netdev - Re: [Patch net, v2] net: xfrm: skip policies marked as dead while reinserting policies

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Message-ID: <20230815060026.GE22185@unreal>
Date: Tue, 15 Aug 2023 16:47:58 +0800
From: Dong Chenchen <dongchenchen2@...wei.com>
To: <leon@...nel.org>
CC: <fw@...len.de>, <steffen.klassert@...unet.com>,
	<herbert@...dor.apana.org.au>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <timo.teras@....fi>,
	<yuehaibing@...wei.com>, <weiyongjun1@...wei.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Patch net, v2] net: xfrm: skip policies marked as dead while reinserting policies

On Mon, Aug 14, 2023 at 10:00:13PM +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.
>> 
>> The issue can also be triggered by policy list traversal while rehashing
>> and flushing policies.
>> 
>> 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@...wei.com>
>> ---
>> v2: fix similiar similar while rehashing and flushing policies
>> ---
>>  net/xfrm/xfrm_policy.c | 20 +++++++++++++++-----
>>  1 file changed, 15 insertions(+), 5 deletions(-)
>> 
>> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
>> index d6b405782b63..33efd46fb291 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;
>
>You can't declare new variables in the middle of execution scope in C.
Thank you for your suggestions. I will fix it in v3.
>
>>  
>> @@ -1253,11 +1256,14 @@ static void xfrm_hash_rebuild(struct work_struct *work)
>>  	 * we start with destructive action.
>>  	 */
>>  	list_for_each_entry(policy, &net->xfrm.policy_all, walk.all) {
>> +		if (policy->walk.dead)
>> +			continue;
>> +
>>  		struct xfrm_pol_inexact_bin *bin;
>>  		u8 dbits, sbits;
>
>Same comment as above.
>
>>  
>>  		dir = xfrm_policy_id2dir(policy->index);
>> -		if (policy->walk.dead || dir >= XFRM_POLICY_MAX)
>> +		if (dir >= XFRM_POLICY_MAX)
>
>This change is unnecessary, previous code was perfectly fine.
>
The walker object initialized by xfrm_policy_walk_init() doesnt have policy. 
list_for_each_entry() will use the walker offset to calculate policy address.
It's nonexistent and different from invalid dead policy. It will read memory 
that doesnt belong to walker if dereference policy->index.
I think we should protect the memory.

Thanks
>>  			continue;
>>  
>>  		if ((dir & XFRM_POLICY_MASK) == XFRM_POLICY_OUT) {
>> @@ -1823,9 +1829,11 @@ int xfrm_policy_flush(struct net *net, u8 type, bool task_valid)
>>  
>>  again:
>>  	list_for_each_entry(pol, &net->xfrm.policy_all, walk.all) {
>> +		if (pol->walk.dead)
>> +			continue;
>> +
>>  		dir = xfrm_policy_id2dir(pol->index);
>> -		if (pol->walk.dead ||
>> -		    dir >= XFRM_POLICY_MAX ||
>> +		if (dir >= XFRM_POLICY_MAX ||
>
>This change is unnecessary, previous code was perfectly fine.
>
>>  		    pol->type != type)
>>  			continue;
>>  
>> @@ -1862,9 +1870,11 @@ int xfrm_dev_policy_flush(struct net *net, struct net_device *dev,
>>  
>>  again:
>>  	list_for_each_entry(pol, &net->xfrm.policy_all, walk.all) {
>> +		if (pol->walk.dead)
>> +			continue;
>> +
>>  		dir = xfrm_policy_id2dir(pol->index);
>> -		if (pol->walk.dead ||
>> -		    dir >= XFRM_POLICY_MAX ||
>> +		if (dir >= XFRM_POLICY_MAX ||
>>  		    pol->xdo.dev != dev)
>>  			continue;
>
>Ditto.
>
>>  
>> -- 
>> 2.25.1
>>