From: Sami Kerola Date: Sun, 11 Dec 2016 11:43:37 +0000 (+0000) Subject: lib/randutils: use getrandom(2) when it is available X-Git-Tag: v2.30-rc1~331^2 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=cc01c2dca4f62e36505570d5cb15f868aa44bf54;p=thirdparty%2Futil-linux.git lib/randutils: use getrandom(2) when it is available System call getrandom(2) is relatively new, available since kernel 3.17 but not supported by glibc 2.24. That in mind autotools is made to check availability of this function and keep old code as fallback. It is reasonable assume it will take years before the syscall(2) and fallback are unproblematic to remove. One might ask why bother using getrandom(2). Main reason is to avoid unnecessary system calls to achieve exactly same end result. That demonstrated with 'strace -c ./mcookie' showing 36 calls before, and 32 after this change. Secondly the getrandom(2) function got to kernel with promise it can be used to avoid file descriptor run down, and since uuidd uses random_get_bytes() it should fulfill it's promise here. Reference: http://man7.org/linux/man-pages/man2/getrandom.2.html Reference: https://lwn.net/Articles/606141/ Reviewed-by: Karel Zak Signed-off-by: Sami Kerola --- diff --git a/configure.ac b/configure.ac index e0240b322e..d301b3da2f 100644 --- a/configure.ac +++ b/configure.ac @@ -385,6 +385,7 @@ AC_CHECK_FUNCS([ \ getdtablesize \ getexecname \ getmntinfo \ + getrandom \ getrlimit \ getsgnam \ inotify_init \ diff --git a/lib/randutils.c b/lib/randutils.c index b93b9ba470..8defe744c6 100644 --- a/lib/randutils.c +++ b/lib/randutils.c @@ -25,6 +25,25 @@ #define THREAD_LOCAL static #endif +#ifdef HAVE_GETRANDOM +# include +#elif defined (__linux__) +# include +# if !defined(SYS_getrandom) && defined(__NR_getrandom) + /* usable kernel-headers, but old glibc-headers */ +# define SYS_getrandom __NR_getrandom +# endif +#endif + +#if !defined(HAVE_GETRANDOM) && defined(SYS_getrandom) +/* libc without function, but we have syscal */ +static int getrandom(void *buf, size_t buflen, unsigned int flags) +{ + return (syscall(SYS_getrandom, buf, buflen, flags)); +} +# define HAVE_GETRANDOM +#endif + #if defined(__linux__) && defined(__NR_gettid) && defined(HAVE_JRAND48) #define DO_JRAND_MIX THREAD_LOCAL unsigned short ul_jrand_seed[3]; @@ -35,20 +54,11 @@ int rand_get_number(int low_n, int high_n) return rand() % (high_n - low_n + 1) + low_n; } -int random_get_fd(void) +static void crank_random(void) { - int i, fd; + int i; struct timeval tv; - fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC); - if (fd == -1) - fd = open("/dev/random", O_RDONLY | O_NONBLOCK | O_CLOEXEC); - if (fd >= 0) { - i = fcntl(fd, F_GETFD); - if (i >= 0) - fcntl(fd, F_SETFD, i | FD_CLOEXEC); - } - gettimeofday(&tv, 0); srand((getpid() << 16) ^ getuid() ^ tv.tv_sec ^ tv.tv_usec); @@ -61,9 +71,23 @@ int random_get_fd(void) gettimeofday(&tv, 0); for (i = (tv.tv_sec ^ tv.tv_usec) & 0x1F; i > 0; i--) rand(); - return fd; } +int random_get_fd(void) +{ + int i, fd; + + fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC); + if (fd == -1) + fd = open("/dev/random", O_RDONLY | O_NONBLOCK | O_CLOEXEC); + if (fd >= 0) { + i = fcntl(fd, F_GETFD); + if (i >= 0) + fcntl(fd, F_SETFD, i | FD_CLOEXEC); + } + crank_random(); + return fd; +} /* * Generate a stream of random nbytes into buf. @@ -72,10 +96,19 @@ int random_get_fd(void) */ void random_get_bytes(void *buf, size_t nbytes) { - size_t i, n = nbytes; + size_t i; + unsigned char *cp = (unsigned char *)buf; + +#ifdef HAVE_GETRANDOM + while (getrandom(buf, nbytes, 0) < 0) { + if (errno == EINTR) + continue; + break; + } +#else + size_t n = nbytes; int fd = random_get_fd(); int lose_counter = 0; - unsigned char *cp = (unsigned char *) buf; if (fd >= 0) { while (n > 0) { @@ -92,11 +125,12 @@ void random_get_bytes(void *buf, size_t nbytes) close(fd); } - +#endif /* * We do this all the time, but this is the only source of * randomness if /dev/random/urandom is out to lunch. */ + crank_random(); for (cp = buf, i = 0; i < nbytes; i++) *cp++ ^= (rand() >> 7) & 0xFF; @@ -122,6 +156,9 @@ void random_get_bytes(void *buf, size_t nbytes) */ const char *random_tell_source(void) { +#ifdef HAVE_GETRANDOM + return _("getrandom() function"); +#else size_t i; static const char *random_sources[] = { "/dev/urandom", @@ -132,7 +169,7 @@ const char *random_tell_source(void) if (!access(random_sources[i], R_OK)) return random_sources[i]; } - +#endif return _("libc pseudo-random functions"); }