362 lines
11 KiB
C
362 lines
11 KiB
C
/* SPDX-License-Identifier: LGPL-2.1+ */
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#include <errno.h>
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#include <grp.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/capability.h>
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#include <sys/prctl.h>
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#include <unistd.h>
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#include "alloc-util.h"
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#include "capability-util.h"
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#include "fileio.h"
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#include "log.h"
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#include "macro.h"
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#include "parse-util.h"
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#include "user-util.h"
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#include "util.h"
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int have_effective_cap(int value) {
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_cleanup_cap_free_ cap_t cap;
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cap_flag_value_t fv;
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cap = cap_get_proc();
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if (!cap)
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return -errno;
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if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0)
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return -errno;
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else
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return fv == CAP_SET;
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}
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unsigned long cap_last_cap(void) {
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static thread_local unsigned long saved;
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static thread_local bool valid = false;
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_cleanup_free_ char *content = NULL;
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unsigned long p = 0;
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int r;
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if (valid)
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return saved;
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/* available since linux-3.2 */
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r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content);
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if (r >= 0) {
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r = safe_atolu(content, &p);
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if (r >= 0) {
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saved = p;
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valid = true;
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return p;
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}
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}
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/* fall back to syscall-probing for pre linux-3.2 */
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p = (unsigned long) CAP_LAST_CAP;
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if (prctl(PR_CAPBSET_READ, p) < 0) {
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/* Hmm, look downwards, until we find one that
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* works */
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for (p--; p > 0; p --)
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if (prctl(PR_CAPBSET_READ, p) >= 0)
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break;
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} else {
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/* Hmm, look upwards, until we find one that doesn't
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* work */
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for (;; p++)
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if (prctl(PR_CAPBSET_READ, p+1) < 0)
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break;
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}
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saved = p;
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valid = true;
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return p;
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}
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int capability_update_inherited_set(cap_t caps, uint64_t set) {
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unsigned long i;
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/* Add capabilities in the set to the inherited caps. Do not apply
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* them yet. */
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for (i = 0; i < cap_last_cap(); i++) {
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if (set & (UINT64_C(1) << i)) {
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cap_value_t v;
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v = (cap_value_t) i;
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/* Make the capability inheritable. */
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if (cap_set_flag(caps, CAP_INHERITABLE, 1, &v, CAP_SET) < 0)
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return -errno;
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}
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}
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return 0;
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}
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int capability_ambient_set_apply(uint64_t set, bool also_inherit) {
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unsigned long i;
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_cleanup_cap_free_ cap_t caps = NULL;
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/* Add the capabilities to the ambient set. */
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if (also_inherit) {
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int r;
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caps = cap_get_proc();
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if (!caps)
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return -errno;
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r = capability_update_inherited_set(caps, set);
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if (r < 0)
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return -errno;
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if (cap_set_proc(caps) < 0)
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return -errno;
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}
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for (i = 0; i < cap_last_cap(); i++) {
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if (set & (UINT64_C(1) << i)) {
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/* Add the capability to the ambient set. */
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if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) < 0)
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return -errno;
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}
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}
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return 0;
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}
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int capability_bounding_set_drop(uint64_t keep, bool right_now) {
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_cleanup_cap_free_ cap_t before_cap = NULL, after_cap = NULL;
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cap_flag_value_t fv;
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unsigned long i;
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int r;
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/* If we are run as PID 1 we will lack CAP_SETPCAP by default
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* in the effective set (yes, the kernel drops that when
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* executing init!), so get it back temporarily so that we can
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* call PR_CAPBSET_DROP. */
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before_cap = cap_get_proc();
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if (!before_cap)
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return -errno;
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if (cap_get_flag(before_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0)
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return -errno;
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if (fv != CAP_SET) {
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_cleanup_cap_free_ cap_t temp_cap = NULL;
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static const cap_value_t v = CAP_SETPCAP;
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temp_cap = cap_dup(before_cap);
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if (!temp_cap)
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return -errno;
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if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0)
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return -errno;
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if (cap_set_proc(temp_cap) < 0)
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log_debug_errno(errno, "Can't acquire effective CAP_SETPCAP bit, ignoring: %m");
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/* If we didn't manage to acquire the CAP_SETPCAP bit, we continue anyway, after all this just means
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* we'll fail later, when we actually intend to drop some capabilities. */
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}
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after_cap = cap_dup(before_cap);
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if (!after_cap)
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return -errno;
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for (i = 0; i <= cap_last_cap(); i++) {
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cap_value_t v;
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if ((keep & (UINT64_C(1) << i)))
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continue;
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/* Drop it from the bounding set */
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if (prctl(PR_CAPBSET_DROP, i) < 0) {
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r = -errno;
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/* If dropping the capability failed, let's see if we didn't have it in the first place. If so,
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* continue anyway, as dropping a capability we didn't have in the first place doesn't really
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* matter anyway. */
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if (prctl(PR_CAPBSET_READ, i) != 0)
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goto finish;
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}
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v = (cap_value_t) i;
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/* Also drop it from the inheritable set, so
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* that anything we exec() loses the
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* capability for good. */
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if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
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r = -errno;
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goto finish;
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}
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/* If we shall apply this right now drop it
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* also from our own capability sets. */
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if (right_now) {
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if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
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cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
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r = -errno;
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goto finish;
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}
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}
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}
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r = 0;
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finish:
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if (cap_set_proc(after_cap) < 0) {
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/* If there are no actual changes anyway then let's ignore this error. */
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if (cap_compare(before_cap, after_cap) != 0)
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r = -errno;
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}
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return r;
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}
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static int drop_from_file(const char *fn, uint64_t keep) {
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_cleanup_free_ char *p = NULL;
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uint64_t current, after;
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uint32_t hi, lo;
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int r, k;
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r = read_one_line_file(fn, &p);
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if (r < 0)
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return r;
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assert_cc(sizeof(hi) == sizeof(unsigned));
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assert_cc(sizeof(lo) == sizeof(unsigned));
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k = sscanf(p, "%u %u", &lo, &hi);
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if (k != 2)
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return -EIO;
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current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
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after = current & keep;
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if (current == after)
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return 0;
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lo = (unsigned) (after & 0xFFFFFFFFULL);
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hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
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return write_string_filef(fn, WRITE_STRING_FILE_CREATE, "%u %u", lo, hi);
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}
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int capability_bounding_set_drop_usermode(uint64_t keep) {
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int r;
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r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", keep);
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if (r < 0)
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return r;
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r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", keep);
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if (r < 0)
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return r;
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return r;
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}
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int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
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_cleanup_cap_free_ cap_t d = NULL;
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unsigned i, j = 0;
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int r;
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/* Unfortunately we cannot leave privilege dropping to PID 1
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* here, since we want to run as user but want to keep some
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* capabilities. Since file capabilities have been introduced
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* this cannot be done across exec() anymore, unless our
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* binary has the capability configured in the file system,
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* which we want to avoid. */
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if (setresgid(gid, gid, gid) < 0)
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return log_error_errno(errno, "Failed to change group ID: %m");
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r = maybe_setgroups(0, NULL);
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if (r < 0)
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return log_error_errno(r, "Failed to drop auxiliary groups list: %m");
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/* Ensure we keep the permitted caps across the setresuid() */
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if (prctl(PR_SET_KEEPCAPS, 1) < 0)
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return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
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if (setresuid(uid, uid, uid) < 0)
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return log_error_errno(errno, "Failed to change user ID: %m");
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if (prctl(PR_SET_KEEPCAPS, 0) < 0)
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return log_error_errno(errno, "Failed to disable keep capabilities flag: %m");
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/* Drop all caps from the bounding set, except the ones we want */
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r = capability_bounding_set_drop(keep_capabilities, true);
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if (r < 0)
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return log_error_errno(r, "Failed to drop capabilities: %m");
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/* Now upgrade the permitted caps we still kept to effective caps */
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d = cap_init();
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if (!d)
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return log_oom();
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if (keep_capabilities) {
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cap_value_t bits[u64log2(keep_capabilities) + 1];
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for (i = 0; i < ELEMENTSOF(bits); i++)
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if (keep_capabilities & (1ULL << i))
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bits[j++] = i;
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/* use enough bits */
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assert(i == 64 || (keep_capabilities >> i) == 0);
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/* don't use too many bits */
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assert(keep_capabilities & (1ULL << (i - 1)));
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if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
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cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0)
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return log_error_errno(errno, "Failed to enable capabilities bits: %m");
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if (cap_set_proc(d) < 0)
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return log_error_errno(errno, "Failed to increase capabilities: %m");
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}
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return 0;
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}
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int drop_capability(cap_value_t cv) {
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_cleanup_cap_free_ cap_t tmp_cap = NULL;
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tmp_cap = cap_get_proc();
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if (!tmp_cap)
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return -errno;
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if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, CAP_CLEAR) < 0) ||
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(cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) ||
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(cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0))
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return -errno;
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if (cap_set_proc(tmp_cap) < 0)
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return -errno;
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return 0;
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}
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bool ambient_capabilities_supported(void) {
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static int cache = -1;
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if (cache >= 0)
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return cache;
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/* If PR_CAP_AMBIENT returns something valid, or an unexpected error code we assume that ambient caps are
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* available. */
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cache = prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_KILL, 0, 0) >= 0 ||
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!IN_SET(errno, EINVAL, EOPNOTSUPP, ENOSYS);
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return cache;
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}
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