#include "random-util.h"
#include "time-util.h"
-int dev_urandom(void *p, size_t n) {
+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;
- /* Gathers some randomness from the kernel. This call will
- * never block, and will always return some data from the
- * kernel, regardless if the random pool is fully initialized
- * or not. It thus makes no guarantee for the quality of the
- * returned entropy, but is good enough for our usual usecases
- * of seeding the hash functions for hashtable */
+ /* Gathers some randomness from the kernel. This call will never block. If
+ * high_quality_required, it will always return some data from the kernel,
+ * regardless of whether the random pool is fully initialized or not.
+ * Otherwise, it will return success if at least some random bytes were
+ * successfully acquired, and an error if the kernel has no entropy whatsover
+ * for us. */
- /* Use the getrandom() syscall unless we know we don't have
- * it, or when the requested size is too large for it. */
- if (have_syscall != 0 || (size_t) (int) n != n) {
+ /* Use the getrandom() syscall unless we know we don't have it. */
+ if (have_syscall != 0) {
r = getrandom(p, n, GRND_NONBLOCK);
- if (r == (int) n) {
+ if (r > 0) {
have_syscall = true;
- return 0;
- }
-
- if (r < 0) {
- if (errno == ENOSYS)
- /* we lack the syscall, continue with
- * reading from /dev/urandom */
- have_syscall = false;
- else if (errno == EAGAIN)
- /* not enough entropy for now. Let's
- * remember to use the syscall the
- * next time, again, but also read
- * from /dev/urandom for now, which
- * doesn't care about the current
- * amount of entropy. */
- have_syscall = true;
- else
- return -errno;
+ if (r == n)
+ return 0;
+ if (!high_quality_required) {
+ /* Fill in the remaing bytes using pseudorandom values */
+ pseudorandom_bytes((uint8_t*) p + r, n - r);
+ return 0;
+ }
+
+ already_done = r;
+ } else if (errno == ENOSYS)
+ /* We lack the syscall, continue with reading from /dev/urandom. */
+ have_syscall = false;
+ else if (errno == EAGAIN) {
+ /* The kernel has no entropy whatsoever. Let's remember to
+ * use the syscall the next time again though.
+ *
+ * If high_quality_required is false, return an error so that
+ * random_bytes() can produce some pseudorandom
+ * bytes. Otherwise, fall back to /dev/urandom, which we know
+ * is empty, but the kernel will produce some bytes for us on
+ * a best-effort basis. */
+ have_syscall = true;
+
+ if (!high_quality_required)
+ return -ENODATA;
} else
- /* too short read? */
- return -ENODATA;
+ return -errno;
}
fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
if (fd < 0)
return errno == ENOENT ? -ENOSYS : -errno;
- return loop_read_exact(fd, p, n, true);
+ return loop_read_exact(fd, (uint8_t*) p + already_done, n - already_done, true);
}
void initialize_srand(void) {
return;
#ifdef HAVE_SYS_AUXV_H
- /* The kernel provides us with 16 bytes of entropy in auxv, so let's try to make use of that to seed the
- * pseudo-random generator. It's better than nothing... */
+ /* The kernel provides us with 16 bytes of entropy in auxv, so let's
+ * try to make use of that to seed the pseudo-random generator. It's
+ * better than nothing... */
auxv = (void*) getauxval(AT_RANDOM);
if (auxv) {
srand_called = true;
}
-void random_bytes(void *p, size_t n) {
+/* INT_MAX gives us only 31 bits, so use 24 out of that. */
+#if RAND_MAX >= INT_MAX
+# define RAND_STEP 3
+#else
+/* SHORT_INT_MAX or lower gives at most 15 bits, we just just 8 out of that. */
+# define RAND_STEP 1
+#endif
+
+void pseudorandom_bytes(void *p, size_t n) {
uint8_t *q;
+
+ initialize_srand();
+
+ for (q = p; q < (uint8_t*) p + n; q += RAND_STEP) {
+ unsigned rr;
+
+ rr = (unsigned) rand();
+
+#if RAND_STEP >= 3
+ if (q - (uint8_t*) p + 2 < n)
+ q[2] = rr >> 16;
+#endif
+#if RAND_STEP >= 2
+ if (q - (uint8_t*) p + 1 < n)
+ q[1] = rr >> 8;
+#endif
+ q[0] = rr;
+ }
+}
+
+void random_bytes(void *p, size_t n) {
int r;
- r = dev_urandom(p, n);
+ r = acquire_random_bytes(p, n, false);
if (r >= 0)
return;
- /* If some idiot made /dev/urandom unavailable to us, he'll
- * get a PRNG instead. */
-
- initialize_srand();
-
- for (q = p; q < (uint8_t*) p + n; q ++)
- *q = rand();
+ /* If some idiot made /dev/urandom unavailable to us, or the
+ * kernel has no entropy, use a PRNG instead. */
+ return pseudorandom_bytes(p, n);
}
~ianmdlvl / elogind.git / blobdiff