[PATCH v2] scsi: avoid potential deadloop in iscsi_if_rx func

[PATCH v2] scsi: avoid potential deadloop in iscsi_if_rx func

[wubo (T)]

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_msg = 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>
Suggested-by: Lee Duncan <LDuncan@suse.com>

---
 drivers/scsi/scsi_transport_iscsi.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/scsi/scsi_transport_iscsi.c b/drivers/scsi/scsi_transport_iscsi.c
index 417b868d8735..85482bcfc727 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) || @@ -3710,6 +3713,16 @@ iscsi_if_rx(struct sk_buff *skb)
 				break;
 			if (ev->type == ISCSI_UEVENT_GET_CHAP && !err)
 				break;
+			/*
+			 * special case for sending reply failed too many times,
+			 * on error - fall through.
+			 */
+			if (--retries < 0) {
+				printk(KERN_ERR "Send reply failed too many times. "
+				       "Max supported retries %u\n", ISCSI_SEND_MAX_ALLOWED);
+				break;
+			}
+
 			err = iscsi_if_send_reply(portid, nlh->nlmsg_type,
 						  ev, sizeof(*ev));
 		} while (err < 0 && err != -ECONNREFUSED && err != -ESRCH);
--
1.8.3.1

Antw: [PATCH v2] scsi: avoid potential deadloop in iscsi_if_rx func

[Ulrich Windl]

>>> "wubo (T)" <wubo40@huawei.com> schrieb am 30.10.2019 um 08:56 in Nachricht
<EDBAAA0BBBA2AC4E9C8B6B81DEEE1D6915DFA0FE@dggeml505-mbs.china.huawei.com>:
> From: Bo Wu <wubo40@huawei.com>

...
> +			if (--retries < 0) {
> +				printk(KERN_ERR "Send reply failed too many times. "
> +				       "Max supported retries %u\n", ISCSI_SEND_MAX_ALLOWED);

Just for "personal taste": Why not simplify the message to:?
+				printk(KERN_ERR "Send reply failed too many times (%u)\n",
                               ISCSI_SEND_MAX_ALLOWED);

> +				break;
> +			}
> +

Maybe place the number after "many" as an alternative. I think as the message is expected to be rare, a short variant is justified.
Also one could discuss wether the problem that originates "from external" should be KERN_ERR, or maybe just a warning, because the kernel itself can do little against that problem, and it's not a "kernel error" after all ;-)

Regards,
Ulrich

Antw: [PATCH v2] scsi: avoid potential deadloop in iscsi_if_rx func

[wubo (T)]

> >>> "wubo (T)" <wubo40@huawei.com> schrieb am 30.10.2019 um 08:56 in
> Nachricht
> <EDBAAA0BBBA2AC4E9C8B6B81DEEE1D6915DFA0FE@dggeml505-mbs.china.
> huawei.com>:
> > From: Bo Wu <wubo40@huawei.com>
> 
> ...
> > +			if (--retries < 0) {
> > +				printk(KERN_ERR "Send reply failed too many times. "
> > +				       "Max supported retries %u\n",
> ISCSI_SEND_MAX_ALLOWED);
> 
> Just for "personal taste": Why not simplify the message to:?
> +				printk(KERN_ERR "Send reply failed too many times
> (%u)\n",
>                                ISCSI_SEND_MAX_ALLOWED);
> 
> > +				break;
> > +			}
> > +
> 
> Maybe place the number after "many" as an alternative. I think as the
> message is expected to be rare, a short variant is justified.

Thanks for your suggestion. This problem occured when iscsi_if_send_reply returns -EAGAIN.
Consider possible other anomalies scenes. In order to get diagnostic information, it is better to replace "many" with error code.

Modify as follow:
if (--retries < 0) {
	printk(KERN_WARNING "Send reply failed, error %d\n", err);
	break;
}

> Also one could discuss wether the problem that originates "from external"
> should be KERN_ERR, or maybe just a warning, because the kernel itself can do
> little against that problem, and it's not a "kernel error" after all ;-)

You are right, This problem scene rarely appears .it is friendly to replace the error with warning.

> 
> Regards,
> Ulrich
> 
> 
> 

Thanks,
Bo Wu