Re: [PATCH] RDMA/srp: Set scmnd->result only when scmnd is not NULL

[Li Zhijian <lizhijian@fujitsu.com>]

On 31/08/2022 09:47, yangx.jy@fujitsu.com wrote:
> This change fixes the following kernel NULL pointer dereference
> which is reproduced by blktests srp/007 occasionally.
>
> BUG: kernel NULL pointer dereference, address: 0000000000000170
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0002) - not-present page
> PGD 0 P4D 0
> Oops: 0002 [#1] PREEMPT SMP NOPTI
> CPU: 0 PID: 9 Comm: kworker/0:1H Kdump: loaded Not tainted 6.0.0-rc1+ #37
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.15.0-29-g6a62e0cb0dfe-prebuilt.qemu.org 04/01/2014
> Workqueue:  0x0 (kblockd)
> RIP: 0010:srp_recv_done+0x176/0x500 [ib_srp]
> Code: 00 4d 85 ff 0f 84 52 02 00 00 48 c7 82 80 02 00 00 00 00 00 00 4c 89 df 4c 89 14 24 e8 53 d3 4a f6 4c 8b 14 24 41 0f b6 42 13 <41> 89 87 70 01 00 00 41 0f b6 52 12 f6 c2 02 74 44 41 8b 42 1c b9
> RSP: 0018:ffffaef7c0003e28 EFLAGS: 00000282
> RAX: 0000000000000000 RBX: ffff9bc9486dea60 RCX: 0000000000000000
> RDX: 0000000000000102 RSI: ffffffffb76bbd0e RDI: 00000000ffffffff
> RBP: ffff9bc980099a00 R08: 0000000000000001 R09: 0000000000000001
> R10: ffff9bca53ef0000 R11: ffff9bc980099a10 R12: ffff9bc956e14000
> R13: ffff9bc9836b9cb0 R14: ffff9bc9557b4480 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffff9bc97ec00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000170 CR3: 0000000007e04000 CR4: 00000000000006f0
> Call Trace:
>   <IRQ>
>   __ib_process_cq+0xb7/0x280 [ib_core]
>   ib_poll_handler+0x2b/0x130 [ib_core]
>   irq_poll_softirq+0x93/0x150
>   __do_softirq+0xee/0x4b8
>   irq_exit_rcu+0xf7/0x130
>   sysvec_apic_timer_interrupt+0x8e/0xc0
>   </IRQ>
>
> Fixes: aef9ec39c47f ("IB: Add SCSI RDMA Protocol (SRP) initiator")
> Signed-off-by: Xiao Yang <yangx.jy@fujitsu.com>
> ---
>   drivers/infiniband/ulp/srp/ib_srp.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
> index 7720ea270ed8..528cdd0daba4 100644
> --- a/drivers/infiniband/ulp/srp/ib_srp.c
> +++ b/drivers/infiniband/ulp/srp/ib_srp.c
> @@ -1961,6 +1961,7 @@ static void srp_process_rsp(struct srp_rdma_ch *ch, struct srp_rsp *rsp)
>   		if (scmnd) {
>   			req = scsi_cmd_priv(scmnd);
>   			scmnd = srp_claim_req(ch, req, NULL, scmnd);
> +			scmnd->result = rsp->status;
>   		} else {
>   			shost_printk(KERN_ERR, target->scsi_host,
>   				     "Null scmnd for RSP w/tag %#016llx received on ch %td / QP %#x\n",
> @@ -1972,7 +1973,6 @@ static void srp_process_rsp(struct srp_rdma_ch *ch, struct srp_rsp *rsp)
>   
>   			return;
>   		}
> -		scmnd->result = rsp->status;

What i can see is that we have other places to de-reference scmnd and

scmnd = srp_claim_req(ch, req, NULL, scmnd) is possible to return a NULL to scmnd



Thanks
Zhijian

>   
>   		if (rsp->flags & SRP_RSP_FLAG_SNSVALID) {
>   			memcpy(scmnd->sense_buffer, rsp->data +
                                              ^^^^