[klibc] inet: Stricter byte parsing in inet_aton()

sscanf() skips spaces in some places, and accepts values that are
out-of-range for a byte, so the following strings are wrongly
accepted:

"1.2.3.256"
"256.1.2.3"
"-1.2.3.4"
"1.2.3.-4"
" 1.2.3.4"
"1. 2.3.4"
"1.2.3.4 "
"1.2.3.0x4"

Implement our own strict conversion of decimal digits to bytes.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

1 files changed, 24 insertions, 6 deletions

diff --git a/usr/klibc/inet/inet_aton.c b/usr/klibc/inet/inet_aton.c
index beceeea36a733..954e5d8d90be6 100644
--- a/usr/klibc/inet/inet_aton.c
+++ b/usr/klibc/inet/inet_aton.c
@@ -3,20 +3,38 @@
  */
 
 #include <arpa/inet.h>
+#include <ctype.h>
 #include <stdio.h>
 
 int inet_aton(const char *str, struct in_addr *addr)
 {
+	int i = 0, digits = 0, val = 0;
 	union {
 		uint8_t	 b[4];
 		uint32_t l;
 	} a;
+	char ch;
 
-	if (sscanf(str, "%hhu.%hhu.%hhu.%hhu",
-		   &a.b[0], &a.b[1], &a.b[2], &a.b[3]) == 4) {
-		addr->s_addr = a.l;	/* Always in network byte order */
-		return 1;
-	} else {
-		return 0;
+	for (;;) {
+		ch = *str++;
+		if (ch == (i == 3 ? 0 : '.')) {
+			if (digits == 0)
+				return 0;
+			a.b[i] = val;
+			if (++i == 4)
+				break;
+			digits = 0;
+			val = 0;
+		} else if (isdigit((unsigned char)ch)) {
+			digits++;
+			val = val * 10 + (ch - '0');
+			if (val > 0xff)
+				return 0;
+		} else {
+			return 0;
+		}
 	}
+
+	addr->s_addr = a.l;
+	return 1;
 }