netdev - [PATCH net 5/5] netfilter: nf_ct_ftp: fix deadlock when nat rewrite is needed

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Date:   Wed, 21 Sep 2022 09:38:25 +0200
From:   Florian Westphal <fw@...len.de>
To:     <netdev@...r.kernel.org>
Cc:     netfilter-devel@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Florian Westphal <fw@...len.de>,
        Bruno de Paula Larini <bruno.larini@...soft.com.br>
Subject: [PATCH net 5/5] netfilter: nf_ct_ftp: fix deadlock when nat rewrite is needed

We can't use ct->lock, this is already used by the seqadj internals.
When using ftp helper + nat, seqadj will attempt to acquire ct->lock
again.

Revert back to a global lock for now.

Fixes: c783a29c7e59 ("netfilter: nf_ct_ftp: prefer skb_linearize")
Reported-by: Bruno de Paula Larini <bruno.larini@...soft.com.br>
Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/netfilter/nf_conntrack_ftp.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nf_conntrack_ftp.c b/net/netfilter/nf_conntrack_ftp.c
index 0d9332e9cf71..617f744a2e3a 100644
--- a/net/netfilter/nf_conntrack_ftp.c
+++ b/net/netfilter/nf_conntrack_ftp.c
@@ -33,6 +33,7 @@ MODULE_AUTHOR("Rusty Russell <rusty@...tcorp.com.au>");
 MODULE_DESCRIPTION("ftp connection tracking helper");
 MODULE_ALIAS("ip_conntrack_ftp");
 MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
+static DEFINE_SPINLOCK(nf_ftp_lock);
 
 #define MAX_PORTS 8
 static u_int16_t ports[MAX_PORTS];
@@ -409,7 +410,8 @@ static int help(struct sk_buff *skb,
 	}
 	datalen = skb->len - dataoff;
 
-	spin_lock_bh(&ct->lock);
+	/* seqadj (nat) uses ct->lock internally, nf_nat_ftp would cause deadlock */
+	spin_lock_bh(&nf_ftp_lock);
 	fb_ptr = skb->data + dataoff;
 
 	ends_in_nl = (fb_ptr[datalen - 1] == '\n');
@@ -538,7 +540,7 @@ static int help(struct sk_buff *skb,
 	if (ends_in_nl)
 		update_nl_seq(ct, seq, ct_ftp_info, dir, skb);
  out:
-	spin_unlock_bh(&ct->lock);
+	spin_unlock_bh(&nf_ftp_lock);
 	return ret;
 }
 
-- 
2.35.1