[PATCH net] net: xfrm: skip policies marked as dead while reinserting policies

[PATCH net] net: xfrm: skip policies marked as dead while reinserting policies

[Dong Chenchen]

BUG: KASAN: slab-use-after-free in xfrm_policy_inexact_list_reinsert+0xb6/0x430
Read of size 1 at addr ffff8881051f3bf8 by task ip/668

CPU: 2 PID: 668 Comm: ip Not tainted 6.5.0-rc5-00182-g25aa0bebba72-dirty #64
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x72/0xa0
 print_report+0xd0/0x620
 kasan_report+0xb6/0xf0
 xfrm_policy_inexact_list_reinsert+0xb6/0x430
 xfrm_policy_inexact_insert_node.constprop.0+0x537/0x800
 xfrm_policy_inexact_alloc_chain+0x23f/0x320
 xfrm_policy_inexact_insert+0x6b/0x590
 xfrm_policy_insert+0x3b1/0x480
 xfrm_add_policy+0x23c/0x3c0
 xfrm_user_rcv_msg+0x2d0/0x510
 netlink_rcv_skb+0x10d/0x2d0
 xfrm_netlink_rcv+0x49/0x60
 netlink_unicast+0x3fe/0x540
 netlink_sendmsg+0x528/0x970
 sock_sendmsg+0x14a/0x160
 ____sys_sendmsg+0x4fc/0x580
 ___sys_sendmsg+0xef/0x160
 __sys_sendmsg+0xf7/0x1b0
 do_syscall_64+0x3f/0x90
 entry_SYSCALL_64_after_hwframe+0x73/0xdd

The root cause is:

cpu 0			cpu1
xfrm_dump_policy
xfrm_policy_walk
list_move_tail
			xfrm_add_policy
			... ...
			xfrm_policy_inexact_list_reinsert
			list_for_each_entry_reverse
				if (!policy->bydst_reinsert)
				//read non-existent policy
xfrm_dump_policy_done
xfrm_policy_walk_done
list_del(&walk->walk.all);

If dump_one_policy() returns err (triggered by netlink socket),
xfrm_policy_walk() will move walk initialized by socket to list
net->xfrm.policy_all. so this socket becomes visible in the global
policy list. The head *walk can be traversed when users add policies
with different prefixlen and trigger xfrm_policy node merge.

It can be fixed by skip such "policies" with walk.dead set to 1.

Fixes: 9cf545ebd591 ("xfrm: policy: store inexact policies in a tree ordered by destination address")
Fixes: 12a169e7d8f4 ("ipsec: Put dumpers on the dump list")
Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com>
---
 net/xfrm/xfrm_policy.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index d6b405782b63..5b56faad78e0 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -848,6 +848,9 @@ static void xfrm_policy_inexact_list_reinsert(struct net *net,
 	matched_d = 0;
 
 	list_for_each_entry_reverse(policy, &net->xfrm.policy_all, walk.all) {
+		if (policy->walk.dead)
+			continue;
+
 		struct hlist_node *newpos = NULL;
 		bool matches_s, matches_d;
 
-- 
2.25.1

Re: [PATCH net] net: xfrm: skip policies marked as dead while reinserting policies

[Leon Romanovsky]

On Mon, Aug 14, 2023 at 09:33:52AM +0800, Dong Chenchen wrote:
> BUG: KASAN: slab-use-after-free in xfrm_policy_inexact_list_reinsert+0xb6/0x430
> Read of size 1 at addr ffff8881051f3bf8 by task ip/668
> 
> CPU: 2 PID: 668 Comm: ip Not tainted 6.5.0-rc5-00182-g25aa0bebba72-dirty #64
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x72/0xa0
>  print_report+0xd0/0x620
>  kasan_report+0xb6/0xf0
>  xfrm_policy_inexact_list_reinsert+0xb6/0x430
>  xfrm_policy_inexact_insert_node.constprop.0+0x537/0x800
>  xfrm_policy_inexact_alloc_chain+0x23f/0x320
>  xfrm_policy_inexact_insert+0x6b/0x590
>  xfrm_policy_insert+0x3b1/0x480
>  xfrm_add_policy+0x23c/0x3c0
>  xfrm_user_rcv_msg+0x2d0/0x510
>  netlink_rcv_skb+0x10d/0x2d0
>  xfrm_netlink_rcv+0x49/0x60
>  netlink_unicast+0x3fe/0x540
>  netlink_sendmsg+0x528/0x970
>  sock_sendmsg+0x14a/0x160
>  ____sys_sendmsg+0x4fc/0x580
>  ___sys_sendmsg+0xef/0x160
>  __sys_sendmsg+0xf7/0x1b0
>  do_syscall_64+0x3f/0x90
>  entry_SYSCALL_64_after_hwframe+0x73/0xdd
> 
> The root cause is:
> 
> cpu 0			cpu1
> xfrm_dump_policy
> xfrm_policy_walk
> list_move_tail
> 			xfrm_add_policy
> 			... ...
> 			xfrm_policy_inexact_list_reinsert
> 			list_for_each_entry_reverse
> 				if (!policy->bydst_reinsert)
> 				//read non-existent policy
> xfrm_dump_policy_done
> xfrm_policy_walk_done
> list_del(&walk->walk.all);
> 
> If dump_one_policy() returns err (triggered by netlink socket),
> xfrm_policy_walk() will move walk initialized by socket to list
> net->xfrm.policy_all. so this socket becomes visible in the global
> policy list. The head *walk can be traversed when users add policies
> with different prefixlen and trigger xfrm_policy node merge.
> 
> It can be fixed by skip such "policies" with walk.dead set to 1.

But where in the xfrm_dump_policy() flow, these policies are becoming to
be walk.dead == 1?

Thanks

> 
> Fixes: 9cf545ebd591 ("xfrm: policy: store inexact policies in a tree ordered by destination address")
> Fixes: 12a169e7d8f4 ("ipsec: Put dumpers on the dump list")
> Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com>
> ---
>  net/xfrm/xfrm_policy.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> index d6b405782b63..5b56faad78e0 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -848,6 +848,9 @@ static void xfrm_policy_inexact_list_reinsert(struct net *net,
>  	matched_d = 0;
>  
>  	list_for_each_entry_reverse(policy, &net->xfrm.policy_all, walk.all) {
> +		if (policy->walk.dead)
> +			continue;
> +
>  		struct hlist_node *newpos = NULL;
>  		bool matches_s, matches_d;
>  
> -- 
> 2.25.1
> 
> 

Re: [PATCH net] net: xfrm: skip policies marked as dead while reinserting policies

[Dong Chenchen]

On Mon, Aug 14, 2023 at 09:33:52AM +0800, Dong Chenchen wrote:
>> BUG: KASAN: slab-use-after-free in xfrm_policy_inexact_list_reinsert+0xb6/0x430
>> Read of size 1 at addr ffff8881051f3bf8 by task ip/668
>> 
>> CPU: 2 PID: 668 Comm: ip Not tainted 6.5.0-rc5-00182-g25aa0bebba72-dirty #64
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13 04/01/2014
>> Call Trace:
>>  <TASK>
>>  dump_stack_lvl+0x72/0xa0
>>  print_report+0xd0/0x620
>>  kasan_report+0xb6/0xf0
>>  xfrm_policy_inexact_list_reinsert+0xb6/0x430
>>  xfrm_policy_inexact_insert_node.constprop.0+0x537/0x800
>>  xfrm_policy_inexact_alloc_chain+0x23f/0x320
>>  xfrm_policy_inexact_insert+0x6b/0x590
>>  xfrm_policy_insert+0x3b1/0x480
>>  xfrm_add_policy+0x23c/0x3c0
>>  xfrm_user_rcv_msg+0x2d0/0x510
>>  netlink_rcv_skb+0x10d/0x2d0
>>  xfrm_netlink_rcv+0x49/0x60
>>  netlink_unicast+0x3fe/0x540
>>  netlink_sendmsg+0x528/0x970
>>  sock_sendmsg+0x14a/0x160
>>  ____sys_sendmsg+0x4fc/0x580
>>  ___sys_sendmsg+0xef/0x160
>>  __sys_sendmsg+0xf7/0x1b0
>>  do_syscall_64+0x3f/0x90
>>  entry_SYSCALL_64_after_hwframe+0x73/0xdd
>> 
>> The root cause is:
>> 
>> cpu 0			cpu1
>> xfrm_dump_policy
>> xfrm_policy_walk
>> list_move_tail
>> 			xfrm_add_policy
>> 			... ...
>> 			xfrm_policy_inexact_list_reinsert
>> 			list_for_each_entry_reverse
>> 				if (!policy->bydst_reinsert)
>> 				//read non-existent policy
>> xfrm_dump_policy_done
>> xfrm_policy_walk_done
>> list_del(&walk->walk.all);
>> 
>> If dump_one_policy() returns err (triggered by netlink socket),
>> xfrm_policy_walk() will move walk initialized by socket to list
>> net->xfrm.policy_all. so this socket becomes visible in the global
>> policy list. The head *walk can be traversed when users add policies
>> with different prefixlen and trigger xfrm_policy node merge.
>> 
>> It can be fixed by skip such "policies" with walk.dead set to 1.
>
>But where in the xfrm_dump_policy() flow, these policies are becoming to
>be walk.dead == 1?
>
>Thanks
>
user will use xfrm_dispatch[XFRM_MSG_GETPOLICY] ops to get xfrm policy.
	
	.start = xfrm_dump_policy_start

xfrm_dump_policy_start() will set walk.dead to 1 by call 
xfrm_policy_walk_init().

Thanks
>> 
>> Fixes: 9cf545ebd591 ("xfrm: policy: store inexact policies in a tree ordered by destination address")
>> Fixes: 12a169e7d8f4 ("ipsec: Put dumpers on the dump list")
>> Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com>
>> ---
>>  net/xfrm/xfrm_policy.c | 3 +++
>>  1 file changed, 3 insertions(+)
>> 
>> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
>> index d6b405782b63..5b56faad78e0 100644
>> --- a/net/xfrm/xfrm_policy.c
>> +++ b/net/xfrm/xfrm_policy.c
>> @@ -848,6 +848,9 @@ static void xfrm_policy_inexact_list_reinsert(struct net *net,
>>  	matched_d = 0;
>>  
>>  	list_for_each_entry_reverse(policy, &net->xfrm.policy_all, walk.all) {
>> +		if (policy->walk.dead)
>> +			continue;
>> +
>>  		struct hlist_node *newpos = NULL;
>>  		bool matches_s, matches_d;
>>  
>> -- 
>> 2.25.1
>> 
>> 

Re: [PATCH net] net: xfrm: skip policies marked as dead while reinserting policies

[Leon Romanovsky]

On Mon, Aug 14, 2023 at 04:58:46PM +0800, Dong Chenchen wrote:
> On Mon, Aug 14, 2023 at 09:33:52AM +0800, Dong Chenchen wrote:
> >> BUG: KASAN: slab-use-after-free in xfrm_policy_inexact_list_reinsert+0xb6/0x430
> >> Read of size 1 at addr ffff8881051f3bf8 by task ip/668
> >> 
> >> CPU: 2 PID: 668 Comm: ip Not tainted 6.5.0-rc5-00182-g25aa0bebba72-dirty #64
> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13 04/01/2014
> >> Call Trace:
> >>  <TASK>
> >>  dump_stack_lvl+0x72/0xa0
> >>  print_report+0xd0/0x620
> >>  kasan_report+0xb6/0xf0
> >>  xfrm_policy_inexact_list_reinsert+0xb6/0x430
> >>  xfrm_policy_inexact_insert_node.constprop.0+0x537/0x800
> >>  xfrm_policy_inexact_alloc_chain+0x23f/0x320
> >>  xfrm_policy_inexact_insert+0x6b/0x590
> >>  xfrm_policy_insert+0x3b1/0x480
> >>  xfrm_add_policy+0x23c/0x3c0
> >>  xfrm_user_rcv_msg+0x2d0/0x510
> >>  netlink_rcv_skb+0x10d/0x2d0
> >>  xfrm_netlink_rcv+0x49/0x60
> >>  netlink_unicast+0x3fe/0x540
> >>  netlink_sendmsg+0x528/0x970
> >>  sock_sendmsg+0x14a/0x160
> >>  ____sys_sendmsg+0x4fc/0x580
> >>  ___sys_sendmsg+0xef/0x160
> >>  __sys_sendmsg+0xf7/0x1b0
> >>  do_syscall_64+0x3f/0x90
> >>  entry_SYSCALL_64_after_hwframe+0x73/0xdd
> >> 
> >> The root cause is:
> >> 
> >> cpu 0			cpu1
> >> xfrm_dump_policy
> >> xfrm_policy_walk
> >> list_move_tail
> >> 			xfrm_add_policy
> >> 			... ...
> >> 			xfrm_policy_inexact_list_reinsert
> >> 			list_for_each_entry_reverse
> >> 				if (!policy->bydst_reinsert)
> >> 				//read non-existent policy
> >> xfrm_dump_policy_done
> >> xfrm_policy_walk_done
> >> list_del(&walk->walk.all);
> >> 
> >> If dump_one_policy() returns err (triggered by netlink socket),
> >> xfrm_policy_walk() will move walk initialized by socket to list
> >> net->xfrm.policy_all. so this socket becomes visible in the global
> >> policy list. The head *walk can be traversed when users add policies
> >> with different prefixlen and trigger xfrm_policy node merge.
> >> 
> >> It can be fixed by skip such "policies" with walk.dead set to 1.
> >
> >But where in the xfrm_dump_policy() flow, these policies are becoming to
> >be walk.dead == 1?
> >
> >Thanks
> >
> user will use xfrm_dispatch[XFRM_MSG_GETPOLICY] ops to get xfrm policy.
> 	
> 	.start = xfrm_dump_policy_start
> 
> xfrm_dump_policy_start() will set walk.dead to 1 by call 
> xfrm_policy_walk_init().

Thanks

> 
> Thanks
> >> 
> >> Fixes: 9cf545ebd591 ("xfrm: policy: store inexact policies in a tree ordered by destination address")
> >> Fixes: 12a169e7d8f4 ("ipsec: Put dumpers on the dump list")
> >> Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com>
> >> ---
> >>  net/xfrm/xfrm_policy.c | 3 +++
> >>  1 file changed, 3 insertions(+)
> >> 
> >> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> >> index d6b405782b63..5b56faad78e0 100644
> >> --- a/net/xfrm/xfrm_policy.c
> >> +++ b/net/xfrm/xfrm_policy.c
> >> @@ -848,6 +848,9 @@ static void xfrm_policy_inexact_list_reinsert(struct net *net,
> >>  	matched_d = 0;
> >>  
> >>  	list_for_each_entry_reverse(policy, &net->xfrm.policy_all, walk.all) {
> >> +		if (policy->walk.dead)
> >> +			continue;
> >> +
> >>  		struct hlist_node *newpos = NULL;
> >>  		bool matches_s, matches_d;
> >>  
> >> -- 
> >> 2.25.1
> >> 
> >> 
> 

Re: [PATCH net] net: xfrm: skip policies marked as dead while reinserting policies

[Leon Romanovsky]

On Mon, Aug 14, 2023 at 09:33:52AM +0800, Dong Chenchen wrote:
> BUG: KASAN: slab-use-after-free in xfrm_policy_inexact_list_reinsert+0xb6/0x430
> Read of size 1 at addr ffff8881051f3bf8 by task ip/668
> 
> CPU: 2 PID: 668 Comm: ip Not tainted 6.5.0-rc5-00182-g25aa0bebba72-dirty #64
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x72/0xa0
>  print_report+0xd0/0x620
>  kasan_report+0xb6/0xf0
>  xfrm_policy_inexact_list_reinsert+0xb6/0x430
>  xfrm_policy_inexact_insert_node.constprop.0+0x537/0x800
>  xfrm_policy_inexact_alloc_chain+0x23f/0x320
>  xfrm_policy_inexact_insert+0x6b/0x590
>  xfrm_policy_insert+0x3b1/0x480
>  xfrm_add_policy+0x23c/0x3c0
>  xfrm_user_rcv_msg+0x2d0/0x510
>  netlink_rcv_skb+0x10d/0x2d0
>  xfrm_netlink_rcv+0x49/0x60
>  netlink_unicast+0x3fe/0x540
>  netlink_sendmsg+0x528/0x970
>  sock_sendmsg+0x14a/0x160
>  ____sys_sendmsg+0x4fc/0x580
>  ___sys_sendmsg+0xef/0x160
>  __sys_sendmsg+0xf7/0x1b0
>  do_syscall_64+0x3f/0x90
>  entry_SYSCALL_64_after_hwframe+0x73/0xdd
> 
> The root cause is:
> 
> cpu 0			cpu1
> xfrm_dump_policy
> xfrm_policy_walk
> list_move_tail
> 			xfrm_add_policy
> 			... ...
> 			xfrm_policy_inexact_list_reinsert
> 			list_for_each_entry_reverse
> 				if (!policy->bydst_reinsert)
> 				//read non-existent policy
> xfrm_dump_policy_done
> xfrm_policy_walk_done
> list_del(&walk->walk.all);
> 
> If dump_one_policy() returns err (triggered by netlink socket),
> xfrm_policy_walk() will move walk initialized by socket to list
> net->xfrm.policy_all. so this socket becomes visible in the global
> policy list. The head *walk can be traversed when users add policies
> with different prefixlen and trigger xfrm_policy node merge.
> 
> It can be fixed by skip such "policies" with walk.dead set to 1.
> 
> Fixes: 9cf545ebd591 ("xfrm: policy: store inexact policies in a tree ordered by destination address")
> Fixes: 12a169e7d8f4 ("ipsec: Put dumpers on the dump list")
> Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com>
> ---
>  net/xfrm/xfrm_policy.c | 3 +++
>  1 file changed, 3 insertions(+)
> 

Thanks,
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>

Re: [PATCH net] net: xfrm: skip policies marked as dead while reinserting policies

[Florian Westphal]

Dong Chenchen <dongchenchen2@huawei.com> wrote:
> BUG: KASAN: slab-use-after-free in xfrm_policy_inexact_list_reinsert+0xb6/0x430
> Read of size 1 at addr ffff8881051f3bf8 by task ip/668
> 
> CPU: 2 PID: 668 Comm: ip Not tainted 6.5.0-rc5-00182-g25aa0bebba72-dirty #64
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x72/0xa0
>  print_report+0xd0/0x620
>  kasan_report+0xb6/0xf0
>  xfrm_policy_inexact_list_reinsert+0xb6/0x430
>  xfrm_policy_inexact_insert_node.constprop.0+0x537/0x800
>  xfrm_policy_inexact_alloc_chain+0x23f/0x320
>  xfrm_policy_inexact_insert+0x6b/0x590
>  xfrm_policy_insert+0x3b1/0x480
>  xfrm_add_policy+0x23c/0x3c0
>  xfrm_user_rcv_msg+0x2d0/0x510
>  netlink_rcv_skb+0x10d/0x2d0
>  xfrm_netlink_rcv+0x49/0x60
>  netlink_unicast+0x3fe/0x540
>  netlink_sendmsg+0x528/0x970
>  sock_sendmsg+0x14a/0x160
>  ____sys_sendmsg+0x4fc/0x580
>  ___sys_sendmsg+0xef/0x160
>  __sys_sendmsg+0xf7/0x1b0
>  do_syscall_64+0x3f/0x90
>  entry_SYSCALL_64_after_hwframe+0x73/0xdd
> 
> The root cause is:
> 
> cpu 0			cpu1
> xfrm_dump_policy
> xfrm_policy_walk
> list_move_tail
> 			xfrm_add_policy
> 			... ...
> 			xfrm_policy_inexact_list_reinsert
> 			list_for_each_entry_reverse
> 				if (!policy->bydst_reinsert)
> 				//read non-existent policy
> xfrm_dump_policy_done
> xfrm_policy_walk_done
> list_del(&walk->walk.all);
> 
> If dump_one_policy() returns err (triggered by netlink socket),
> xfrm_policy_walk() will move walk initialized by socket to list
> net->xfrm.policy_all. so this socket becomes visible in the global
> policy list. The head *walk can be traversed when users add policies
> with different prefixlen and trigger xfrm_policy node merge.
> 
> It can be fixed by skip such "policies" with walk.dead set to 1.
> 
> Fixes: 9cf545ebd591 ("xfrm: policy: store inexact policies in a tree ordered by destination address")
> Fixes: 12a169e7d8f4 ("ipsec: Put dumpers on the dump list")
> Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com>
> ---
>  net/xfrm/xfrm_policy.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> index d6b405782b63..5b56faad78e0 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -848,6 +848,9 @@ static void xfrm_policy_inexact_list_reinsert(struct net *net,
>  	matched_d = 0;
>  
>  	list_for_each_entry_reverse(policy, &net->xfrm.policy_all, walk.all) {
> +		if (policy->walk.dead)
> +			continue;
> +

Looks like we have other places that might trigger a splat, e.g.:

1816 int xfrm_policy_flush(struct net *net, u8 type, bool task_valid)
..
1827 again:
1828         list_for_each_entry(pol, &net->xfrm.policy_all, walk.all) {
1829                 dir = xfrm_policy_id2dir(pol->index);
1830                 if (pol->walk.dead ||
1831                     dir >= XFRM_POLICY_MAX ||

'walker' has no pol->index, so I suspect this would trigger a kasan splat as well,
this needs to check walk.dead before access to pol->index.

Re: [PATCH net] net: xfrm: skip policies marked as dead while reinserting policies

[Dong Chenchen]

Dong Chenchen <dongchenchen2@huawei.com> wrote:
>> BUG: KASAN: slab-use-after-free in xfrm_policy_inexact_list_reinsert+0xb6/0x430
>> Read of size 1 at addr ffff8881051f3bf8 by task ip/668
>> 
>> CPU: 2 PID: 668 Comm: ip Not tainted 6.5.0-rc5-00182-g25aa0bebba72-dirty #64
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13 04/01/2014
>> Call Trace:
>>  <TASK>
>>  dump_stack_lvl+0x72/0xa0
>>  print_report+0xd0/0x620
>>  kasan_report+0xb6/0xf0
>>  xfrm_policy_inexact_list_reinsert+0xb6/0x430
>>  xfrm_policy_inexact_insert_node.constprop.0+0x537/0x800
>>  xfrm_policy_inexact_alloc_chain+0x23f/0x320
>>  xfrm_policy_inexact_insert+0x6b/0x590
>>  xfrm_policy_insert+0x3b1/0x480
>>  xfrm_add_policy+0x23c/0x3c0
>>  xfrm_user_rcv_msg+0x2d0/0x510
>>  netlink_rcv_skb+0x10d/0x2d0
>>  xfrm_netlink_rcv+0x49/0x60
>>  netlink_unicast+0x3fe/0x540
>>  netlink_sendmsg+0x528/0x970
>>  sock_sendmsg+0x14a/0x160
>>  ____sys_sendmsg+0x4fc/0x580
>>  ___sys_sendmsg+0xef/0x160
>>  __sys_sendmsg+0xf7/0x1b0
>>  do_syscall_64+0x3f/0x90
>>  entry_SYSCALL_64_after_hwframe+0x73/0xdd
>> 
>> The root cause is:
>> 
>> cpu 0			cpu1
>> xfrm_dump_policy
>> xfrm_policy_walk
>> list_move_tail
>> 			xfrm_add_policy
>> 			... ...
>> 			xfrm_policy_inexact_list_reinsert
>> 			list_for_each_entry_reverse
>> 				if (!policy->bydst_reinsert)
>> 				//read non-existent policy
>> xfrm_dump_policy_done
>> xfrm_policy_walk_done
>> list_del(&walk->walk.all);
>> 
>> If dump_one_policy() returns err (triggered by netlink socket),
>> xfrm_policy_walk() will move walk initialized by socket to list
>> net->xfrm.policy_all. so this socket becomes visible in the global
>> policy list. The head *walk can be traversed when users add policies
>> with different prefixlen and trigger xfrm_policy node merge.
>> 
>> It can be fixed by skip such "policies" with walk.dead set to 1.
>> 
>> Fixes: 9cf545ebd591 ("xfrm: policy: store inexact policies in a tree ordered by destination address")
>> Fixes: 12a169e7d8f4 ("ipsec: Put dumpers on the dump list")
>> Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com>
>> ---
>>  net/xfrm/xfrm_policy.c | 3 +++
>>  1 file changed, 3 insertions(+)
>> 
>> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
>> index d6b405782b63..5b56faad78e0 100644
>> --- a/net/xfrm/xfrm_policy.c
>> +++ b/net/xfrm/xfrm_policy.c
>> @@ -848,6 +848,9 @@ static void xfrm_policy_inexact_list_reinsert(struct net *net,
>>  	matched_d = 0;
>>  
>>  	list_for_each_entry_reverse(policy, &net->xfrm.policy_all, walk.all) {
>> +		if (policy->walk.dead)
>> +			continue;
>> +
>
>Looks like we have other places that might trigger a splat, e.g.:
>
>1816 int xfrm_policy_flush(struct net *net, u8 type, bool task_valid)
>..
>1827 again:
>1828         list_for_each_entry(pol, &net->xfrm.policy_all, walk.all) {
>1829                 dir = xfrm_policy_id2dir(pol->index);
>1830                 if (pol->walk.dead ||
>1831                     dir >= XFRM_POLICY_MAX ||
>
>'walker' has no pol->index, so I suspect this would trigger a kasan splat as well,
>this needs to check walk.dead before access to pol->index.
Yes, you are right. xfrm_hash_rebuild(),xfrm_dev_policy_flush() might also trigger
similar bug. xfrm_policy_walk() add "walker" to list tail and these func use 
list_for_each_entry() to traverse list.So it is unlikely to trigger the bug.

But there's still possible, i will fix it in v2.

Thanks!