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@xxxxxxxxxx>
> >> ---
> >>  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
> >> 
> >> 
>