From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.netfilter.org (mail.netfilter.org [217.70.190.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 387AD4A02; Sun, 8 Mar 2026 10:46:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.70.190.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772966785; cv=none; b=jLfXrP94/JqUvcyLFb4pdBYytL4eK1K+5Z1mYDHA7y+uEQiV1SEzxEiC3ltYe1Benp/XFfOeMNpb53j0kFeUl3x2aayWxHFHlYWwApJIh8P2a8cBSiEFCFPxvLa46J7a9ROZviwVuIYoQVv9aog5GSIKd9nyugfMthVRFWMqQ/E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772966785; c=relaxed/simple; bh=YP1Oa2fDXHorc7Eu0+C6ijFA2CUJVHcJ5jOZHEVxTyg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jVW+fxJ6eBsaLJs5vS/2heAfpQ5wzks5E2iofUVXTNeSj3oqnfHfmcmRCbVLW3e3gFYO/jnU5kIAJOR405iqb30bClS9JwLd9VZ36LvB6caPYVHGG9963akoFdeI6cIG5mr2o5yiIDEn+OSNVaFcp4Xwas2uUt+j49MT84v16hM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=netfilter.org; spf=pass smtp.mailfrom=netfilter.org; dkim=pass (2048-bit key) header.d=netfilter.org header.i=@netfilter.org header.b=lbnor7lA; arc=none smtp.client-ip=217.70.190.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=netfilter.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=netfilter.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=netfilter.org header.i=@netfilter.org header.b="lbnor7lA" Received: from netfilter.org (mail-agni [217.70.190.124]) by mail.netfilter.org (Postfix) with UTF8SMTPSA id CEE3A60338; Sun, 8 Mar 2026 11:46:21 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=netfilter.org; s=2025; t=1772966781; bh=kOHk9G53xuNeeSNXfbFpGJnMSZBLkYtMEuo30MxxD4o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=lbnor7lAiERPJu8ykpaVLxNeQsvNPeN6LA+pOhmDpzdkRHTHnduLTTtVTs9QP2RcW Y07WiPuIcpxPFnZSm3jJV1o2Bls7OTaJ97MgvDHRgyJaq/5ICtszPR99HDZ9MLfWOp 8/p54tFTp4tyBjwkGMt0fN8kUI2C0apHTUWLiTfQ+RK+Ig7vlBQQYRmLyCrVvnu7N5 b6E/kb59AJFr/67c7ydSsugVJfkXlND6fePdZVv+pMs+CW1Ha6BOIZu5HzRc/tjUFT /tBrXteRU8mSyku9BFelOF9SKRJ1exI098cQpsbxFqVNLvj1RiNUHp9bnravFhe0SM mLWuibs2rONmA== Date: Sun, 8 Mar 2026 11:46:19 +0100 From: Pablo Neira Ayuso To: Hyunwoo Kim Cc: fw@strlen.de, phil@nwl.cc, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org Subject: Re: [PATCH net] netfilter: ctnetlink: fix use-after-free of exp->master in single expectation GET Message-ID: References: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On Sun, Mar 08, 2026 at 02:21:10AM +0900, Hyunwoo Kim wrote: > ctnetlink_get_expect() in the non-dump path calls > nf_ct_expect_find_get() which only takes a reference on the expectation > itself, not on exp->master. It then calls ctnetlink_exp_fill_info() > which dereferences exp->master extensively (tuplehash, ct->ext via > nfct_help()). > > A concurrent conntrack deletion through NFNL_SUBSYS_CTNETLINK (a > different nfnetlink subsystem mutex than NFNL_SUBSYS_CTNETLINK_EXP) can > free the master conntrack while the single GET is in progress, leading > to use-after-free. In particular, kfree(ct->ext) is immediate and not > RCU-deferred. > > Fix this by taking a reference on exp->master under rcu_read_lock > (required for SLAB_TYPESAFE_BY_RCU) before calling > ctnetlink_exp_fill_info() and releasing it afterwards. > > KASAN report: > > [ 6.526107] ================================================================== > [ 6.526345] BUG: KASAN: slab-use-after-free in ctnetlink_dump_tuples_ip+0xbc/0x1f0 Please, fix this with in the same patch, I suggest you call this patch: netfilter: ctnetlink: hold reference on master conntrack when dumping expectation it is the same class of bug. Thanks > [ 6.526570] Read of size 2 at addr ffff8881042a8cb2 by task poc3/134 > [ 6.526745] > [ 6.526798] CPU: 0 UID: 0 PID: 134 Comm: poc3 Not tainted 7.0.0-rc2+ #6 PREEMPTLAZY > [ 6.526801] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 > [ 6.526805] Call Trace: > [ 6.526808] > [ 6.526809] dump_stack_lvl+0x64/0x80 > [ 6.526821] print_report+0xce/0x660 > [ 6.526828] ? __pfx__raw_spin_lock_irqsave+0x10/0x10 > [ 6.526836] ? kasan_save_stack+0x33/0x60 > [ 6.526841] ? __virt_addr_valid+0xef/0x1a0 > [ 6.526848] ? ctnetlink_dump_tuples_ip+0xbc/0x1f0 > [ 6.526850] kasan_report+0xce/0x100 > [ 6.526852] ? ctnetlink_dump_tuples_ip+0xbc/0x1f0 > [ 6.526855] ctnetlink_dump_tuples_ip+0xbc/0x1f0 > [ 6.526858] ? __pfx_ctnetlink_dump_tuples_ip+0x10/0x10 > [ 6.526860] ? ctnetlink_dump_tuples_proto+0x144/0x190 > [ 6.526862] ? skb_put+0x72/0xb0 > [ 6.526868] ctnetlink_dump_tuples+0x19/0x60 > [ 6.526870] ctnetlink_exp_dump_tuple+0x6f/0xd0 > [ 6.526872] ctnetlink_exp_dump_expect+0x315/0x660 > [ 6.526875] ? __pfx_ctnetlink_exp_dump_expect+0x10/0x10 > [ 6.526878] ? __kmalloc_node_track_caller_noprof+0x1c6/0x590 > [ 6.526885] ? kmalloc_reserve+0x75/0x160 > [ 6.526887] ? skb_put+0x72/0xb0 > [ 6.526889] ? __asan_memset+0x23/0x50 > [ 6.526892] ? __nlmsg_put+0x97/0xb0 > [ 6.526897] ctnetlink_exp_fill_info.constprop.0+0xf9/0x180 > [ 6.526899] ctnetlink_get_expect+0x2f3/0x400 > [ 6.526901] ? __pfx_ctnetlink_get_expect+0x10/0x10 > [ 6.526903] ? __pfx___nla_validate_parse+0x10/0x10 > [ 6.526912] ? mutex_lock+0x7e/0xd0 > [ 6.526914] ? __pfx_mutex_lock+0x10/0x10 > [ 6.526917] nfnetlink_rcv_msg+0x48e/0x510 > [ 6.526922] ? __pfx_nfnetlink_rcv_msg+0x10/0x10 > [ 6.526925] ? __sys_sendmsg+0xf4/0x180 > [ 6.526927] ? do_syscall_64+0xc3/0x6e0 > [ 6.526930] ? entry_SYSCALL_64_after_hwframe+0x76/0x7e > [ 6.526935] netlink_rcv_skb+0xc9/0x1f0 > [ 6.526937] ? __pfx_nfnetlink_rcv_msg+0x10/0x10 > [ 6.526940] ? __pfx_netlink_rcv_skb+0x10/0x10 > [ 6.526942] ? security_capable+0xda/0x160 > [ 6.526947] nfnetlink_rcv+0xdb/0x220 > [ 6.526951] ? __pfx___netlink_lookup+0x10/0x10 > [ 6.526953] ? __pfx_nfnetlink_rcv+0x10/0x10 > [ 6.526955] ? netlink_deliver_tap+0x5f/0x400 > [ 6.526958] netlink_unicast+0x3ec/0x590 > [ 6.526960] ? __pfx_netlink_unicast+0x10/0x10 > [ 6.526961] ? __pfx___alloc_skb+0x10/0x10 > [ 6.526963] ? __alloc_frozen_pages_noprof+0x26f/0x560 > [ 6.526966] ? __virt_addr_valid+0xef/0x1a0 > [ 6.526969] ? __check_object_size+0x25f/0x450 > [ 6.526973] netlink_sendmsg+0x397/0x690 > [ 6.526975] ? __pfx_netlink_sendmsg+0x10/0x10 > [ 6.526977] ? __import_iovec+0x220/0x270 > [ 6.526981] ? __check_object_size+0x4b/0x450 > [ 6.526983] ____sys_sendmsg+0x538/0x550 > [ 6.526987] ? __pfx_____sys_sendmsg+0x10/0x10 > [ 6.526990] ? __pfx_copy_msghdr_from_user+0x10/0x10 > [ 6.526992] ? __pfx_lru_add+0x10/0x10 > [ 6.526998] ___sys_sendmsg+0xfc/0x170 > [ 6.527000] ? __pfx____sys_sendmsg+0x10/0x10 > [ 6.527002] ? __pfx_do_wp_page+0x10/0x10 > [ 6.527008] __sys_sendmsg+0xf4/0x180 > [ 6.527010] ? __pfx___sys_sendmsg+0x10/0x10 > [ 6.527013] ? do_user_addr_fault+0x3b5/0x750 > [ 6.527015] do_syscall_64+0xc3/0x6e0 > [ 6.527017] entry_SYSCALL_64_after_hwframe+0x76/0x7e > [ 6.527020] RIP: 0033:0x424304 > [ 6.527025] Code: c2 c0 ff ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b5 0f 1f 00 f3 0f 1e fa 80 3d 5d 1d 09 00 00 74 13 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 4c c3 0f 1f 00 55 48 89 e5 48 83 ec 20 89 55 > [ 6.527027] RSP: 002b:00007ffcc8012368 EFLAGS: 00000202 ORIG_RAX: 000000000000002e > [ 6.527033] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000424304 > [ 6.527034] RDX: 0000000000000000 RSI: 00007ffcc80123a0 RDI: 0000000000000003 > [ 6.527035] RBP: 00007ffcc80123e0 R08: 0000000000000000 R09: 0000000000000002 > [ 6.527037] R10: 0000000020797380 R11: 0000000000000202 R12: 00007ffcc80175c8 > [ 6.527038] R13: 00007ffcc80175d8 R14: 00000000004b0828 R15: 0000000000000001 > [ 6.527040] > [ 6.527041] > [ 6.537631] Allocated by task 131: > [ 6.537736] kasan_save_stack+0x33/0x60 > [ 6.537853] kasan_save_track+0x14/0x30 > [ 6.537970] __kasan_slab_alloc+0x6e/0x70 > [ 6.538094] kmem_cache_alloc_noprof+0x134/0x440 > [ 6.538248] __nf_conntrack_alloc+0xa8/0x2b0 > [ 6.538391] ctnetlink_create_conntrack+0xa1/0x900 > [ 6.538547] ctnetlink_new_conntrack+0x3cf/0x7d0 > [ 6.538687] nfnetlink_rcv_msg+0x48e/0x510 > [ 6.538810] netlink_rcv_skb+0xc9/0x1f0 > [ 6.538926] nfnetlink_rcv+0xdb/0x220 > [ 6.539036] netlink_unicast+0x3ec/0x590 > [ 6.539155] netlink_sendmsg+0x397/0x690 > [ 6.539285] ____sys_sendmsg+0x538/0x550 > [ 6.539418] ___sys_sendmsg+0xfc/0x170 > [ 6.539545] __sys_sendmsg+0xf4/0x180 > [ 6.539658] do_syscall_64+0xc3/0x6e0 > [ 6.539769] entry_SYSCALL_64_after_hwframe+0x76/0x7e > [ 6.539916] > [ 6.539967] Freed by task 0: > [ 6.540053] kasan_save_stack+0x33/0x60 > [ 6.540165] kasan_save_track+0x14/0x30 > [ 6.540281] kasan_save_free_info+0x3b/0x60 > [ 6.540406] __kasan_slab_free+0x43/0x70 > [ 6.540523] slab_free_after_rcu_debug+0xad/0x1e0 > [ 6.540664] rcu_core+0x5c3/0x9c0 > [ 6.540769] handle_softirqs+0x148/0x460 > [ 6.540892] __irq_exit_rcu+0x97/0xf0 > [ 6.541004] sysvec_apic_timer_interrupt+0x71/0x90 > [ 6.541149] asm_sysvec_apic_timer_interrupt+0x1a/0x20 > [ 6.541304] > [ 6.541355] Last potentially related work creation: > [ 6.541498] kasan_save_stack+0x33/0x60 > [ 6.541614] kasan_record_aux_stack+0x8c/0xa0 > [ 6.541746] kmem_cache_free+0x1f5/0x440 > [ 6.541865] nf_conntrack_free+0xc1/0x140 > [ 6.541985] ctnetlink_del_conntrack+0x4c4/0x520 > [ 6.542126] nfnetlink_rcv_msg+0x48e/0x510 > [ 6.542249] netlink_rcv_skb+0xc9/0x1f0 > [ 6.542365] nfnetlink_rcv+0xdb/0x220 > [ 6.542475] netlink_unicast+0x3ec/0x590 > [ 6.542593] netlink_sendmsg+0x397/0x690 > [ 6.542711] ____sys_sendmsg+0x538/0x550 > [ 6.542830] ___sys_sendmsg+0xfc/0x170 > [ 6.542940] __sys_sendmsg+0xf4/0x180 > [ 6.543049] do_syscall_64+0xc3/0x6e0 > [ 6.543157] entry_SYSCALL_64_after_hwframe+0x76/0x7e > [ 6.543301] > [ 6.543349] The buggy address belongs to the object at ffff8881042a8c80 > [ 6.543349] which belongs to the cache nf_conntrack of size 248 > [ 6.543739] The buggy address is located 50 bytes inside of > [ 6.543739] freed 248-byte region [ffff8881042a8c80, ffff8881042a8d78) > [ 6.544101] > [ 6.544152] The buggy address belongs to the physical page: > [ 6.544316] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff8881042a8500 pfn:0x1042a8 > [ 6.544584] flags: 0x200000000000200(workingset|node=0|zone=2) > [ 6.544759] page_type: f5(slab) > [ 6.544859] raw: 0200000000000200 ffff88810485d500 ffff88810485fd10 ffff88810485fd10 > [ 6.545083] raw: ffff8881042a8500 00000008000c0004 00000000f5000000 0000000000000000 > [ 6.545308] page dumped because: kasan: bad access detected > [ 6.545469] > [ 6.545521] Memory state around the buggy address: > [ 6.545664] ffff8881042a8b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > [ 6.545878] ffff8881042a8c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > [ 6.546089] >ffff8881042a8c80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > [ 6.546300] ^ > [ 6.546442] ffff8881042a8d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc > [ 6.546654] ffff8881042a8d80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > > Fixes: c1d10adb4a52 ("[NETFILTER]: Add ctnetlink port for nf_conntrack") > Signed-off-by: Hyunwoo Kim > --- > net/netfilter/nf_conntrack_netlink.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c > index c9d725fc2d71..3225d4e98513 100644 > --- a/net/netfilter/nf_conntrack_netlink.c > +++ b/net/netfilter/nf_conntrack_netlink.c > @@ -3300,6 +3300,7 @@ static int ctnetlink_get_expect(struct sk_buff *skb, > { > u_int8_t u3 = info->nfmsg->nfgen_family; > struct nf_conntrack_tuple tuple; > + struct nf_conn *master; > struct nf_conntrack_expect *exp; > struct nf_conntrack_zone zone; > struct sk_buff *skb2; > @@ -3354,10 +3355,19 @@ static int ctnetlink_get_expect(struct sk_buff *skb, > } > > rcu_read_lock(); > + master = exp->master; > + if (!refcount_inc_not_zero(&master->ct_general.use)) { > + rcu_read_unlock(); > + nf_ct_expect_put(exp); > + kfree_skb(skb2); > + return -ENOENT; > + } > + > err = ctnetlink_exp_fill_info(skb2, NETLINK_CB(skb).portid, > info->nlh->nlmsg_seq, IPCTNL_MSG_EXP_NEW, > exp); > rcu_read_unlock(); > + nf_ct_put(master); > nf_ct_expect_put(exp); > if (err <= 0) { > kfree_skb(skb2); > -- > 2.43.0 >