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-rw-r--r--src/random.cpp49
1 files changed, 34 insertions, 15 deletions
diff --git a/src/random.cpp b/src/random.cpp
index 7fdada7525..8284f457c9 100644
--- a/src/random.cpp
+++ b/src/random.cpp
@@ -102,6 +102,28 @@ static void RandAddSeedPerfmon()
#endif
}
+#ifndef WIN32
+/** Fallback: get 32 bytes of system entropy from /dev/urandom. The most
+ * compatible way to get cryptographic randomness on UNIX-ish platforms.
+ */
+void GetDevURandom(unsigned char *ent32)
+{
+ int f = open("/dev/urandom", O_RDONLY);
+ if (f == -1) {
+ RandFailure();
+ }
+ int have = 0;
+ do {
+ ssize_t n = read(f, ent32 + have, NUM_OS_RANDOM_BYTES - have);
+ if (n <= 0 || n + have > NUM_OS_RANDOM_BYTES) {
+ RandFailure();
+ }
+ have += n;
+ } while (have < NUM_OS_RANDOM_BYTES);
+ close(f);
+}
+#endif
+
/** Get 32 bytes of system entropy. */
void GetOSRand(unsigned char *ent32)
{
@@ -122,8 +144,17 @@ void GetOSRand(unsigned char *ent32)
* will always return as many bytes as requested and will not be
* interrupted by signals."
*/
- if (syscall(SYS_getrandom, ent32, NUM_OS_RANDOM_BYTES, 0) != NUM_OS_RANDOM_BYTES) {
- RandFailure();
+ int rv = syscall(SYS_getrandom, ent32, NUM_OS_RANDOM_BYTES, 0);
+ if (rv != NUM_OS_RANDOM_BYTES) {
+ if (rv < 0 && errno == ENOSYS) {
+ /* Fallback for kernel <3.17: the return value will be -1 and errno
+ * ENOSYS if the syscall is not available, in that case fall back
+ * to /dev/urandom.
+ */
+ GetDevURandom(ent32);
+ } else {
+ RandFailure();
+ }
}
#elif defined(HAVE_GETENTROPY)
/* On OpenBSD this can return up to 256 bytes of entropy, will return an
@@ -150,19 +181,7 @@ void GetOSRand(unsigned char *ent32)
/* Fall back to /dev/urandom if there is no specific method implemented to
* get system entropy for this OS.
*/
- int f = open("/dev/urandom", O_RDONLY);
- if (f == -1) {
- RandFailure();
- }
- int have = 0;
- do {
- ssize_t n = read(f, ent32 + have, NUM_OS_RANDOM_BYTES - have);
- if (n <= 0 || n + have > NUM_OS_RANDOM_BYTES) {
- RandFailure();
- }
- have += n;
- } while (have < NUM_OS_RANDOM_BYTES);
- close(f);
+ GetDevURandom(ent32);
#endif
}