Date:   Wed, 21 Sep 2022 10:50:19 +0800
From:   zhenwei pi <pizhenwei@...edance.com>
To:     Sagi Grimberg <sagi@...mberg.me>, hch@....de
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: Re: [RESEND for nvme-6.1] nvmet-tcp: Fix NULL pointer dereference
 during release

On 9/20/22 23:34, Sagi Grimberg wrote:
> 
> 
> On 9/20/22 16:16, zhenwei pi wrote:
>> nvmet-tcp frees CMD buffers in nvmet_tcp_uninit_data_in_cmds(),
>> and waits the inflight IO requests in nvmet_sq_destroy(). During wait
>> the inflight IO requests, the callback nvmet_tcp_queue_response()
>> is called from backend after IO complete, this leads a typical
>> Use-After-Free issue like this:
>>
>>   BUG: kernel NULL pointer dereference, address: 0000000000000008
>>   #PF: supervisor read access in kernel mode
>>   #PF: error_code(0x0000) - not-present page
>>   PGD 107f80067 P4D 107f80067 PUD 10789e067 PMD 0
>>   Oops: 0000 [#1] PREEMPT SMP NOPTI
>>   CPU: 1 PID: 123 Comm: kworker/1:1H Kdump: loaded Tainted: 
>> G            E      6.0.0-rc2.bm.1-amd64 #15
>>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
>> rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
>>   Workqueue: nvmet_tcp_wq nvmet_tcp_io_work [nvmet_tcp]
>>   RIP: 0010:shash_ahash_digest+0x2b/0x110
>>   Code: 1f 44 00 00 41 57 41 56 41 55 41 54 55 48 89 fd 53 48 89 f3 48 
>> 83 ec 08 44 8b 67 30 45 85 e4 74 1c 48 8b 57 38 b8 00 10 00 00 <44> 8b 
>> 7a 08 44 29 f8 39 42 0c 0f 46 42 0c 41 39 c4 76 43 48 8b 03
>>   RSP: 0018:ffffc9000051bdd8 EFLAGS: 00010206
>>   RAX: 0000000000001000 RBX: ffff888100ab5470 RCX: 0000000000000000
>>   RDX: 0000000000000000 RSI: ffff888100ab5470 RDI: ffff888100ab5420
>>   RBP: ffff888100ab5420 R08: ffff8881024d08c8 R09: ffff888103e1b4b8
>>   R10: 8080808080808080 R11: 0000000000000000 R12: 0000000000001000
>>   R13: 0000000000000000 R14: ffff88813412bd4c R15: ffff8881024d0800
>>   FS:  0000000000000000(0000) GS:ffff88883fa40000(0000) 
>> knlGS:0000000000000000
>>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>   CR2: 0000000000000008 CR3: 0000000104b48000 CR4: 0000000000350ee0
>>   Call Trace:
>>    <TASK>
>>    nvmet_tcp_io_work+0xa52/0xb52 [nvmet_tcp]
>>    ? __switch_to+0x106/0x420
>>    process_one_work+0x1ae/0x380
>>    ? process_one_work+0x380/0x380
>>    worker_thread+0x30/0x360
>>    ? process_one_work+0x380/0x380
>>    kthread+0xe6/0x110
>>    ? kthread_complete_and_exit+0x20/0x20
>>    ret_from_fork+0x1f/0x30
>>
>> Suggested by Sagi, separate nvmet_tcp_uninit_data_in_cmds() into two
>> steps:
>>    uninit data in cmds                  <- new step 1
>>    nvmet_sq_destroy();
>>    cancel_work_sync(&queue->io_work);
>>    free CMD buffers                     <- new step 2
>>
>> Signed-off-by: zhenwei pi <pizhenwei@...edance.com>
>> ---
>>   drivers/nvme/target/tcp.c | 19 ++++++++++++++++---
>>   1 file changed, 16 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/nvme/target/tcp.c b/drivers/nvme/target/tcp.c
>> index c07de4f4f719..70baeab6af30 100644
>> --- a/drivers/nvme/target/tcp.c
>> +++ b/drivers/nvme/target/tcp.c
>> @@ -1406,14 +1406,26 @@ static void 
>> nvmet_tcp_uninit_data_in_cmds(struct nvmet_tcp_queue *queue)
>>       for (i = 0; i < queue->nr_cmds; i++, cmd++) {
>>           if (nvmet_tcp_need_data_in(cmd))
>>               nvmet_req_uninit(&cmd->req);
>> -
>> -        nvmet_tcp_free_cmd_buffers(cmd);
>>       }
>>       if (!queue->nr_cmds && nvmet_tcp_need_data_in(&queue->connect)) {
>>           /* failed in connect */
>> -        nvmet_tcp_finish_cmd(&queue->connect);
> 
> I think that nvmet_tcp_finish_cmd is now redundant and can be removed
> if we fold it to its single remaining call-site.
> 

Hi, Sagi

What about letting this patch fix the kernel panic only, and I'll send a 
followup patch to remove nvmet_tcp_finish_cmd after this patch applies?

> Other than that,
> Reviewed-by: Sagi Grimberg <sagi@...mberg.me>

-- 
zhenwei pi

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