netfilter: nf_conntrack_ftp: Fix debug output

BugLink: https://bugs.launchpad.net/bugs/1845405

[ Upstream commit 3a069024 ]

The find_pattern() debug output was printing the 'skip' character.
This can be a NULL-byte and messes up further pr_debug() output.

Output without the fix:
kernel: nf_conntrack_ftp: Pattern matches!
kernel: nf_conntrack_ftp: Skipped up to `<7>nf_conntrack_ftp: find_pattern `PORT': dlen = 8
kernel: nf_conntrack_ftp: find_pattern `EPRT': dlen = 8

Output with the fix:
kernel: nf_conntrack_ftp: Pattern matches!
kernel: nf_conntrack_ftp: Skipped up to 0x0 delimiter!
kernel: nf_conntrack_ftp: Match succeeded!
kernel: nf_conntrack_ftp: conntrack_ftp: match `172,17,0,100,200,207' (20 bytes at 4150681645)
kernel: nf_conntrack_ftp: find_pattern `PORT': dlen = 8
Signed-off-by: Thomas Jarosch <thomas.jarosch@intra2net.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/netfilter/nf_conntrack_ftp.c

@@ -334,7 +334,7 @@ static int find_pattern(const char *data, size_t dlen,
 		i++;
 	}
 
-	pr_debug("Skipped up to `%c'!\n", skip);
+	pr_debug("Skipped up to 0x%hhx delimiter!\n", skip);
 
 	*numoff = i;
 	*numlen = getnum(data + i, dlen - i, cmd, term, numoff);