f0d09059bd
During early boot, we'd call getrandom(), and immediately fall back to reading from /dev/urandom unless we got the full requested number of bytes. Those two sources are the same, so the most likely result is /dev/urandom producing some pseudorandom numbers for us, complaining widely on the way. Let's change our behaviour to be more conservative: - if the numbers are only used to initialize a hash table, a short read is OK, we don't really care if we get the first part of the seed truly random and then some pseudorandom bytes. So just do that and return "success". - if getrandom() returns -EAGAIN, fall back to rand() instead of querying /dev/urandom again. The idea with those two changes is to avoid generating a warning about reading from an /dev/urandom when the kernel doesn't have enough entropy. - only in the cases where we really need to make the best effort possible (sd_id128_randomize and firstboot password hashing), fall back to /dev/urandom. When calling getrandom(), drop the checks whether the argument fits in an int — getrandom() should do that for us already, and we call it with small arguments only anyway. Note that this does not really change the (relatively high) number of random bytes we request from the kernel. On my laptop, during boot, PID 1 and all other processes using this code through libsystemd request: 74780 bytes with high_quality_required == false 464 bytes with high_quality_required == true and it does not eliminate reads from /dev/urandom completely. If the kernel was short on entropy and getrandom() would fail, we would fall back to /dev/urandom for those 464 bytes. When falling back to /dev/urandom, don't lose the short read we already got, and just read the remaining bytes. If getrandom() syscall is not available, we fall back to /dev/urandom same as before. Fixes #4167 (possibly partially, let's see).
334 lines
9.3 KiB
C
334 lines
9.3 KiB
C
/***
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This file is part of systemd.
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Copyright 2011 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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***/
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#include <errno.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include "sd-id128.h"
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#include "alloc-util.h"
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#include "fd-util.h"
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#include "hexdecoct.h"
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#include "id128-util.h"
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#include "io-util.h"
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#include "khash.h"
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#include "macro.h"
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#include "missing.h"
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#include "random-util.h"
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#include "user-util.h"
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#include "util.h"
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_public_ char *sd_id128_to_string(sd_id128_t id, char s[SD_ID128_STRING_MAX]) {
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unsigned n;
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assert_return(s, NULL);
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for (n = 0; n < 16; n++) {
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s[n*2] = hexchar(id.bytes[n] >> 4);
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s[n*2+1] = hexchar(id.bytes[n] & 0xF);
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}
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s[32] = 0;
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return s;
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}
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_public_ int sd_id128_from_string(const char s[], sd_id128_t *ret) {
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unsigned n, i;
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sd_id128_t t;
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bool is_guid = false;
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assert_return(s, -EINVAL);
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for (n = 0, i = 0; n < 16;) {
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int a, b;
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if (s[i] == '-') {
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/* Is this a GUID? Then be nice, and skip over
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* the dashes */
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if (i == 8)
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is_guid = true;
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else if (i == 13 || i == 18 || i == 23) {
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if (!is_guid)
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return -EINVAL;
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} else
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return -EINVAL;
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i++;
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continue;
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}
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a = unhexchar(s[i++]);
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if (a < 0)
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return -EINVAL;
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b = unhexchar(s[i++]);
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if (b < 0)
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return -EINVAL;
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t.bytes[n++] = (a << 4) | b;
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}
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if (i != (is_guid ? 36 : 32))
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return -EINVAL;
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if (s[i] != 0)
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return -EINVAL;
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if (ret)
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*ret = t;
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return 0;
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}
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_public_ int sd_id128_get_machine(sd_id128_t *ret) {
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static thread_local sd_id128_t saved_machine_id = {};
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int r;
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assert_return(ret, -EINVAL);
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if (sd_id128_is_null(saved_machine_id)) {
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r = id128_read("/etc/machine-id", ID128_PLAIN, &saved_machine_id);
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if (r < 0)
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return r;
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if (sd_id128_is_null(saved_machine_id))
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return -EINVAL;
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}
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*ret = saved_machine_id;
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return 0;
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}
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_public_ int sd_id128_get_boot(sd_id128_t *ret) {
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static thread_local sd_id128_t saved_boot_id = {};
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int r;
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assert_return(ret, -EINVAL);
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if (sd_id128_is_null(saved_boot_id)) {
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r = id128_read("/proc/sys/kernel/random/boot_id", ID128_UUID, &saved_boot_id);
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if (r < 0)
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return r;
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}
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*ret = saved_boot_id;
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return 0;
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}
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static int get_invocation_from_keyring(sd_id128_t *ret) {
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_cleanup_free_ char *description = NULL;
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char *d, *p, *g, *u, *e;
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unsigned long perms;
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key_serial_t key;
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size_t sz = 256;
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uid_t uid;
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gid_t gid;
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int r, c;
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#define MAX_PERMS ((unsigned long) (KEY_POS_VIEW|KEY_POS_READ|KEY_POS_SEARCH| \
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KEY_USR_VIEW|KEY_USR_READ|KEY_USR_SEARCH))
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assert(ret);
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key = request_key("user", "invocation_id", NULL, 0);
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if (key == -1) {
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/* Keyring support not available? No invocation key stored? */
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if (IN_SET(errno, ENOSYS, ENOKEY))
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return 0;
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return -errno;
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}
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for (;;) {
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description = new(char, sz);
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if (!description)
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return -ENOMEM;
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c = keyctl(KEYCTL_DESCRIBE, key, (unsigned long) description, sz, 0);
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if (c < 0)
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return -errno;
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if ((size_t) c <= sz)
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break;
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sz = c;
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free(description);
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}
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/* The kernel returns a final NUL in the string, verify that. */
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assert(description[c-1] == 0);
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/* Chop off the final description string */
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d = strrchr(description, ';');
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if (!d)
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return -EIO;
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*d = 0;
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/* Look for the permissions */
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p = strrchr(description, ';');
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if (!p)
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return -EIO;
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errno = 0;
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perms = strtoul(p + 1, &e, 16);
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if (errno > 0)
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return -errno;
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if (e == p + 1) /* Read at least one character */
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return -EIO;
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if (e != d) /* Must reached the end */
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return -EIO;
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if ((perms & ~MAX_PERMS) != 0)
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return -EPERM;
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*p = 0;
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/* Look for the group ID */
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g = strrchr(description, ';');
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if (!g)
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return -EIO;
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r = parse_gid(g + 1, &gid);
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if (r < 0)
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return r;
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if (gid != 0)
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return -EPERM;
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*g = 0;
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/* Look for the user ID */
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u = strrchr(description, ';');
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if (!u)
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return -EIO;
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r = parse_uid(u + 1, &uid);
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if (r < 0)
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return r;
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if (uid != 0)
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return -EPERM;
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c = keyctl(KEYCTL_READ, key, (unsigned long) ret, sizeof(sd_id128_t), 0);
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if (c < 0)
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return -errno;
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if (c != sizeof(sd_id128_t))
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return -EIO;
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return 1;
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}
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_public_ int sd_id128_get_invocation(sd_id128_t *ret) {
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static thread_local sd_id128_t saved_invocation_id = {};
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int r;
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assert_return(ret, -EINVAL);
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if (sd_id128_is_null(saved_invocation_id)) {
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/* We first try to read the invocation ID from the kernel keyring. This has the benefit that it is not
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* fakeable by unprivileged code. If the information is not available in the keyring, we use
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* $INVOCATION_ID but ignore the data if our process was called by less privileged code
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* (i.e. secure_getenv() instead of getenv()).
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*
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* The kernel keyring is only relevant for system services (as for user services we don't store the
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* invocation ID in the keyring, as there'd be no trust benefit in that). The environment variable is
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* primarily relevant for user services, and sufficiently safe as no privilege boundary is involved. */
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r = get_invocation_from_keyring(&saved_invocation_id);
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if (r < 0)
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return r;
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if (r == 0) {
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const char *e;
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e = secure_getenv("INVOCATION_ID");
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if (!e)
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return -ENXIO;
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r = sd_id128_from_string(e, &saved_invocation_id);
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if (r < 0)
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return r;
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}
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}
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*ret = saved_invocation_id;
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return 0;
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}
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static sd_id128_t make_v4_uuid(sd_id128_t id) {
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/* Stolen from generate_random_uuid() of drivers/char/random.c
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* in the kernel sources */
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/* Set UUID version to 4 --- truly random generation */
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id.bytes[6] = (id.bytes[6] & 0x0F) | 0x40;
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/* Set the UUID variant to DCE */
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id.bytes[8] = (id.bytes[8] & 0x3F) | 0x80;
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return id;
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}
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_public_ int sd_id128_randomize(sd_id128_t *ret) {
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sd_id128_t t;
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int r;
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assert_return(ret, -EINVAL);
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r = acquire_random_bytes(&t, sizeof t, true);
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if (r < 0)
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return r;
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/* Turn this into a valid v4 UUID, to be nice. Note that we
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* only guarantee this for newly generated UUIDs, not for
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* pre-existing ones. */
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*ret = make_v4_uuid(t);
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return 0;
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}
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_public_ int sd_id128_get_machine_app_specific(sd_id128_t app_id, sd_id128_t *ret) {
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_cleanup_(khash_unrefp) khash *h = NULL;
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sd_id128_t m, result;
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const void *p;
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int r;
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assert_return(ret, -EINVAL);
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r = sd_id128_get_machine(&m);
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if (r < 0)
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return r;
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r = khash_new_with_key(&h, "hmac(sha256)", &m, sizeof(m));
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if (r < 0)
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return r;
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r = khash_put(h, &app_id, sizeof(app_id));
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if (r < 0)
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return r;
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r = khash_digest_data(h, &p);
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if (r < 0)
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return r;
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/* We chop off the trailing 16 bytes */
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memcpy(&result, p, MIN(khash_get_size(h), sizeof(result)));
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*ret = make_v4_uuid(result);
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return 0;
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}
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