netfilter: nf_ct_ftp: fix deadlock when nat rewrite is needed

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2139501

commit d250889
Author: Florian Westphal <fw@strlen.de>
Date:   Tue Sep 20 18:31:30 2022 +0200

    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: c783a29 ("netfilter: nf_ct_ftp: prefer skb_linearize")
    Reported-by: Bruno de Paula Larini <bruno.larini@riosoft.com.br>
    Signed-off-by: Florian Westphal <fw@strlen.de>

Signed-off-by: Ivan Vecera <ivecera@redhat.com>

Author: ivecera

net/netfilter/nf_conntrack_ftp.c

@@ -33,6 +33,7 @@ MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.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;
 }