Messages in this thread | | | Date | Tue, 15 Aug 2023 12:13:24 +0300 | From | Leon Romanovsky <> | Subject | Re: [Patch net, v2] net: xfrm: skip policies marked as dead while reinserting policies |
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On Tue, Aug 15, 2023 at 04:47:58PM +0800, Dong Chenchen wrote: > 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@huawei.com> > >> --- > >> v2: fix similiar similar while rehashing and flushing policies > >> --- > >> net/xfrm/xfrm_policy.c | 20 +++++++++++++++----- > >> 1 file changed, 15 insertions(+), 5 deletions(-)
<...>
> >> @@ -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.
But all operations here are an outcome of "list_for_each_entry(policy, &net->xfrm.policy_all, walk.all)" which stores in policy iterator the pointer to struct xfrm_policy.
How at the same time access to policy->walk.dead is valid while policy->index is not?
Thanks
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