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util/nvmutil: fallback randomiser

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used when a random device isn't available, on old
unix, or on certain chroot environments.

Signed-off-by: Leah Rowe <leah@libreboot.org>
This commit is contained in:
Leah Rowe
2026-03-12 14:10:29 +00:00
parent 5ba0b98fbc
commit 53c5a40007
1 changed files with 35 additions and 0 deletions
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util/nvmutil/nvmutil.c
+35
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@@ -26,6 +26,7 @@
#ifdef __OpenBSD__ #ifdef __OpenBSD__
#include <sys/param.h> #include <sys/param.h>
#endif #endif
#include <sys/time.h>
#include <sys/types.h> #include <sys/types.h>
#include <sys/stat.h> #include <sys/stat.h>
@@ -51,6 +52,7 @@ typedef unsigned int uint32_t;
#include <stdio.h> #include <stdio.h>
#include <stdlib.h> #include <stdlib.h>
#include <string.h> #include <string.h>
#include <time.h>
#include <unistd.h> #include <unistd.h>
typedef char static_assert_char_is_8_bits[(CHAR_BIT == 8) ? 1 : -1]; typedef char static_assert_char_is_8_bits[(CHAR_BIT == 8) ? 1 : -1];
@@ -161,6 +163,7 @@ static void set_mac_nib(size_t mac_str_pos,
size_t mac_byte_pos, size_t mac_nib_pos); size_t mac_byte_pos, size_t mac_nib_pos);
static uint16_t hextonum(char ch_s); static uint16_t hextonum(char ch_s);
static uint16_t rhex(void); static uint16_t rhex(void);
static uint16_t fallback_rand(void);
static void write_mac_part(size_t partnum); static void write_mac_part(size_t partnum);
/* /*
@@ -434,6 +437,8 @@ static size_t cmd_index = CMD_NULL;
typedef char assert_argc3[(ARGC_3==3)?1:-1]; typedef char assert_argc3[(ARGC_3==3)?1:-1];
typedef char assert_argc4[(ARGC_4==4)?1:-1]; typedef char assert_argc4[(ARGC_4==4)?1:-1];
static int use_prng = 0;
int int
main(int argc, char *argv[]) main(int argc, char *argv[])
{ {
@@ -720,6 +725,12 @@ open_dev_urandom(void)
rname = oldrandom; rname = oldrandom;
urandom_fd = open(rname, O_RDONLY); urandom_fd = open(rname, O_RDONLY);
if (urandom_fd != -1)
return;
/* fallback on VERY VERY VERY old unix */
use_prng = 1;
srand((unsigned)(time(NULL) ^ getpid()));
} }
static void static void
@@ -996,6 +1007,14 @@ rhex(void)
static size_t n = 0; static size_t n = 0;
static uint8_t rnum[12]; static uint8_t rnum[12];
if (use_prng) {
/*
* On very old Unix systems that
* lack /dev/random and /dev/urandom
*/
return fallback_rand();
}
if (urandom_fd < 0) if (urandom_fd < 0)
err(ECANCELED, "Your operating system has no /dev/[u]random"); err(ECANCELED, "Your operating system has no /dev/[u]random");
@@ -1008,6 +1027,22 @@ rhex(void)
return (uint16_t)(rnum[--n] & 0xf); return (uint16_t)(rnum[--n] & 0xf);
} }
static uint16_t
fallback_rand(void)
{
struct timeval tv;
unsigned long mix;
gettimeofday(&tv, NULL);
mix = (unsigned long)tv.tv_sec
^ (unsigned long)tv.tv_usec
^ (unsigned long)getpid()
^ (unsigned long)(uintptr_t)&mix;
return (uint16_t)(mix & 0xf);
}
static void static void
write_mac_part(size_t partnum) write_mac_part(size_t partnum)
{ {