| /* SPDX-License-Identifier: LGPL-2.1-or-later */ |
| |
| #include <errno.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <sys/prctl.h> |
| #include <unistd.h> |
| |
| #include "alloc-util.h" |
| #include "capability-util.h" |
| #include "cap-list.h" |
| #include "fileio.h" |
| #include "log.h" |
| #include "logarithm.h" |
| #include "macro.h" |
| #include "missing_prctl.h" |
| #include "missing_threads.h" |
| #include "parse-util.h" |
| #include "user-util.h" |
| |
| int have_effective_cap(int value) { |
| _cleanup_cap_free_ cap_t cap = NULL; |
| cap_flag_value_t fv; |
| |
| cap = cap_get_proc(); |
| if (!cap) |
| return -errno; |
| |
| if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0) |
| return -errno; |
| |
| return fv == CAP_SET; |
| } |
| |
| unsigned cap_last_cap(void) { |
| static thread_local unsigned saved; |
| static thread_local bool valid = false; |
| _cleanup_free_ char *content = NULL; |
| unsigned long p = 0; |
| int r; |
| |
| if (valid) |
| return saved; |
| |
| /* available since linux-3.2 */ |
| r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content); |
| if (r >= 0) { |
| r = safe_atolu(content, &p); |
| if (r >= 0) { |
| |
| if (p > 63) /* Safety for the future: if one day the kernel learns more than 64 caps, |
| * then we are in trouble (since we, as much userspace and kernel space |
| * store capability masks in uint64_t types). Let's hence protect |
| * ourselves against that and always cap at 63 for now. */ |
| p = 63; |
| |
| saved = p; |
| valid = true; |
| return p; |
| } |
| } |
| |
| /* fall back to syscall-probing for pre linux-3.2 */ |
| p = MIN((unsigned long) CAP_LAST_CAP, 63U); |
| |
| if (prctl(PR_CAPBSET_READ, p) < 0) { |
| |
| /* Hmm, look downwards, until we find one that works */ |
| for (p--; p > 0; p--) |
| if (prctl(PR_CAPBSET_READ, p) >= 0) |
| break; |
| |
| } else { |
| |
| /* Hmm, look upwards, until we find one that doesn't work */ |
| for (; p < 63; p++) |
| if (prctl(PR_CAPBSET_READ, p+1) < 0) |
| break; |
| } |
| |
| saved = p; |
| valid = true; |
| |
| return p; |
| } |
| |
| int capability_update_inherited_set(cap_t caps, uint64_t set) { |
| /* Add capabilities in the set to the inherited caps, drops capabilities not in the set. |
| * Do not apply them yet. */ |
| |
| for (unsigned i = 0; i <= cap_last_cap(); i++) { |
| cap_flag_value_t flag = set & (UINT64_C(1) << i) ? CAP_SET : CAP_CLEAR; |
| cap_value_t v; |
| |
| v = (cap_value_t) i; |
| |
| if (cap_set_flag(caps, CAP_INHERITABLE, 1, &v, flag) < 0) |
| return -errno; |
| } |
| |
| return 0; |
| } |
| |
| int capability_ambient_set_apply(uint64_t set, bool also_inherit) { |
| _cleanup_cap_free_ cap_t caps = NULL; |
| int r; |
| |
| /* Remove capabilities requested in ambient set, but not in the bounding set */ |
| for (unsigned i = 0; i <= cap_last_cap(); i++) { |
| if (set == 0) |
| break; |
| |
| if (FLAGS_SET(set, (UINT64_C(1) << i)) && prctl(PR_CAPBSET_READ, i) != 1) { |
| log_debug("Ambient capability %s requested but missing from bounding set," |
| " suppressing automatically.", capability_to_name(i)); |
| set &= ~(UINT64_C(1) << i); |
| } |
| } |
| |
| /* Add the capabilities to the ambient set (an possibly also the inheritable set) */ |
| |
| /* Check that we can use PR_CAP_AMBIENT or quit early. */ |
| if (!ambient_capabilities_supported()) |
| return (set & all_capabilities()) == 0 ? |
| 0 : -EOPNOTSUPP; /* if actually no ambient caps are to be set, be silent, |
| * otherwise fail recognizably */ |
| |
| if (also_inherit) { |
| caps = cap_get_proc(); |
| if (!caps) |
| return -errno; |
| |
| r = capability_update_inherited_set(caps, set); |
| if (r < 0) |
| return -errno; |
| |
| if (cap_set_proc(caps) < 0) |
| return -errno; |
| } |
| |
| for (unsigned i = 0; i <= cap_last_cap(); i++) { |
| |
| if (set & (UINT64_C(1) << i)) { |
| |
| /* Add the capability to the ambient set. */ |
| if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) < 0) |
| return -errno; |
| } else { |
| |
| /* Drop the capability so we don't inherit capabilities we didn't ask for. */ |
| r = prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, i, 0, 0); |
| if (r < 0) |
| return -errno; |
| |
| if (r) |
| if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_LOWER, i, 0, 0) < 0) |
| return -errno; |
| |
| } |
| } |
| |
| return 0; |
| } |
| |
| int capability_gain_cap_setpcap(cap_t *ret_before_caps) { |
| _cleanup_cap_free_ cap_t caps = NULL; |
| cap_flag_value_t fv; |
| caps = cap_get_proc(); |
| if (!caps) |
| return -errno; |
| |
| if (cap_get_flag(caps, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0) |
| return -errno; |
| |
| if (fv != CAP_SET) { |
| _cleanup_cap_free_ cap_t temp_cap = NULL; |
| static const cap_value_t v = CAP_SETPCAP; |
| |
| temp_cap = cap_dup(caps); |
| if (!temp_cap) |
| return -errno; |
| |
| if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) |
| return -errno; |
| |
| if (cap_set_proc(temp_cap) < 0) |
| log_debug_errno(errno, "Can't acquire effective CAP_SETPCAP bit, ignoring: %m"); |
| |
| /* If we didn't manage to acquire the CAP_SETPCAP bit, we continue anyway, after all this just means |
| * we'll fail later, when we actually intend to drop some capabilities or try to set securebits. */ |
| } |
| if (ret_before_caps) |
| /* Return the capabilities as they have been before setting CAP_SETPCAP */ |
| *ret_before_caps = TAKE_PTR(caps); |
| |
| return 0; |
| } |
| |
| int capability_bounding_set_drop(uint64_t keep, bool right_now) { |
| _cleanup_cap_free_ cap_t before_cap = NULL, after_cap = NULL; |
| int r; |
| |
| /* If we are run as PID 1 we will lack CAP_SETPCAP by default |
| * in the effective set (yes, the kernel drops that when |
| * executing init!), so get it back temporarily so that we can |
| * call PR_CAPBSET_DROP. */ |
| |
| r = capability_gain_cap_setpcap(&before_cap); |
| if (r < 0) |
| return r; |
| |
| after_cap = cap_dup(before_cap); |
| if (!after_cap) |
| return -errno; |
| |
| for (unsigned i = 0; i <= cap_last_cap(); i++) { |
| cap_value_t v; |
| |
| if ((keep & (UINT64_C(1) << i))) |
| continue; |
| |
| /* Drop it from the bounding set */ |
| if (prctl(PR_CAPBSET_DROP, i) < 0) { |
| r = -errno; |
| |
| /* If dropping the capability failed, let's see if we didn't have it in the first place. If so, |
| * continue anyway, as dropping a capability we didn't have in the first place doesn't really |
| * matter anyway. */ |
| if (prctl(PR_CAPBSET_READ, i) != 0) |
| goto finish; |
| } |
| v = (cap_value_t) i; |
| |
| /* Also drop it from the inheritable set, so |
| * that anything we exec() loses the |
| * capability for good. */ |
| if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) { |
| r = -errno; |
| goto finish; |
| } |
| |
| /* If we shall apply this right now drop it |
| * also from our own capability sets. */ |
| if (right_now) { |
| if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 || |
| cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) { |
| r = -errno; |
| goto finish; |
| } |
| } |
| } |
| |
| r = 0; |
| |
| finish: |
| if (cap_set_proc(after_cap) < 0) { |
| /* If there are no actual changes anyway then let's ignore this error. */ |
| if (cap_compare(before_cap, after_cap) != 0) |
| r = -errno; |
| } |
| |
| return r; |
| } |
| |
| static int drop_from_file(const char *fn, uint64_t keep) { |
| _cleanup_free_ char *p = NULL; |
| uint64_t current, after; |
| uint32_t hi, lo; |
| int r, k; |
| |
| r = read_one_line_file(fn, &p); |
| if (r < 0) |
| return r; |
| |
| k = sscanf(p, "%" PRIu32 " %" PRIu32, &lo, &hi); |
| if (k != 2) |
| return -EIO; |
| |
| current = (uint64_t) lo | ((uint64_t) hi << 32); |
| after = current & keep; |
| |
| if (current == after) |
| return 0; |
| |
| lo = after & UINT32_C(0xFFFFFFFF); |
| hi = (after >> 32) & UINT32_C(0xFFFFFFFF); |
| |
| return write_string_filef(fn, 0, "%" PRIu32 " %" PRIu32, lo, hi); |
| } |
| |
| int capability_bounding_set_drop_usermode(uint64_t keep) { |
| int r; |
| |
| r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", keep); |
| if (r < 0) |
| return r; |
| |
| r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", keep); |
| if (r < 0) |
| return r; |
| |
| return r; |
| } |
| |
| int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) { |
| int r; |
| |
| /* Unfortunately we cannot leave privilege dropping to PID 1 here, since we want to run as user but |
| * want to keep some capabilities. Since file capabilities have been introduced this cannot be done |
| * across exec() anymore, unless our binary has the capability configured in the file system, which |
| * we want to avoid. */ |
| |
| if (setresgid(gid, gid, gid) < 0) |
| return log_error_errno(errno, "Failed to change group ID: %m"); |
| |
| r = maybe_setgroups(0, NULL); |
| if (r < 0) |
| return log_error_errno(r, "Failed to drop auxiliary groups list: %m"); |
| |
| /* Ensure we keep the permitted caps across the setresuid(). Note that we do this even if we actually |
| * don't want to keep any capabilities, since we want to be able to drop them from the bounding set |
| * too, and we can only do that if we have capabilities. */ |
| if (prctl(PR_SET_KEEPCAPS, 1) < 0) |
| return log_error_errno(errno, "Failed to enable keep capabilities flag: %m"); |
| |
| if (setresuid(uid, uid, uid) < 0) |
| return log_error_errno(errno, "Failed to change user ID: %m"); |
| |
| if (prctl(PR_SET_KEEPCAPS, 0) < 0) |
| return log_error_errno(errno, "Failed to disable keep capabilities flag: %m"); |
| |
| /* Drop all caps from the bounding set (as well as the inheritable/permitted/effective sets), except |
| * the ones we want to keep */ |
| r = capability_bounding_set_drop(keep_capabilities, true); |
| if (r < 0) |
| return log_error_errno(r, "Failed to drop capabilities: %m"); |
| |
| /* Now upgrade the permitted caps we still kept to effective caps */ |
| if (keep_capabilities != 0) { |
| cap_value_t bits[log2u64(keep_capabilities) + 1]; |
| _cleanup_cap_free_ cap_t d = NULL; |
| unsigned i, j = 0; |
| |
| d = cap_init(); |
| if (!d) |
| return log_oom(); |
| |
| for (i = 0; i < ELEMENTSOF(bits); i++) |
| if (keep_capabilities & (1ULL << i)) |
| bits[j++] = i; |
| |
| /* use enough bits */ |
| assert(i == 64 || (keep_capabilities >> i) == 0); |
| /* don't use too many bits */ |
| assert(keep_capabilities & (UINT64_C(1) << (i - 1))); |
| |
| if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 || |
| cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0) |
| return log_error_errno(errno, "Failed to enable capabilities bits: %m"); |
| |
| if (cap_set_proc(d) < 0) |
| return log_error_errno(errno, "Failed to increase capabilities: %m"); |
| } |
| |
| return 0; |
| } |
| |
| int drop_capability(cap_value_t cv) { |
| _cleanup_cap_free_ cap_t tmp_cap = NULL; |
| |
| tmp_cap = cap_get_proc(); |
| if (!tmp_cap) |
| return -errno; |
| |
| if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, CAP_CLEAR) < 0) || |
| (cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) || |
| (cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0)) |
| return -errno; |
| |
| if (cap_set_proc(tmp_cap) < 0) |
| return -errno; |
| |
| return 0; |
| } |
| |
| bool ambient_capabilities_supported(void) { |
| static int cache = -1; |
| |
| if (cache >= 0) |
| return cache; |
| |
| /* If PR_CAP_AMBIENT returns something valid, or an unexpected error code we assume that ambient caps are |
| * available. */ |
| |
| cache = prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_KILL, 0, 0) >= 0 || |
| !IN_SET(errno, EINVAL, EOPNOTSUPP, ENOSYS); |
| |
| return cache; |
| } |
| |
| bool capability_quintet_mangle(CapabilityQuintet *q) { |
| uint64_t combined, drop = 0; |
| bool ambient_supported; |
| |
| assert(q); |
| |
| combined = q->effective | q->bounding | q->inheritable | q->permitted; |
| |
| ambient_supported = q->ambient != UINT64_MAX; |
| if (ambient_supported) |
| combined |= q->ambient; |
| |
| for (unsigned i = 0; i <= cap_last_cap(); i++) { |
| unsigned long bit = UINT64_C(1) << i; |
| if (!FLAGS_SET(combined, bit)) |
| continue; |
| |
| if (prctl(PR_CAPBSET_READ, i) > 0) |
| continue; |
| |
| drop |= bit; |
| |
| log_debug("Not in the current bounding set: %s", capability_to_name(i)); |
| } |
| |
| q->effective &= ~drop; |
| q->bounding &= ~drop; |
| q->inheritable &= ~drop; |
| q->permitted &= ~drop; |
| |
| if (ambient_supported) |
| q->ambient &= ~drop; |
| |
| return drop != 0; /* Let the caller know we changed something */ |
| } |
| |
| int capability_quintet_enforce(const CapabilityQuintet *q) { |
| _cleanup_cap_free_ cap_t c = NULL, modified = NULL; |
| int r; |
| |
| if (q->ambient != UINT64_MAX) { |
| bool changed = false; |
| |
| c = cap_get_proc(); |
| if (!c) |
| return -errno; |
| |
| /* In order to raise the ambient caps set we first need to raise the matching |
| * inheritable + permitted cap */ |
| for (unsigned i = 0; i <= cap_last_cap(); i++) { |
| uint64_t m = UINT64_C(1) << i; |
| cap_value_t cv = (cap_value_t) i; |
| cap_flag_value_t old_value_inheritable, old_value_permitted; |
| |
| if ((q->ambient & m) == 0) |
| continue; |
| |
| if (cap_get_flag(c, cv, CAP_INHERITABLE, &old_value_inheritable) < 0) |
| return -errno; |
| if (cap_get_flag(c, cv, CAP_PERMITTED, &old_value_permitted) < 0) |
| return -errno; |
| |
| if (old_value_inheritable == CAP_SET && old_value_permitted == CAP_SET) |
| continue; |
| |
| if (cap_set_flag(c, CAP_INHERITABLE, 1, &cv, CAP_SET) < 0) |
| return -errno; |
| if (cap_set_flag(c, CAP_PERMITTED, 1, &cv, CAP_SET) < 0) |
| return -errno; |
| |
| changed = true; |
| } |
| |
| if (changed) |
| if (cap_set_proc(c) < 0) |
| return -errno; |
| |
| r = capability_ambient_set_apply(q->ambient, false); |
| if (r < 0) |
| return r; |
| } |
| |
| if (q->inheritable != UINT64_MAX || q->permitted != UINT64_MAX || q->effective != UINT64_MAX) { |
| bool changed = false; |
| |
| if (!c) { |
| c = cap_get_proc(); |
| if (!c) |
| return -errno; |
| } |
| |
| for (unsigned i = 0; i <= cap_last_cap(); i++) { |
| uint64_t m = UINT64_C(1) << i; |
| cap_value_t cv = (cap_value_t) i; |
| |
| if (q->inheritable != UINT64_MAX) { |
| cap_flag_value_t old_value, new_value; |
| |
| if (cap_get_flag(c, cv, CAP_INHERITABLE, &old_value) < 0) { |
| if (errno == EINVAL) /* If the kernel knows more caps than this |
| * version of libcap, then this will return |
| * EINVAL. In that case, simply ignore it, |
| * pretend it doesn't exist. */ |
| continue; |
| |
| return -errno; |
| } |
| |
| new_value = (q->inheritable & m) ? CAP_SET : CAP_CLEAR; |
| |
| if (old_value != new_value) { |
| changed = true; |
| |
| if (cap_set_flag(c, CAP_INHERITABLE, 1, &cv, new_value) < 0) |
| return -errno; |
| } |
| } |
| |
| if (q->permitted != UINT64_MAX) { |
| cap_flag_value_t old_value, new_value; |
| |
| if (cap_get_flag(c, cv, CAP_PERMITTED, &old_value) < 0) { |
| if (errno == EINVAL) |
| continue; |
| |
| return -errno; |
| } |
| |
| new_value = (q->permitted & m) ? CAP_SET : CAP_CLEAR; |
| |
| if (old_value != new_value) { |
| changed = true; |
| |
| if (cap_set_flag(c, CAP_PERMITTED, 1, &cv, new_value) < 0) |
| return -errno; |
| } |
| } |
| |
| if (q->effective != UINT64_MAX) { |
| cap_flag_value_t old_value, new_value; |
| |
| if (cap_get_flag(c, cv, CAP_EFFECTIVE, &old_value) < 0) { |
| if (errno == EINVAL) |
| continue; |
| |
| return -errno; |
| } |
| |
| new_value = (q->effective & m) ? CAP_SET : CAP_CLEAR; |
| |
| if (old_value != new_value) { |
| changed = true; |
| |
| if (cap_set_flag(c, CAP_EFFECTIVE, 1, &cv, new_value) < 0) |
| return -errno; |
| } |
| } |
| } |
| |
| if (changed) { |
| /* In order to change the bounding caps, we need to keep CAP_SETPCAP for a bit |
| * longer. Let's add it to our list hence for now. */ |
| if (q->bounding != UINT64_MAX) { |
| cap_value_t cv = CAP_SETPCAP; |
| |
| modified = cap_dup(c); |
| if (!modified) |
| return -ENOMEM; |
| |
| if (cap_set_flag(modified, CAP_PERMITTED, 1, &cv, CAP_SET) < 0) |
| return -errno; |
| if (cap_set_flag(modified, CAP_EFFECTIVE, 1, &cv, CAP_SET) < 0) |
| return -errno; |
| |
| if (cap_compare(modified, c) == 0) { |
| /* No change? then drop this nonsense again */ |
| cap_free(modified); |
| modified = NULL; |
| } |
| } |
| |
| /* Now, let's enforce the caps for the first time. Note that this is where we acquire |
| * caps in any of the sets we currently don't have. We have to do this before |
| * dropping the bounding caps below, since at that point we can never acquire new |
| * caps in inherited/permitted/effective anymore, but only lose them. */ |
| if (cap_set_proc(modified ?: c) < 0) |
| return -errno; |
| } |
| } |
| |
| if (q->bounding != UINT64_MAX) { |
| r = capability_bounding_set_drop(q->bounding, false); |
| if (r < 0) |
| return r; |
| } |
| |
| /* If needed, let's now set the caps again, this time in the final version, which differs from what |
| * we have already set only in the CAP_SETPCAP bit, which we needed for dropping the bounding |
| * bits. This call only undoes bits and doesn't acquire any which means the bounding caps don't |
| * matter. */ |
| if (modified) |
| if (cap_set_proc(c) < 0) |
| return -errno; |
| |
| return 0; |
| } |
