Re: [PATCH] scsi: avoid potential deadloop in iscsi_if_rx func

[Lee Duncan <LDuncan@suse.com>]

On 10/26/19 1:55 AM, wubo (T) wrote:
> From: Bo Wu <wubo40@huawei.com>
> 
> In iscsi_if_rx func, after receiving one request through iscsi_if_recv_msg
> func,iscsi_if_send_reply will be called to try to reply the request in 
> do-loop. If the return of iscsi_if_send_reply func fails all the time, one
> deadloop will occur.
>  
> For example, a client only send msg without calling recvmsg func, then it
> will result in the watchdog soft lockup. The details are given as follows,
> 
> Details of the special case which can cause deadloop:
> sock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ISCSI); 
> ... 
> retval = bind(sock_fd, (struct sock addr*) & src_addr, sizeof (src_addr); 
> ... 
> while (1) { 
> 	state_smg = sendmsg(sock_fd, &msg, 0); 
> } 
> // Note: recvmsg (sock_fd, & msg, 0) is not processed here. 
> close(sock_fd); 
> 
> watchdog: BUG: soft lockup - CPU#7 stuck for 22s! [netlink_test:253305]
> Sample time: 4000897528 ns(HZ: 250)
> Sample stat: 
> curr: user: 675503481560, nice: 321724050, sys: 448689506750, idle: 4654054240530, iowait: 40885550700, irq: 14161174020, softirq: 8104324140, st: 0
> deta: user: 0, nice: 0, sys: 3998210100, idle: 0, iowait: 0, irq: 1547170, softirq: 242870, st: 0
> Sample softirq:
> 	TIMER:        992
> 	SCHED:          8
> Sample irqstat:
>  irq    2: delta       1003, curr:    3103802, arch_timer
> CPU: 7 PID: 253305 Comm: netlink_test Kdump: loaded Tainted: G           OE     
> Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
> pstate: 40400005 (nZcv daif +PAN -UAO)
> pc : __alloc_skb+0x104/0x1b0
> lr : __alloc_skb+0x9c/0x1b0
> sp : ffff000033603a30
> x29: ffff000033603a30 x28: 00000000000002dd 
> x27: ffff800b34ced810 x26: ffff800ba7569f00 
> x25: 00000000ffffffff x24: 0000000000000000 
> x23: ffff800f7c43f600 x22: 0000000000480020 
> x21: ffff0000091d9000 x20: ffff800b34eff200 
> x19: ffff800ba7569f00 x18: 0000000000000000 
> x17: 0000000000000000 x16: 0000000000000000 
> x15: 0000000000000000 x14: 0001000101000100 
> x13: 0000000101010000 x12: 0101000001010100 
> x11: 0001010101010001 x10: 00000000000002dd 
> x9 : ffff000033603d58 x8 : ffff800b34eff400 
> x7 : ffff800ba7569200 x6 : ffff800b34eff400 
> x5 : 0000000000000000 x4 : 00000000ffffffff 
> x3 : 0000000000000000 x2 : 0000000000000001 
> x1 : ffff800b34eff2c0 x0 : 0000000000000300 
> Call trace:
> __alloc_skb+0x104/0x1b0
> iscsi_if_rx+0x144/0x12bc [scsi_transport_iscsi]
> netlink_unicast+0x1e0/0x258
> netlink_sendmsg+0x310/0x378
> sock_sendmsg+0x4c/0x70
> sock_write_iter+0x90/0xf0
> __vfs_write+0x11c/0x190
> vfs_write+0xac/0x1c0
> ksys_write+0x6c/0xd8
> __arm64_sys_write+0x24/0x30
> el0_svc_common+0x78/0x130
> el0_svc_handler+0x38/0x78
> el0_svc+0x8/0xc
> 
> Here, we add one limit of retry times in do-loop to avoid the deadloop.
> 
> Signed-off-by: Bo Wu <wubo40@huawei.com>
> Reviewed-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
> ---
>  drivers/scsi/scsi_transport_iscsi.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_transport_iscsi.c b/drivers/scsi/scsi_transport_iscsi.c
> index 417b868d8735..f377bfed6b0c 100644
> --- a/drivers/scsi/scsi_transport_iscsi.c
> +++ b/drivers/scsi/scsi_transport_iscsi.c
> @@ -24,6 +24,8 @@
>  
>  #define ISCSI_TRANSPORT_VERSION "2.0-870"
>  
> +#define ISCSI_SEND_MAX_ALLOWED     10
> +
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/iscsi.h>
>  
> @@ -3682,6 +3684,7 @@ iscsi_if_rx(struct sk_buff *skb)
>  		struct nlmsghdr	*nlh;
>  		struct iscsi_uevent *ev;
>  		uint32_t group;
> +		int retries = ISCSI_SEND_MAX_ALLOWED;
>  
>  		nlh = nlmsg_hdr(skb);
>  		if (nlh->nlmsg_len < sizeof(*nlh) + sizeof(*ev) ||
> @@ -3710,8 +3713,11 @@ iscsi_if_rx(struct sk_buff *skb)
>  				break;
>  			if (ev->type == ISCSI_UEVENT_GET_CHAP && !err)
>  				break;
> +			if (retries <= 0)
> +				break;
>  			err = iscsi_if_send_reply(portid, nlh->nlmsg_type,
>  						  ev, sizeof(*ev));
> +			retries--;
>  		} while (err < 0 && err != -ECONNREFUSED && err != -ESRCH);
>  		skb_pull(skb, rlen);
>  	}
> 

You could have used "if (--retries < 0)" (or some variation thereof) but
that may not be as clear, and certainly is only a nit. So I'm fine with
that.

But I would like to see some sort of error or even debug kernel message
if we time out waiting to receive a response. Otherwise, how will some
human diagnose this problem?

-- 
Lee Duncan