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util/nvmutil: don't use /dev/urandom

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too over engineered and cumbersome.

the new security in prw() makes it brittle,
and i'd rather not move checks outside of it.

the fallback rand is random enough.

Signed-off-by: Leah Rowe <leah@libreboot.org>
This commit is contained in:
Leah Rowe
2026-03-14 18:11:48 +00:00
parent fac0017532
commit cde085d54e
1 changed files with 4 additions and 54 deletions
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58
util/nvmutil/nvmutil.c
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@@ -289,12 +289,7 @@ static int xstrxcmp(const char *a, const char *b, size_t maxlen);
/*
* Prep files for reading
*
* Portability: /dev/urandom used
* on Linux / old Unix, whereas
* arc4random is used on BSD/MacOS.
*/
static void open_dev_urandom(void);
static void open_gbe_file(void);
static void lock_gbe_file(void);
static void xopen(int *fd, const char *path, int flags, struct stat *st);
@@ -328,7 +323,6 @@ static void set_mac_nib(size_t mac_str_pos,
size_t mac_byte_pos, size_t mac_nib_pos);
static ushort hextonum(char ch_s);
static ushort rhex(void);
static ushort fallback_rand(void);
static ulong entropy_jitter(void);
static void write_mac_part(size_t partnum);
@@ -441,9 +435,6 @@ static u8 rnum[NUM_RANDOM_BYTES];
*/
#define items(x) (sizeof((x)) / sizeof((x)[0]))
static const char newrandom[] = "/dev/urandom";
static const char *rname = NULL;
/*
* GbE files can be 8KB, 16KB or 128KB,
* but we only need the two 4KB parts
@@ -460,7 +451,6 @@ static u8 *buf = real_buf;
static ushort mac_buf[3];
static off_t gbe_file_size;
static int urandom_fd = -1;
static int gbe_fd = -1;
static size_t part;
static u8 part_modified[2];
@@ -655,8 +645,6 @@ typedef char bool_loop_eagain[(LOOP_EAGAIN==1||LOOP_EAGAIN==0)?1:-1];
typedef char bool_no_loop_eintr[(NO_LOOP_EINTR==0)?1:-1];
typedef char bool_no_loop_eagain[(NO_LOOP_EAGAIN==0)?1:-1];
static int use_prng = 0;
static int io_err_gbe = 0;
static int rw_check_err_read[] = {0, 0};
static int rw_check_partial_read[] = {0, 0};
@@ -677,8 +665,8 @@ main(int argc, char *argv[])
#ifdef NVMUTIL_UNVEIL
if (pledge("stdio rpath wpath unveil", NULL) == -1)
err(errno, "pledge");
if (unveil("/dev/urandom", "r") == -1)
err(errno, "unveil /dev/urandom");
if (unveil("/dev/null", "r") == -1)
err(errno, "unveil /dev/null");
#else
if (pledge("stdio rpath wpath", NULL) == -1)
err(errno, "pledge");
@@ -715,7 +703,7 @@ main(int argc, char *argv[])
#endif
#endif
open_dev_urandom();
srand((uint)(time(NULL) ^ getpid()));
open_gbe_file();
lock_gbe_file();
@@ -933,19 +921,6 @@ xstrxcmp(const char *a, const char *b, size_t maxlen)
return -1;
}
static void
open_dev_urandom(void)
{
rname = newrandom;
urandom_fd = open(rname, O_RDONLY);
if (urandom_fd != -1)
return;
/* fallback on VERY VERY VERY old unix */
use_prng = 1;
srand((uint)(time(NULL) ^ getpid()));
}
static void
open_gbe_file(void)
{
@@ -1249,24 +1224,6 @@ hextonum(char ch_s)
static ushort
rhex(void)
{
static size_t n = 0;
if (use_prng)
return fallback_rand();
if (!n) {
n = sizeof(rnum);
if (rw_file_exact(urandom_fd, rnum, n, 0, IO_READ,
NO_LOOP_EAGAIN, LOOP_EINTR, MAX_ZERO_RW_RETRY) == -1)
err(errno, "Randomisation failed");
}
return (ushort)(rnum[--n] & 0xf);
}
static ushort
fallback_rand(void)
{
struct timeval tv;
ulong mix;
@@ -2154,7 +2111,6 @@ static int
close_files(void)
{
int close_err_gbe = 0;
int close_err_rand = 0;
int saved_errno = errno;
if (gbe_fd > -1) {
@@ -2163,16 +2119,10 @@ close_files(void)
gbe_fd = -1;
}
if (urandom_fd > -1) {
if (close(urandom_fd) == -1)
close_err_rand = errno;
urandom_fd = -1;
}
if (saved_errno)
errno = saved_errno;
if (close_err_gbe || close_err_rand)
if (close_err_gbe)
return -1;
return 0;