netdev - Re: [PATCH 4.4 stable net] net: tcp: Fix use-after-free in tcp_write

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Date:   Thu, 25 Jul 2019 08:19:52 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     maowenan <maowenan@...wei.com>,
        Eric Dumazet <eric.dumazet@...il.com>, davem@...emloft.net,
        gregkh@...uxfoundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4.4 stable net] net: tcp: Fix use-after-free in
 tcp_write_xmit



On 7/25/19 6:29 AM, maowenan wrote:
> 

>>>>> Syzkaller reproducer():
>>>>> r0 = socket$packet(0x11, 0x3, 0x300)
>>>>> r1 = socket$inet_tcp(0x2, 0x1, 0x0)
>>>>> bind$inet(r1, &(0x7f0000000300)={0x2, 0x4e21, @multicast1}, 0x10)
>>>>> connect$inet(r1, &(0x7f0000000140)={0x2, 0x1000004e21, @loopback}, 0x10)
>>>>> recvmmsg(r1, &(0x7f0000001e40)=[{{0x0, 0x0, &(0x7f0000000100)=[{&(0x7f00000005c0)=""/88, 0x58}], 0x1}}], 0x1, 0x40000000, 0x0)
>>>>> sendto$inet(r1, &(0x7f0000000000)="e2f7ad5b661c761edf", 0x9, 0x8080, 0x0, 0x0)
>>>>> r2 = fcntl$dupfd(r1, 0x0, r0)
>>>>> connect$unix(r2, &(0x7f00000001c0)=@...e={0x0, './file0\x00'}, 0x6e)
>>>>>
>>
>> It does call tcp_disconnect(), by one of the connect() call.
> 
> yes, __inet_stream_connect will call tcp_disconnect when sa_family == AF_UNSPEC, in c repro if it
> passes sa_family with AF_INET it won't call disconnect, and then sk_send_head won't be NULL when tcp_connect.
> 


Look again at the Syzkaller reproducer()

It definitely uses tcp_disconnect()

Do not be fooled by connect$unix(), this is a connect() call really, with AF_UNSPEC