The mcookie should reuse existing code, and there is definitely no need to prefer /dev/random for this utility. See reference for explanation about later statement. References: http://www.2uo.de/myths-about-urandom/ Signed-off-by: Sami Kerola <kerolasa@xxxxxx> --- include/randutils.h | 1 + lib/randutils.c | 19 ++++++++++++++++ misc-utils/Makemodule.am | 1 + misc-utils/mcookie.1 | 45 +++++++++++++++----------------------- misc-utils/mcookie.c | 57 +++++++++--------------------------------------- 5 files changed, 48 insertions(+), 75 deletions(-) diff --git a/include/randutils.h b/include/randutils.h index dec5e35..17e2a02 100644 --- a/include/randutils.h +++ b/include/randutils.h @@ -8,5 +8,6 @@ extern int random_get_fd(void); extern void random_get_bytes(void *buf, size_t nbytes); +extern const char *random_tell_source(void); #endif diff --git a/lib/randutils.c b/lib/randutils.c index 68bb0e1..7c49fd7 100644 --- a/lib/randutils.c +++ b/lib/randutils.c @@ -108,6 +108,25 @@ void random_get_bytes(void *buf, size_t nbytes) return; } + +/* + * Tell source of randomness. + */ +const char *random_tell_source(void) +{ + const char *random_sources[] = { + "/dev/urandom", + "/dev/random", + "glibc pseudo-random functions" + }; + + if (!access(random_sources[0], R_OK)) + return random_sources[0]; + if (!access(random_sources[1], R_OK)) + return random_sources[1]; + return random_sources[2]; +} + #ifdef TEST_PROGRAM int main(int argc __attribute__((__unused__)), char *argv[] __attribute__((__unused__))) diff --git a/misc-utils/Makemodule.am b/misc-utils/Makemodule.am index 05407de..f31e4e1 100644 --- a/misc-utils/Makemodule.am +++ b/misc-utils/Makemodule.am @@ -32,6 +32,7 @@ look_SOURCES = misc-utils/look.c usrbin_exec_PROGRAMS += mcookie dist_man_MANS += misc-utils/mcookie.1 mcookie_SOURCES = misc-utils/mcookie.c lib/md5.c +mcookie_LDADD = $(LDADD) libcommon.la usrbin_exec_PROGRAMS += namei dist_man_MANS += misc-utils/namei.1 diff --git a/misc-utils/mcookie.1 b/misc-utils/mcookie.1 index fc7e030..df6137f 100644 --- a/misc-utils/mcookie.1 +++ b/misc-utils/mcookie.1 @@ -1,6 +1,6 @@ .\" mcookie.1 -- .\" Public Domain 1995 Rickard E. Faith (faith@xxxxxxxxxx) -.TH MCOOKIE 1 "June 2011" "util-linux" "User Commands" +.TH MCOOKIE 1 "March 2014" "util-linux" "User Commands" .SH NAME mcookie \- generate magic cookies for xauth .SH SYNOPSIS @@ -15,23 +15,21 @@ xauth add :0 . `mcookie` .RE .PP The "random" number generated is actually the output of the MD5 message -digest fed with various pieces of random information: the current time, the -process id, the parent process id, and optionally the contents of an input -file. and several bytes of information from the first of the following -devices which is present: -.IR /dev/random , +digest fed with random information from one of the sources .IR /dev/urandom , -files in -.IR /proc , -.IR /dev/audio . +.IR /dev/random , +or +.I "glibc pseudo-random functions" +in this preference order. .SH OPTIONS .TP \fB\-f\fR, \fB\-\-file\fR=\fIFILE\fR -Use file as a macig cookie seed. When file is defined as `-' character -input is read from stdin. +Use additional file as a macig cookie random seed. When file is defined +as '-' character input is read from stdin. .TP \fB\-v\fR, \fB\-\-verbose\fR -Explain what is being done. +Inform where randomness originated, with amount of entropy read from each +source. .TP \fB\-V\fR, \fB\-\-version\fR Display version information and exit. @@ -39,27 +37,18 @@ Display version information and exit. \fB\-h\fR, \fB\-\-help\fR Display help text and exit. .SH BUGS -The entropy in the generated 128-bit is probably quite small (and, -therefore, vulnerable to attack) unless a non-pseudorandom number generator -is used (e.g., -.I /dev/random -under Linux). -.PP -It is assumed that none of the devices opened will block. +It is assumed that none of the randomness sources will block. .SH FILES -.I /dev/random -.br .I /dev/urandom .br -.I /dev/audio -.br -.I /proc/stat -.br -.I /proc/loadavg +.I /dev/random .SH "SEE ALSO" .BR X (1), .BR xauth (1), -.BR md5sum (1) +.BR md5sum (1), +.BR rand (3) .SH AVAILABILITY The mcookie command is part of the util-linux package and is available from -ftp://ftp.kernel.org/pub/linux/utils/util-linux/. +.UR ftp://\:ftp.kernel.org\:/pub\:/linux\:/utils\:/util-linux/ +Linux Kernel Archive +.UE . diff --git a/misc-utils/mcookie.c b/misc-utils/mcookie.c index d7af3c2..63eeb5b 100644 --- a/misc-utils/mcookie.c +++ b/misc-utils/mcookie.c @@ -22,6 +22,7 @@ #include "md5.h" #include "nls.h" #include "closestream.h" +#include "randutils.h" #include <fcntl.h> #include <getopt.h> @@ -31,21 +32,11 @@ #include <sys/time.h> #include <unistd.h> -#define BUFFERSIZE 4096 - -struct rngs { - const char *path; - int minlength, maxlength; -} rngs[] = { - {"/dev/random", 16, 16}, /* 16 bytes = 128 bits suffice */ - {"/proc/interrupts", 0, 0}, - {"/proc/slabinfo", 0, 0}, - {"/proc/stat", 0, 0}, - {"/dev/urandom", 32, 64}, +enum { + BUFFERSIZE = 4096, + RAND_BYTES = 128 }; -#define RNGS (sizeof(rngs)/sizeof(struct rngs)) - /* The basic function to hash a file */ static off_t hash_file(struct MD5Context *ctx, int fd) { @@ -83,15 +74,11 @@ int main(int argc, char **argv) size_t i; struct MD5Context ctx; unsigned char digest[MD5LENGTH]; - unsigned char buf[BUFFERSIZE]; + unsigned char buf[RAND_BYTES]; int fd; int c; - pid_t pid; char *file = NULL; int verbose = 0; - int r; - struct timeval tv; - struct timezone tz; static const struct option longopts[] = { {"file", required_argument, NULL, 'f'}, @@ -125,13 +112,6 @@ int main(int argc, char **argv) } MD5Init(&ctx); - gettimeofday(&tv, &tz); - MD5Update(&ctx, (unsigned char *) &tv, sizeof(tv)); - - pid = getppid(); - MD5Update(&ctx, (unsigned char *) &pid, sizeof(pid)); - pid = getpid(); - MD5Update(&ctx, (unsigned char *) &pid, sizeof(pid)); if (file) { int count = 0; @@ -158,28 +138,11 @@ int main(int argc, char **argv) } } - for (i = 0; i < RNGS; i++) { - if ((fd = open(rngs[i].path, O_RDONLY | O_NONBLOCK)) >= 0) { - int count = sizeof(buf); - - if (rngs[i].maxlength && count > rngs[i].maxlength) - count = rngs[i].maxlength; - r = read(fd, buf, count); - if (r > 0) - MD5Update(&ctx, buf, r); - else - r = 0; - close(fd); - if (verbose) - fprintf(stderr, - P_("Got %d byte from %s\n", - "Got %d bytes from %s\n", r), - r, rngs[i].path); - if (rngs[i].minlength && r >= rngs[i].minlength) - break; - } else if (verbose) - warn(_("cannot open %s"), rngs[i].path); - } + random_get_bytes(&buf, RAND_BYTES); + MD5Update(&ctx, buf, RAND_BYTES); + if (verbose) + fprintf(stderr, + _("Got %d bytes from %s\n"), RAND_BYTES, random_tell_source()); MD5Final(digest, &ctx); for (i = 0; i < MD5LENGTH; i++) -- 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
