random-util: always cast from smaller to bigger type when comparing

When we compare two size values, let's make sure we cast from the
smaller to the bigger type first, if both types differ, rather than the
reverse in order to not run into overflows.

diff --git a/src/basic/random-util.c b/src/basic/random-util.c
index 589575c..a8bcee1 100644 (file)
--- a/src/basic/random-util.c
+++ b/src/basic/random-util.c
@@ -46,8 +46,8 @@ int acquire_random_bytes(void *p, size_t n, bool high_quality_required) {
         static int have_syscall = -1;
 
         _cleanup_close_ int fd = -1;
-        int r;
         unsigned already_done = 0;
+        int r;
 
         /* Gathers some randomness from the kernel. This call will never block. If
          * high_quality_required, it will always return some data from the kernel,
@@ -61,7 +61,7 @@ int acquire_random_bytes(void *p, size_t n, bool high_quality_required) {
                 r = getrandom(p, n, GRND_NONBLOCK);
                 if (r > 0) {
                         have_syscall = true;
-                        if (r == (int) n)
+                        if ((size_t) r == n)
                                 return 0;
                         if (!high_quality_required) {
                                 /* Fill in the remaing bytes using pseudorandom values */
@@ -147,11 +147,11 @@ void pseudorandom_bytes(void *p, size_t n) {
                 rr = (unsigned) rand();
 
 #if RAND_STEP >= 3
-                if (q - (uint8_t*) p + 2 < (ptrdiff_t) n)
+                if ((size_t) (q - (uint8_t*) p + 2) < n)
                         q[2] = rr >> 16;
 #endif
 #if RAND_STEP >= 2
-                if (q - (uint8_t*) p + 1 < (ptrdiff_t) n)
+                if ((size_t) (q - (uint8_t*) p + 1) < n)
                         q[1] = rr >> 8;
 #endif
                 q[0] = rr;