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Message-Id: <20241002202421.1281311-4-pablo@netfilter.org>
Date: Wed, 2 Oct 2024 22:24:20 +0200
From: Pablo Neira Ayuso <pablo@...filter.org>
To: netfilter-devel@...r.kernel.org
Cc: davem@...emloft.net,
netdev@...r.kernel.org,
kuba@...nel.org,
pabeni@...hat.com,
edumazet@...gle.com,
fw@...len.de
Subject: [PATCH net 3/4] netfilter: nf_tables: prevent nf_skb_duplicated corruption
From: Eric Dumazet <edumazet@...gle.com>
syzbot found that nf_dup_ipv4() or nf_dup_ipv6() could write
per-cpu variable nf_skb_duplicated in an unsafe way [1].
Disabling preemption as hinted by the splat is not enough,
we have to disable soft interrupts as well.
[1]
BUG: using __this_cpu_write() in preemptible [00000000] code: syz.4.282/6316
caller is nf_dup_ipv4+0x651/0x8f0 net/ipv4/netfilter/nf_dup_ipv4.c:87
CPU: 0 UID: 0 PID: 6316 Comm: syz.4.282 Not tainted 6.11.0-rc7-syzkaller-00104-g7052622fccb1 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:93 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:119
check_preemption_disabled+0x10e/0x120 lib/smp_processor_id.c:49
nf_dup_ipv4+0x651/0x8f0 net/ipv4/netfilter/nf_dup_ipv4.c:87
nft_dup_ipv4_eval+0x1db/0x300 net/ipv4/netfilter/nft_dup_ipv4.c:30
expr_call_ops_eval net/netfilter/nf_tables_core.c:240 [inline]
nft_do_chain+0x4ad/0x1da0 net/netfilter/nf_tables_core.c:288
nft_do_chain_ipv4+0x202/0x320 net/netfilter/nft_chain_filter.c:23
nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
nf_hook_slow+0xc3/0x220 net/netfilter/core.c:626
nf_hook+0x2c4/0x450 include/linux/netfilter.h:269
NF_HOOK_COND include/linux/netfilter.h:302 [inline]
ip_output+0x185/0x230 net/ipv4/ip_output.c:433
ip_local_out net/ipv4/ip_output.c:129 [inline]
ip_send_skb+0x74/0x100 net/ipv4/ip_output.c:1495
udp_send_skb+0xacf/0x1650 net/ipv4/udp.c:981
udp_sendmsg+0x1c21/0x2a60 net/ipv4/udp.c:1269
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0x1a6/0x270 net/socket.c:745
____sys_sendmsg+0x525/0x7d0 net/socket.c:2597
___sys_sendmsg net/socket.c:2651 [inline]
__sys_sendmmsg+0x3b2/0x740 net/socket.c:2737
__do_sys_sendmmsg net/socket.c:2766 [inline]
__se_sys_sendmmsg net/socket.c:2763 [inline]
__x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2763
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4ce4f7def9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f4ce5d4a038 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f4ce5135f80 RCX: 00007f4ce4f7def9
RDX: 0000000000000001 RSI: 0000000020005d40 RDI: 0000000000000006
RBP: 00007f4ce4ff0b76 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f4ce5135f80 R15: 00007ffd4cbc6d68
</TASK>
Fixes: d877f07112f1 ("netfilter: nf_tables: add nft_dup expression")
Reported-by: syzbot <syzkaller@...glegroups.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
net/ipv4/netfilter/nf_dup_ipv4.c | 7 +++++--
net/ipv6/netfilter/nf_dup_ipv6.c | 7 +++++--
2 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/net/ipv4/netfilter/nf_dup_ipv4.c b/net/ipv4/netfilter/nf_dup_ipv4.c
index f4aed0789d69..ec94ee1051c7 100644
--- a/net/ipv4/netfilter/nf_dup_ipv4.c
+++ b/net/ipv4/netfilter/nf_dup_ipv4.c
@@ -53,8 +53,9 @@ void nf_dup_ipv4(struct net *net, struct sk_buff *skb, unsigned int hooknum,
{
struct iphdr *iph;
+ local_bh_disable();
if (this_cpu_read(nf_skb_duplicated))
- return;
+ goto out;
/*
* Copy the skb, and route the copy. Will later return %XT_CONTINUE for
* the original skb, which should continue on its way as if nothing has
@@ -62,7 +63,7 @@ void nf_dup_ipv4(struct net *net, struct sk_buff *skb, unsigned int hooknum,
*/
skb = pskb_copy(skb, GFP_ATOMIC);
if (skb == NULL)
- return;
+ goto out;
#if IS_ENABLED(CONFIG_NF_CONNTRACK)
/* Avoid counting cloned packets towards the original connection. */
@@ -91,6 +92,8 @@ void nf_dup_ipv4(struct net *net, struct sk_buff *skb, unsigned int hooknum,
} else {
kfree_skb(skb);
}
+out:
+ local_bh_enable();
}
EXPORT_SYMBOL_GPL(nf_dup_ipv4);
diff --git a/net/ipv6/netfilter/nf_dup_ipv6.c b/net/ipv6/netfilter/nf_dup_ipv6.c
index a0a2de30be3e..0c39c77fe8a8 100644
--- a/net/ipv6/netfilter/nf_dup_ipv6.c
+++ b/net/ipv6/netfilter/nf_dup_ipv6.c
@@ -47,11 +47,12 @@ static bool nf_dup_ipv6_route(struct net *net, struct sk_buff *skb,
void nf_dup_ipv6(struct net *net, struct sk_buff *skb, unsigned int hooknum,
const struct in6_addr *gw, int oif)
{
+ local_bh_disable();
if (this_cpu_read(nf_skb_duplicated))
- return;
+ goto out;
skb = pskb_copy(skb, GFP_ATOMIC);
if (skb == NULL)
- return;
+ goto out;
#if IS_ENABLED(CONFIG_NF_CONNTRACK)
nf_reset_ct(skb);
@@ -69,6 +70,8 @@ void nf_dup_ipv6(struct net *net, struct sk_buff *skb, unsigned int hooknum,
} else {
kfree_skb(skb);
}
+out:
+ local_bh_enable();
}
EXPORT_SYMBOL_GPL(nf_dup_ipv6);
--
2.30.2
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