rule, set_elem: fix printing of user data

Hitherto, alphanumeric characters have been printed as-is, but anything
else was replaced by '\0'.  However, this effectively truncates the
output.  Instead, print any printable character as-is and print anything
else as a hexadecimal escape sequence:

  userdata = { \x01\x04\x01\x00\x00\x00 }

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/rule.c b/src/rule.c
index 0bb1c2a..a1a64bd 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -622,8 +622,9 @@ static int nftnl_rule_snprintf_default(char *buf, size_t remain,
 		for (i = 0; i < r->user.len; i++) {
 			char *c = r->user.data;
 
-			ret = snprintf(buf + offset, remain, "%c",
-				       isalnum(c[i]) ? c[i] : 0);
+			ret = snprintf(buf + offset, remain,
+				       isprint(c[i]) ? "%c" : "\\x%02hhx",
+				       c[i]);
 			SNPRINTF_BUFFER_SIZE(ret, remain, offset);
 		}