Adding upstream version 252.22.upstream/252.22

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 607 insertions, 0 deletions

diff --git a/src/basic/capability-util.c b/src/basic/capability-util.c
new file mode 100644
index 0000000..c9c0b50
--- /dev/null
+++ b/src/basic/capability-util.c
@@ -0,0 +1,607 @@
+/* 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 "macro.h"
+#include "missing_prctl.h"
+#include "missing_threads.h"
+#include "parse-util.h"
+#include "user-util.h"
+#include "util.h"
+
+int have_effective_cap(int value) {
+        _cleanup_cap_free_ cap_t cap = NULL;
+        cap_flag_value_t fv = CAP_CLEAR; /* To avoid false-positive use-of-uninitialized-value error reported
+                                          * by fuzzers. */
+
+        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;
+}