0c69794138
These lines are generally out-of-date, incomplete and unnecessary. With SPDX and git repository much more accurate and fine grained information about licensing and authorship is available, hence let's drop the per-file copyright notice. Of course, removing copyright lines of others is problematic, hence this commit only removes my own lines and leaves all others untouched. It might be nicer if sooner or later those could go away too, making git the only and accurate source of authorship information.
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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