Merge branch 'ps/reftable-get-random-fix' into next

The code to compute "unique" name used git_rand() which can fail or
get stuck; the callsite does not require cryptographic security.
Introduce the "insecure" mode and use it appropriately.

* ps/reftable-get-random-fix:
  reftable/stack: accept insecure random bytes
  wrapper: allow generating insecure random bytes

builtin/gc.c

@@ -1909,7 +1909,7 @@ static int get_random_minute(void)
 	if (getenv("GIT_TEST_MAINT_SCHEDULER"))
 		return 13;
 
-	return git_rand() % 60;
+	return git_rand(0) % 60;
 }
 
 static int is_launchctl_available(void)

reftable/stack.c

@@ -493,7 +493,7 @@ static int reftable_stack_reload_maybe_reuse(struct reftable_stack *st,
 		close(fd);
 		fd = -1;
 
-		delay = delay + (delay * rand()) / RAND_MAX + 1;
+		delay = delay + (delay * git_rand(CSPRNG_BYTES_INSECURE)) / UINT32_MAX + 1;
 		sleep_millisec(delay);
 	}
 
@@ -659,7 +659,7 @@ int reftable_stack_add(struct reftable_stack *st,
 static int format_name(struct reftable_buf *dest, uint64_t min, uint64_t max)
 {
 	char buf[100];
-	uint32_t rnd = (uint32_t)git_rand();
+	uint32_t rnd = git_rand(CSPRNG_BYTES_INSECURE);
 	snprintf(buf, sizeof(buf), "0x%012" PRIx64 "-0x%012" PRIx64 "-%08x",
 		 min, max, rnd);
 	reftable_buf_reset(dest);

t/helper/test-csprng.c

@@ -15,7 +15,7 @@ int cmd__csprng(int argc, const char **argv)
 
 	while (count) {
 		unsigned long chunk = count < sizeof(buf) ? count : sizeof(buf);
-		if (csprng_bytes(buf, chunk) < 0) {
+		if (csprng_bytes(buf, chunk, 0) < 0) {
 			perror("failed to read");
 			return 5;
 		}

t/unit-tests/t-reftable-readwrite.c

@@ -108,8 +108,8 @@ static void t_log_buffer_size(void)
 	   hash, to ensure that the compressed part is larger than the original.
 	*/
 	for (i = 0; i < REFTABLE_HASH_SIZE_SHA1; i++) {
-		log.value.update.old_hash[i] = (uint8_t)(git_rand() % 256);
-		log.value.update.new_hash[i] = (uint8_t)(git_rand() % 256);
+		log.value.update.old_hash[i] = (uint8_t)(git_rand(0) % 256);
+		log.value.update.new_hash[i] = (uint8_t)(git_rand(0) % 256);
 	}
 	reftable_writer_set_limits(w, update_index, update_index);
 	err = reftable_writer_add_log(w, &log);
@@ -325,7 +325,7 @@ static void t_log_zlib_corruption(void)
 	};
 
 	for (i = 0; i < sizeof(message) - 1; i++)
-		message[i] = (uint8_t)(git_rand() % 64 + ' ');
+		message[i] = (uint8_t)(git_rand(0) % 64 + ' ');
 
 	reftable_writer_set_limits(w, 1, 1);
 

wrapper.c

@@ -479,7 +479,7 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
 	for (count = 0; count < TMP_MAX; ++count) {
 		int i;
 		uint64_t v;
-		if (csprng_bytes(&v, sizeof(v)) < 0)
+		if (csprng_bytes(&v, sizeof(v), 0) < 0)
 			return error_errno("unable to get random bytes for temporary file");
 
 		/* Fill in the random bits. */
@@ -750,7 +750,7 @@ int open_nofollow(const char *path, int flags)
 #endif
 }
 
-int csprng_bytes(void *buf, size_t len)
+int csprng_bytes(void *buf, size_t len, MAYBE_UNUSED unsigned flags)
 {
 #if defined(HAVE_ARC4RANDOM) || defined(HAVE_ARC4RANDOM_LIBBSD)
 	/* This function never returns an error. */
@@ -785,14 +785,18 @@ int csprng_bytes(void *buf, size_t len)
 		return -1;
 	return 0;
 #elif defined(HAVE_OPENSSL_CSPRNG)
-	int res = RAND_bytes(buf, len);
-	if (res == 1)
+	switch (RAND_pseudo_bytes(buf, len)) {
+	case 1:
 		return 0;
-	if (res == -1)
-		errno = ENOTSUP;
-	else
+	case 0:
+		if (flags & CSPRNG_BYTES_INSECURE)
+			return 0;
 		errno = EIO;
-	return -1;
+		return -1;
+	default:
+		errno = ENOTSUP;
+		return -1;
+	}
 #else
 	ssize_t res;
 	char *p = buf;
@@ -816,11 +820,11 @@ int csprng_bytes(void *buf, size_t len)
 #endif
 }
 
-uint32_t git_rand(void)
+uint32_t git_rand(unsigned flags)
 {
 	uint32_t result;
 
-	if (csprng_bytes(&result, sizeof(result)) < 0)
+	if (csprng_bytes(&result, sizeof(result), flags) < 0)
 		die(_("unable to get random bytes"));
 
 	return result;

wrapper.h

@@ -127,18 +127,26 @@ int open_nofollow(const char *path, int flags);
 
 void sleep_millisec(int millisec);
 
+enum {
+	/*
+	 * Accept insecure bytes, which some CSPRNG implementations may return
+	 * in case the entropy pool has been exhausted.
+	 */
+	CSPRNG_BYTES_INSECURE = (1 << 0),
+};
+
 /*
  * Generate len bytes from the system cryptographically secure PRNG.
  * Returns 0 on success and -1 on error, setting errno.  The inability to
- * satisfy the full request is an error.
+ * satisfy the full request is an error. Accepts CSPRNG flags.
  */
-int csprng_bytes(void *buf, size_t len);
+int csprng_bytes(void *buf, size_t len, unsigned flags);
 
 /*
  * Returns a random uint32_t, uniformly distributed across all possible
- * values.
+ * values. Accepts CSPRNG flags.
  */
-uint32_t git_rand(void);
+uint32_t git_rand(unsigned flags);
 
 /* Provide log2 of the given `size_t`. */
 static inline unsigned log2u(uintmax_t sz)