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

From: Sasha Levin <[email-masked]>
Date: Mon, 29 Jul 2019 11:32:18 -0400

On Mon, Jul 29, 2019 at 09:21:08PM +0800, Mao Wenan wrote:
>From: Soheil Hassas Yeganeh <[email-masked]>
>
>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 <[email-masked]>
>Reported-by: Yongjian Xu <[email-masked]>
>Signed-off-by: Eric Dumazet <[email-masked]>
>Signed-off-by: Soheil Hassas Yeganeh <[email-masked]>
>Tested-by: Yongjian Xu <[email-masked]>
>
>Signed-off-by: David S. Miller <[email-masked]>
>Signed-off-by: Greg Kroah-Hartman <[email-masked]>
>Signed-off-by: Mao Wenan <[email-masked]>

So the "Fixes:" commit in the commit message is wrong? What's the actual
commit that this fixes?

--
Thanks,
Sasha