Fix format-truncation compile failure by typecasting USB IDs (#8250)

This patch adds safe_atoux16 for parsing an unsigned hexadecimal 16bit int, and
uses that for parsing USB device and vendor IDs.

This fixes a compile error with gcc-8 because while we know that USB IDs are 2 bytes,
the compiler does not know that.

../src/udev/udev-builtin-hwdb.c:80:38: error: '%04X' directive output may be
truncated writing between 4 and 8 bytes into a region of size between 2 and 6
[-Werror=format-truncation=]

Signed-off-by: Adam Williamson <awilliam@redhat.com>
Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>

src/basic/parse-util.c

@@ -531,6 +531,30 @@ int safe_atoi16(const char *s, int16_t *ret) {
         return 0;
 }
 
+int safe_atoux16(const char *s, uint16_t *ret) {
+        char *x = NULL;
+        unsigned long l;
+
+        assert(s);
+        assert(ret);
+
+        s += strspn(s, WHITESPACE);
+
+        errno = 0;
+        l = strtoul(s, &x, 16);
+        if (errno > 0)
+                return -errno;
+        if (!x || x == s || *x != 0)
+                return -EINVAL;
+        if (s[0] == '-')
+                return -ERANGE;
+        if ((unsigned long) (uint16_t) l != l)
+                return -ERANGE;
+
+        *ret = (uint16_t) l;
+        return 0;
+}
+
 int safe_atod(const char *s, double *ret_d) {
         _cleanup_(freelocalep) locale_t loc = (locale_t) 0;
         char *x = NULL;

src/basic/parse-util.h

@@ -54,6 +54,8 @@ int safe_atou8(const char *s, uint8_t *ret);
 int safe_atou16(const char *s, uint16_t *ret);
 int safe_atoi16(const char *s, int16_t *ret);
 
+int safe_atoux16(const char *s, uint16_t *ret);
+
 static inline int safe_atou32(const char *s, uint32_t *ret_u) {
         assert_cc(sizeof(uint32_t) == sizeof(unsigned));
         return safe_atou(s, (unsigned*) ret_u);

src/test/test-parse-util.c

@@ -468,6 +468,44 @@ static void test_safe_atoi16(void) {
         assert_se(r == -EINVAL);
 }
 
+static void test_safe_atoux16(void) {
+        int r;
+        uint16_t l;
+
+        r = safe_atoux16("1234", &l);
+        assert_se(r == 0);
+        assert_se(l == 0x1234);
+
+        r = safe_atoux16("abcd", &l);
+        assert_se(r == 0);
+        assert_se(l == 0xabcd);
+
+        r = safe_atoux16("  1234", &l);
+        assert_se(r == 0);
+        assert_se(l == 0x1234);
+
+        r = safe_atoux16("12345", &l);
+        assert_se(r == -ERANGE);
+
+        r = safe_atoux16("-1", &l);
+        assert_se(r == -ERANGE);
+
+        r = safe_atoux16("  -1", &l);
+        assert_se(r == -ERANGE);
+
+        r = safe_atoux16("junk", &l);
+        assert_se(r == -EINVAL);
+
+        r = safe_atoux16("123x", &l);
+        assert_se(r == -EINVAL);
+
+        r = safe_atoux16("12.3", &l);
+        assert_se(r == -EINVAL);
+
+        r = safe_atoux16("", &l);
+        assert_se(r == -EINVAL);
+}
+
 static void test_safe_atou64(void) {
         int r;
         uint64_t l;
@@ -745,6 +783,7 @@ int main(int argc, char *argv[]) {
         test_safe_atolli();
         test_safe_atou16();
         test_safe_atoi16();
+        test_safe_atoux16();
         test_safe_atou64();
         test_safe_atoi64();
         test_safe_atod();

src/udev/udev-builtin-hwdb.c

@@ -27,6 +27,7 @@
 
 #include "alloc-util.h"
 #include "hwdb-util.h"
+#include "parse-util.h"
 #include "string-util.h"
 #include "udev-util.h"
 #include "udev.h"
@@ -63,20 +64,18 @@ int udev_builtin_hwdb_lookup(struct udev_device *dev,
 
 static const char *modalias_usb(struct udev_device *dev, char *s, size_t size) {
         const char *v, *p;
-        int vn, pn;
+        uint16_t vn, pn;
 
         v = udev_device_get_sysattr_value(dev, "idVendor");
         if (!v)
                 return NULL;
         p = udev_device_get_sysattr_value(dev, "idProduct");
         if (!p)
                 return NULL;
-        vn = strtol(v, NULL, 16);
-        if (vn <= 0)
-                return NULL;
-        pn = strtol(p, NULL, 16);
-        if (pn <= 0)
-                return NULL;
+        if (safe_atoux16(v, &vn) < 0)
+		return NULL;
+        if (safe_atoux16(p, &pn) < 0)
+		return NULL;
         snprintf(s, size, "usb:v%04Xp%04X*", vn, pn);
         return s;
 }