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util/nvmutil: allow partial reads of /dev/urandom

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Signed-off-by: Leah Rowe <leah@libreboot.org>
This commit is contained in:
Leah Rowe
2026-03-09 06:00:41 +00:00
parent e092b2ce0b
commit dbc7fadcbc
1 changed files with 28 additions and 8 deletions
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util/nvmutil/nvmutil.c
+28 -8
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@@ -89,7 +89,7 @@ static void set_mac_nib(size_t mac_str_pos,
size_t mac_byte_pos, size_t mac_nib_pos);
static uint16_t hextonum(char ch_s);
static uint16_t rhex(void);
static void read_file_exact(int fd, void *buf, size_t len,
static ssize_t read_gbe_file_exact(int fd, void *buf, size_t len,
off_t off, const char *path, const char *op);
static void write_mac_part(size_t partnum);
static void cmd_helper_dump(void);
@@ -691,8 +691,10 @@ read_gbe_file_part(size_t p)
void *mem_offset =
gbe_mem_offset(p ^ command[cmd_index].invert, "pread");
read_file_exact(gbe_fd, mem_offset,
gbe_rw_size, gbe_file_offset(p, "pread"), fname, "pread");
if ((size_t)read_gbe_file_exact(gbe_fd, mem_offset,
gbe_rw_size, gbe_file_offset(p, "pread"), fname, "pread") !=
gbe_rw_size)
err(ECANCELED, "Partial read p%zu, file %s", p, fname);
printf("Read %zu bytes from part %zu: %s\n",
gbe_rw_size, p, fname);
@@ -913,15 +915,16 @@ rhex(void)
#ifdef NVMUTIL_ARC4RANDOM_BUF
arc4random_buf(rnum, n);
#else
read_file_exact(urandom_fd, rnum, n, 0, rname, NULL);
n = (size_t)read_gbe_file_exact(urandom_fd,
rnum, n, 0, rname, NULL);
#endif
}
return (uint16_t)(rnum[--n] & 0xf);
}
static void
read_file_exact(int fd, void *buf, size_t len,
static ssize_t
read_gbe_file_exact(int fd, void *buf, size_t len,
off_t off, const char *path, const char *op)
{
int retry;
@@ -938,13 +941,29 @@ read_file_exact(int fd, void *buf, size_t len,
if (rval == (ssize_t)len) {
errno = 0;
return;
return rval;
}
if (rval != -1)
if (rval != -1) {
if (path == oldrandom || path == newrandom) {
/*
* /dev/[u]random reads can still return
* partial reads legally, on some weird
* Unix systems (especially older ones).
*
* We use a circular buffer for random
* bytes in rhex(), so we can just use
* the smaller amount of bytes and call
* read_gbe_file_exact again if necessary.
*/
if (rval > 0)
return rval;
}
err(ECANCELED,
"Short %s, %zd bytes, on file: %s",
op ? op : "read", rval, path);
}
if (errno != EINTR)
err(ECANCELED,
@@ -954,6 +973,7 @@ read_file_exact(int fd, void *buf, size_t len,
err(EINTR, "%s: max retries exceeded on file: %s",
op ? op : "read", path);
return -1;
}
static void