uclient: cast to unsigned char before ctype classifications

C specifies that the ctype functions (isspace, isalpha, isxdigit,
tolower, ...) have defined behaviour only for values that are
representable as unsigned char or equal to EOF. Passing a plain char
with a negative value is undefined behaviour and can trigger asan
reports or wrong results depending on the libc implementation.

Cast the argument to unsigned char at every call site.

Assisted-by: Claude:claude-opus-4-7
Link: https://github.com/openwrt/uclient/pull/16
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

3 files changed, 8 insertions, 8 deletions

diff --git a/uclient-fetch.c b/uclient-fetch.c
index 2afa3fd..3a6389d 100644
--- a/uclient-fetch.c
+++ b/uclient-fetch.c
@@ -591,12 +591,12 @@ static bool is_valid_header(char *str)
 	char *tmp = str;
 
 	/* First character must be a letter */
-	if (!isalpha(*tmp))
+	if (!isalpha((unsigned char)*tmp))
 		return false;
 
 	/* Subsequent characters must be letters, numbers or dashes */
 	while (*(++tmp) != '\0') {
-		if (!isalnum(*tmp) && *tmp != '-')
+		if (!isalnum((unsigned char)*tmp) && *tmp != '-')
 			return false;
 	}
 
@@ -771,7 +771,7 @@ int main(int argc, char **argv)
 					goto out;
 				}
 				*(tmp++) = '\0';
-				while (isspace(*tmp))
+				while (isspace((unsigned char)*tmp))
 					++tmp;
 
 				if (*tmp == '\0' || !is_valid_header(optarg) || strchr(tmp, '\n')) {
diff --git a/uclient-http.c b/uclient-http.c
index 6663628..7b25e89 100644
--- a/uclient-http.c
+++ b/uclient-http.c
@@ -531,7 +531,7 @@ uclient_http_add_auth_digest(struct uclient_http *uh)
 		const char **dest = NULL;
 		const char *tmp;
 
-		while (*next && isspace(*next))
+		while (*next && isspace((unsigned char)*next))
 			next++;
 
 		if (strmatch(&next, "realm"))
@@ -765,10 +765,10 @@ static void uclient_parse_http_line(struct uclient_http *uh, char *data)
 	*(sep++) = 0;
 
 	for (name = data; *name; name++)
-		*name = tolower(*name);
+		*name = tolower((unsigned char)*name);
 
 	name = data;
-	while (isspace(*sep))
+	while (isspace((unsigned char)*sep))
 		sep++;
 
 	blobmsg_add_string(&uh->meta, name, sep);
@@ -815,7 +815,7 @@ static void __uclient_notify_read(struct uclient_http *uh)
 				if (!*next)
 					return;
 
-				if (isspace(*next) && *next != '\r' && *next != '\n') {
+				if (isspace((unsigned char)*next) && *next != '\r' && *next != '\n') {
 					sep[0] = ' ';
 					if (sep + 1 < next)
 						sep[1] = ' ';
diff --git a/uclient-utils.c b/uclient-utils.c
index 3eaf2d5..71c30e2 100644
--- a/uclient-utils.c
+++ b/uclient-utils.c
@@ -78,7 +78,7 @@ int uclient_urldecode(const char *in, char *out, bool decode_plus)
 
 	while ((c = *(in++))) {
 		if (c == '%') {
-			if (!isxdigit(in[0]) || !isxdigit(in[1]))
+			if (!isxdigit((unsigned char)in[0]) || !isxdigit((unsigned char)in[1]))
 				return -1;
 
 			dec[0] = in[0];