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From:   Joerg Vehlow <lkml@jv-coder.de>
To:     linux-kernel@vger.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [RT PATCH v2] net/xfrm/xfrm_ipcomp: Protect scratch buffer with local_lock
Date:   Wed,  4 Sep 2019 07:53:14 +0200
Message-Id: <20190904055314.107024-1-lkml@jv-coder.de>
In-Reply-To: <20190820082810.ixkmi56fp7u7eyn2@linutronix.de>
References: <20190820082810.ixkmi56fp7u7eyn2@linutronix.de>
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I just happen to be analyzing an error in the kernel if ipcomp is used with rt 
patches. The reason was the meissing lock around the scratch buffer for the 
compress call. Now that I have applied Juris fix, I get another error:

[  139.717259] BUG: unable to handle kernel NULL pointer dereference at 0000000000000518
[  139.717260] PGD 0 P4D 0 
[  139.717262] Oops: 0000 [#1] PREEMPT SMP PTI
[  139.717273] CPU: 2 PID: 11987 Comm: netstress Not tainted 4.19.59-rt24-preemt-rt #1
[  139.717274] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-0-ga698c8995f-prebuilt.qemu.org 04/01/2014
[  139.717306] RIP: 0010:xfrm_trans_reinject+0x97/0xd0
[  139.717307] Code: 42 eb 45 83 6d b0 01 31 f6 48 8b 42 08 48 c7 42 08 00 00 00 00 48 8b 0a 48 c7 02 00 00 00 00 48 89 41 08 48 89 08 48 8b 42 10 <48> 8b b8 18 05 00 00 48 8b 42 40 e8 d9 e1 4b 00 48 8b 55 a0 48 39
[  139.717307] RSP: 0018:ffffc900007b37e8 EFLAGS: 00010246
[  139.717308] RAX: 0000000000000000 RBX: ffffc900007b37e8 RCX: ffff88807db206a8
[  139.717309] RDX: ffff88807db206a8 RSI: 0000000000000000 RDI: 0000000000000000
[  139.717309] RBP: ffffc900007b3848 R08: 0000000000000001 R09: ffffc900007b35c8
[  139.717309] R10: ffffea0001dcfc00 R11: 00000000000890c4 R12: ffff88807db20680
[  139.717310] R13: 00000000000f4240 R14: 0000000000000000 R15: 0000000000000000
[  139.717310] FS:  00007f4643034700(0000) GS:ffff88807db00000(0000) knlGS:0000000000000000
[  139.717311] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  139.717337] CR2: 0000000000000518 CR3: 00000000769c6000 CR4: 00000000000006e0
[  139.717350] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  139.717350] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  139.717350] Call Trace:
[  139.717387]  tasklet_action_common.isra.18+0x6d/0xd0
[  139.717388]  tasklet_action+0x1d/0x20
[  139.717389]  do_current_softirqs+0x196/0x360
[  139.717390]  __local_bh_enable+0x51/0x60
[  139.717397]  ip_finish_output2+0x18b/0x3f0
[  139.717408]  ? task_rq_lock+0x53/0xe0
[  139.717415]  ip_finish_output+0xbe/0x1b0
[  139.717416]  ip_output+0x72/0x100
[  139.717422]  ? ipcomp_output+0x5e/0x280
[  139.717424]  xfrm_output_resume+0x4b5/0x540
[  139.717436]  ? refcount_dec_and_test_checked+0x11/0x20
[  139.717443]  ? kfree_skbmem+0x33/0x80
[  139.717444]  xfrm_output+0xd7/0x110
[  139.717451]  xfrm4_output_finish+0x2b/0x30
[  139.717452]  __xfrm4_output+0x3a/0x50
[  139.717453]  xfrm4_output+0x40/0xe0
[  139.717454]  ? xfrm_dst_check+0x174/0x250
[  139.717455]  ? xfrm4_output+0x40/0xe0
[  139.717456]  ? xfrm_dst_check+0x174/0x250
[  139.717457]  ip_local_out+0x3b/0x50
[  139.717458]  __ip_queue_xmit+0x16b/0x420
[  139.717464]  ip_queue_xmit+0x10/0x20
[  139.717466]  __tcp_transmit_skb+0x566/0xad0
[  139.717467]  tcp_write_xmit+0x3a4/0x1050
[  139.717468]  __tcp_push_pending_frames+0x35/0xe0
[  139.717469]  tcp_push+0xdb/0x100
[  139.717469]  tcp_sendmsg_locked+0x491/0xd70
[  139.717470]  tcp_sendmsg+0x2c/0x50
[  139.717476]  inet_sendmsg+0x3e/0xf0
[  139.717483]  sock_sendmsg+0x3e/0x50
[  139.717484]  __sys_sendto+0x114/0x1a0
[  139.717491]  ? __rt_mutex_unlock+0xe/0x10
[  139.717492]  ? _mutex_unlock+0xe/0x10
[  139.717500]  ? ksys_write+0xc5/0xe0
[  139.717501]  __x64_sys_sendto+0x28/0x30
[  139.717503]  do_syscall_64+0x4d/0x110
[  139.717504]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Did I find some other bug here? Can you maybe point me in a direction,
because I am quite lost now where to look.


Apart from that:
Also is the bh_disable/bh_enable in ipcomp_compress even required, if
a lock is used?

Joerg