28 Dec 2017 09:50:16 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Florian Westphal <fw@...len.de>
Cc:     syzbot <syzbot+4396883fa8c4f64e0175@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        David Miller <davem@...emloft.net>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev <netdev@...r.kernel.org>
Subject: Re: lost connection to test machine (3)

On Wed, Dec 27, 2017 at 10:36 PM, Florian Westphal <fw@...len.de> wrote:
> Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> On Wed, Dec 27, 2017 at 7:18 PM, syzbot
>> <syzbot+4396883fa8c4f64e0175@...kaller.appspotmail.com> wrote:
>> > Hello,
>> >
>> > syzkaller hit the following crash on
>> > beacbc68ac3e23821a681adb30b45dc55b17488d
>> > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
>> > compiler: gcc (GCC) 7.1.1 20170620
>> > .config is attached
>> > Raw console output is attached.
>> > C reproducer is attached
>> > syzkaller reproducer is attached. See https://goo.gl/kgGztJ
>> > for information about syzkaller reproducers
>> >
>> >
>> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> > Reported-by: <syzbot+4396883fa8c4f64e0175@...kaller.appspotmail.com>
>> > It will help syzbot understand when the bug is fixed. See footer for
>> > details.
>> > If you forward the report, please keep this part and the footer.
>>
>> +netfilter maintainers
>>
>> Here is cleaned reproducer:
>>
>> // autogenerated by syzkaller (http://github.com/google/syzkaller)
>> #include <sys/types.h>
>> #include <sys/socket.h>
>> #include <netinet/in.h>
>> #include <netinet/tcp.h>
>> #include <linux/if.h>
>> #include <linux/netfilter_ipv4/ip_tables.h>
>>
>> int main()
>> {
>>   int fd;
>>
>>   fd = socket(AF_INET, SOCK_STREAM, IPPROTO_IP);
>>   struct ipt_replace opt = {};
>>   opt.num_counters = 1;
>>   opt.size = -1;
>>   setsockopt(fd, SOL_IP, 0x40, &opt, 0x4);
>>   return 0;
>> }
>>
>>
>> What happens there is that here:
>>
>> struct xt_table_info *xt_alloc_table_info(unsigned int size)
>> {
>>     ...
>>     if ((SMP_ALIGN(size) >> PAGE_SHIFT) + 2 > totalram_pages)
>>         return NULL;
>>
>> size = -1 and SMP_ALIGN(size) = 0, so this still tries to allocate
>> 4GB+delta bytes.
>>
>> I don't understand why this uses SMP_ALIGN since we add 2 pages on
>> top, it seems that we could just drop SMP_ALIGN and local SMP_ALIGN
>> definition altogether.
>
> Looking at history.git this seems to be a left over from back when
> iptables allocated size * num_cpus() (and used an SMP_ALIGN based offset
> for each cpu).
>
> So yes, I think we can just toss/drop this.


Thanks.
I've mailed "netfilter: fix int overflow in xt_alloc_table_info()" to fix this.