netdev - [PATCH nf] netfilter: tproxy: bail out if IP has been disabled on the device

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Message-ID: <20240513102751.16105-1-fw@strlen.de>
Date: Mon, 13 May 2024 12:27:15 +0200
From: Florian Westphal <fw@...len.de>
To: <netfilter-devel@...r.kernel.org>
Cc: netdev@...r.kernel.org,
	syzkaller-bugs@...glegroups.com,
	Florian Westphal <fw@...len.de>,
	syzbot+b94a6818504ea90d7661@...kaller.appspotmail.com
Subject: [PATCH nf] netfilter: tproxy: bail out if IP has been disabled on the device

syzbot reports:
general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
[..]
RIP: 0010:nf_tproxy_laddr4+0xb7/0x340 net/ipv4/netfilter/nf_tproxy_ipv4.c:62
Call Trace:
 nft_tproxy_eval_v4 net/netfilter/nft_tproxy.c:56 [inline]
 nft_tproxy_eval+0xa9a/0x1a00 net/netfilter/nft_tproxy.c:168

__in_dev_get_rcu() can return NULL, so check for this.

Reported-and-tested-by: syzbot+b94a6818504ea90d7661@...kaller.appspotmail.com
Fixes: cc6eb4338569 ("tproxy: use the interface primary IP address as a default value for --on-ip")
Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/ipv4/netfilter/nf_tproxy_ipv4.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/netfilter/nf_tproxy_ipv4.c b/net/ipv4/netfilter/nf_tproxy_ipv4.c
index 69e331799604..73e66a088e25 100644
--- a/net/ipv4/netfilter/nf_tproxy_ipv4.c
+++ b/net/ipv4/netfilter/nf_tproxy_ipv4.c
@@ -58,6 +58,8 @@ __be32 nf_tproxy_laddr4(struct sk_buff *skb, __be32 user_laddr, __be32 daddr)
 
 	laddr = 0;
 	indev = __in_dev_get_rcu(skb->dev);
+	if (!indev)
+		return daddr;
 
 	in_dev_for_each_ifa_rcu(ifa, indev) {
 		if (ifa->ifa_flags & IFA_F_SECONDARY)
-- 
2.43.2