Re: [PATCH stable 4.9] tcp: reset sk_send_head in tcp_write_queue_purge

From: Sasha Levin <sashal@kernel.org>
To: maowenan <maowenan@huawei.com>
Cc: gregkh@linuxfoundation.org, stable@vger.kernel.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH stable 4.9] tcp: reset sk_send_head in tcp_write_queue_purge
Date: Tue, 30 Jul 2019 16:17:52 -0400	[thread overview]
Message-ID: <20190730201752.GE29162@sasha-vm> (raw)
In-Reply-To: <29c1ee9c-4a5d-4f61-f526-85980185f0bd@huawei.com>

On Tue, Jul 30, 2019 at 09:31:19AM +0800, maowenan wrote:
>
>
>On 2019/7/29 23:32, Sasha Levin wrote:
>> On Mon, Jul 29, 2019 at 09:21:08PM +0800, Mao Wenan wrote:
>>> From: Soheil Hassas Yeganeh <soheil@google.com>
>>>
>>> tcp_write_queue_purge clears all the SKBs in the write queue
>>> but does not reset the sk_send_head. As a result, we can have
>>> a NULL pointer dereference anywhere that we use tcp_send_head
>>> instead of the tcp_write_queue_tail.
>>>
>>> For example, after a27fd7a8ed38 (tcp: purge write queue upon RST),
>>> we can purge the write queue on RST. Prior to
>>> 75c119afe14f (tcp: implement rb-tree based retransmit queue),
>>> tcp_push will only check tcp_send_head and then accesses
>>> tcp_write_queue_tail to send the actual SKB. As a result, it will
>>> dereference a NULL pointer.
>>>
>>> This has been reported twice for 4.14 where we don't have
>>> 75c119afe14f:
>>>
>>> By Timofey Titovets:
>>>
>>> [  422.081094] BUG: unable to handle kernel NULL pointer dereference
>>> at 0000000000000038
>>> [  422.081254] IP: tcp_push+0x42/0x110
>>> [  422.081314] PGD 0 P4D 0
>>> [  422.081364] Oops: 0002 [#1] SMP PTI
>>>
>>> By Yongjian Xu:
>>>
>>> BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
>>> IP: tcp_push+0x48/0x120
>>> PGD 80000007ff77b067 P4D 80000007ff77b067 PUD 7fd989067 PMD 0
>>> Oops: 0002 [#18] SMP PTI
>>> Modules linked in: tcp_diag inet_diag tcp_bbr sch_fq iTCO_wdt
>>> iTCO_vendor_support pcspkr ixgbe mdio i2c_i801 lpc_ich joydev input_leds shpchp
>>> e1000e igb dca ptp pps_core hwmon mei_me mei ipmi_si ipmi_msghandler sg ses
>>> scsi_transport_sas enclosure ext4 jbd2 mbcache sd_mod ahci libahci megaraid_sas
>>> wmi ast ttm dm_mirror dm_region_hash dm_log dm_mod dax
>>> CPU: 6 PID: 14156 Comm: [ET_NET 6] Tainted: G D 4.14.26-1.el6.x86_64 #1
>>> Hardware name: LENOVO ThinkServer RD440 /ThinkServer RD440, BIOS A0TS80A
>>> 09/22/2014
>>> task: ffff8807d78d8140 task.stack: ffffc9000e944000
>>> RIP: 0010:tcp_push+0x48/0x120
>>> RSP: 0018:ffffc9000e947a88 EFLAGS: 00010246
>>> RAX: 00000000000005b4 RBX: ffff880f7cce9c00 RCX: 0000000000000000
>>> RDX: 0000000000000000 RSI: 0000000000000040 RDI: ffff8807d00f5000
>>> RBP: ffffc9000e947aa8 R08: 0000000000001c84 R09: 0000000000000000
>>> R10: ffff8807d00f5158 R11: 0000000000000000 R12: ffff8807d00f5000
>>> R13: 0000000000000020 R14: 00000000000256d4 R15: 0000000000000000
>>> FS: 00007f5916de9700(0000) GS:ffff88107fd00000(0000) knlGS:0000000000000000
>>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: 0000000000000038 CR3: 00000007f8226004 CR4: 00000000001606e0
>>> Call Trace:
>>> tcp_sendmsg_locked+0x33d/0xe50
>>> tcp_sendmsg+0x37/0x60
>>> inet_sendmsg+0x39/0xc0
>>> sock_sendmsg+0x49/0x60
>>> sock_write_iter+0xb6/0x100
>>> do_iter_readv_writev+0xec/0x130
>>> ? rw_verify_area+0x49/0xb0
>>> do_iter_write+0x97/0xd0
>>> vfs_writev+0x7e/0xe0
>>> ? __wake_up_common_lock+0x80/0xa0
>>> ? __fget_light+0x2c/0x70
>>> ? __do_page_fault+0x1e7/0x530
>>> do_writev+0x60/0xf0
>>> ? inet_shutdown+0xac/0x110
>>> SyS_writev+0x10/0x20
>>> do_syscall_64+0x6f/0x140
>>> ? prepare_exit_to_usermode+0x8b/0xa0
>>> entry_SYSCALL_64_after_hwframe+0x3d/0xa2
>>> RIP: 0033:0x3135ce0c57
>>> RSP: 002b:00007f5916de4b00 EFLAGS: 00000293 ORIG_RAX: 0000000000000014
>>> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000003135ce0c57
>>> RDX: 0000000000000002 RSI: 00007f5916de4b90 RDI: 000000000000606f
>>> RBP: 0000000000000000 R08: 0000000000000000 R09: 00007f5916de8c38
>>> R10: 0000000000000000 R11: 0000000000000293 R12: 00000000000464cc
>>> R13: 00007f5916de8c30 R14: 00007f58d8bef080 R15: 0000000000000002
>>> Code: 48 8b 97 60 01 00 00 4c 8d 97 58 01 00 00 41 b9 00 00 00 00 41 89 f3 4c 39
>>> d2 49 0f 44 d1 41 81 e3 00 80 00 00 0f 85 b0 00 00 00 <80> 4a 38 08 44 8b 8f 74
>>> 06 00 00 44 89 8f 7c 06 00 00 83 e6 01
>>> RIP: tcp_push+0x48/0x120 RSP: ffffc9000e947a88
>>> CR2: 0000000000000038
>>> ---[ end trace 8d545c2e93515549 ]---
>>>
>>> There is other scenario which found in stable 4.4:
>>> Allocated:
>>> [<ffffffff82f380a6>] __alloc_skb+0xe6/0x600 net/core/skbuff.c:218
>>> [<ffffffff832466c3>] alloc_skb_fclone include/linux/skbuff.h:856 [inline]
>>> [<ffffffff832466c3>] sk_stream_alloc_skb+0xa3/0x5d0 net/ipv4/tcp.c:833
>>> [<ffffffff83249164>] tcp_sendmsg+0xd34/0x2b00 net/ipv4/tcp.c:1178
>>> [<ffffffff83300ef3>] inet_sendmsg+0x203/0x4d0 net/ipv4/af_inet.c:755
>>> Freed:
>>> [<ffffffff82f372fd>] __kfree_skb+0x1d/0x20 net/core/skbuff.c:676
>>> [<ffffffff83288834>] sk_wmem_free_skb include/net/sock.h:1447 [inline]
>>> [<ffffffff83288834>] tcp_write_queue_purge include/net/tcp.h:1460 [inline]
>>> [<ffffffff83288834>] tcp_connect_init net/ipv4/tcp_output.c:3122 [inline]
>>> [<ffffffff83288834>] tcp_connect+0xb24/0x30c0 net/ipv4/tcp_output.c:3261
>>> [<ffffffff8329b991>] tcp_v4_connect+0xf31/0x1890 net/ipv4/tcp_ipv4.c:246
>>>
>>> BUG: KASAN: use-after-free in tcp_skb_pcount include/net/tcp.h:796 [inline]
>>> BUG: KASAN: use-after-free in tcp_init_tso_segs net/ipv4/tcp_output.c:1619 [inline]
>>> BUG: KASAN: use-after-free in tcp_write_xmit+0x3fc2/0x4cb0 net/ipv4/tcp_output.c:2056
>>> [<ffffffff81515cd5>] kasan_report.cold.7+0x175/0x2f7 mm/kasan/report.c:408
>>> [<ffffffff814f9784>] __asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:427
>>> [<ffffffff83286582>] tcp_skb_pcount include/net/tcp.h:796 [inline]
>>> [<ffffffff83286582>] tcp_init_tso_segs net/ipv4/tcp_output.c:1619 [inline]
>>> [<ffffffff83286582>] tcp_write_xmit+0x3fc2/0x4cb0 net/ipv4/tcp_output.c:2056
>>> [<ffffffff83287a40>] __tcp_push_pending_frames+0xa0/0x290 net/ipv4/tcp_output.c:2307
>>>
>>> stable 4.4 and stable 4.9 don't have the commit abb4a8b870b5 ("tcp: purge write queue upon RST")
>>> which is referred in dbbf2d1e4077,
>>> in tcp_connect_init, it calls tcp_write_queue_purge, and does not reset sk_send_head, then UAF.
>>>
>>> stable 4.14 have the commit abb4a8b870b5 ("tcp: purge write queue upon RST"),
>>> in tcp_reset, it calls tcp_write_queue_purge(sk), and does not reset sk_send_head, then UAF.
>>>
>>> So this patch can be used to fix stable 4.4 and 4.9.
>>>
>>> Fixes: a27fd7a8ed38 (tcp: purge write queue upon RST)
>>> Reported-by: Timofey Titovets <nefelim4ag@gmail.com>
>>> Reported-by: Yongjian Xu <yongjianchn@gmail.com>
>>> Signed-off-by: Eric Dumazet <edumazet@google.com>
>>> Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
>>> Tested-by: Yongjian Xu <yongjianchn@gmail.com>
>>>
>>> Signed-off-by: David S. Miller <davem@davemloft.net>
>>> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>> Signed-off-by: Mao Wenan <maowenan@huawei.com>
>>
>> So the "Fixes:" commit in the commit message is wrong? What's the actual
>> commit that this fixes?
>
>Upstream commit is 7f582b248d0a ("tcp: purge write queue in tcp_connect_init()")
>linux-4.4.y
>Fixes: 5bbe138a250e ("tcp: purge write queue in tcp_connect_init()")
>linux-4.9.y
>Fixes: 74a4c09d4b05 ("tcp: purge write queue in tcp_connect_init()")
>linux-4.14.y
>Fixes: a27fd7a8ed38 ("tcp: purge write queue upon RST")

Okay, I've queued this for 4.9 and 4.4, thank you.

--
Thanks,
Sasha