[PATCH libnftnl] rule, set_elem: fix printing of user data

[PATCH libnftnl] rule, set_elem: fix printing of user data

[Jeremy Sowden]

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>
---
 src/rule.c     | 5 +++--
 src/set_elem.c | 7 ++++---
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/rule.c b/src/rule.c
index 0bb1c2a0583c..a1a64bd2837d 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);
 		}
 
diff --git a/src/set_elem.c b/src/set_elem.c
index 95009acb17dc..1c8720dc7c57 100644
--- a/src/set_elem.c
+++ b/src/set_elem.c
@@ -735,14 +735,15 @@ int nftnl_set_elem_snprintf_default(char *buf, size_t remain,
 	SNPRINTF_BUFFER_SIZE(ret, remain, offset);
 
 	if (e->user.len) {
-		ret = snprintf(buf + offset, remain, "  userdata = {");
+		ret = snprintf(buf + offset, remain, "  userdata = { ");
 		SNPRINTF_BUFFER_SIZE(ret, remain, offset);
 
 		for (i = 0; i < e->user.len; i++) {
 			char *c = e->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);
 		}
 
-- 
2.35.1

Re: [PATCH libnftnl] rule, set_elem: fix printing of user data

[Pablo Neira Ayuso]

On Sat, Aug 27, 2022 at 06:17:17PM +0100, Jeremy Sowden wrote:
> 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 }

Applied, thanks