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-rw-r--r--src/core/selinux-access.c271
1 files changed, 271 insertions, 0 deletions
diff --git a/src/core/selinux-access.c b/src/core/selinux-access.c
new file mode 100644
index 0000000..0c6d885
--- /dev/null
+++ b/src/core/selinux-access.c
@@ -0,0 +1,271 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include "selinux-access.h"
+
+#if HAVE_SELINUX
+
+#include <errno.h>
+#include <selinux/avc.h>
+#include <selinux/selinux.h>
+#include <stdio.h>
+#if HAVE_AUDIT
+#include <libaudit.h>
+#endif
+
+#include "sd-bus.h"
+
+#include "alloc-util.h"
+#include "audit-fd.h"
+#include "bus-util.h"
+#include "log.h"
+#include "path-util.h"
+#include "selinux-util.h"
+#include "stdio-util.h"
+#include "strv.h"
+#include "util.h"
+
+static bool initialized = false;
+
+struct audit_info {
+ sd_bus_creds *creds;
+ const char *path;
+ const char *cmdline;
+};
+
+/*
+ Any time an access gets denied this callback will be called
+ with the audit data. We then need to just copy the audit data into the msgbuf.
+*/
+static int audit_callback(
+ void *auditdata,
+ security_class_t cls,
+ char *msgbuf,
+ size_t msgbufsize) {
+
+ const struct audit_info *audit = auditdata;
+ uid_t uid = 0, login_uid = 0;
+ gid_t gid = 0;
+ char login_uid_buf[DECIMAL_STR_MAX(uid_t) + 1] = "n/a";
+ char uid_buf[DECIMAL_STR_MAX(uid_t) + 1] = "n/a";
+ char gid_buf[DECIMAL_STR_MAX(gid_t) + 1] = "n/a";
+
+ if (sd_bus_creds_get_audit_login_uid(audit->creds, &login_uid) >= 0)
+ xsprintf(login_uid_buf, UID_FMT, login_uid);
+ if (sd_bus_creds_get_euid(audit->creds, &uid) >= 0)
+ xsprintf(uid_buf, UID_FMT, uid);
+ if (sd_bus_creds_get_egid(audit->creds, &gid) >= 0)
+ xsprintf(gid_buf, GID_FMT, gid);
+
+ snprintf(msgbuf, msgbufsize,
+ "auid=%s uid=%s gid=%s%s%s%s%s%s%s",
+ login_uid_buf, uid_buf, gid_buf,
+ audit->path ? " path=\"" : "", strempty(audit->path), audit->path ? "\"" : "",
+ audit->cmdline ? " cmdline=\"" : "", strempty(audit->cmdline), audit->cmdline ? "\"" : "");
+
+ return 0;
+}
+
+static int callback_type_to_priority(int type) {
+ switch(type) {
+
+ case SELINUX_ERROR:
+ return LOG_ERR;
+
+ case SELINUX_WARNING:
+ return LOG_WARNING;
+
+ case SELINUX_INFO:
+ return LOG_INFO;
+
+ case SELINUX_AVC:
+ default:
+ return LOG_NOTICE;
+ }
+}
+
+/*
+ libselinux uses this callback when access gets denied or other
+ events happen. If audit is turned on, messages will be reported
+ using audit netlink, otherwise they will be logged using the usual
+ channels.
+
+ Code copied from dbus and modified.
+*/
+_printf_(2, 3) static int log_callback(int type, const char *fmt, ...) {
+ va_list ap;
+ const char *fmt2;
+
+#if HAVE_AUDIT
+ int fd;
+
+ fd = get_audit_fd();
+
+ if (fd >= 0) {
+ _cleanup_free_ char *buf = NULL;
+ int r;
+
+ va_start(ap, fmt);
+ r = vasprintf(&buf, fmt, ap);
+ va_end(ap);
+
+ if (r >= 0) {
+ audit_log_user_avc_message(fd, AUDIT_USER_AVC, buf, NULL, NULL, NULL, 0);
+ return 0;
+ }
+ }
+#endif
+
+ fmt2 = strjoina("selinux: ", fmt);
+
+ va_start(ap, fmt);
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wformat-nonliteral"
+ log_internalv(LOG_AUTH | callback_type_to_priority(type),
+ 0, __FILE__, __LINE__, __FUNCTION__,
+ fmt2, ap);
+#pragma GCC diagnostic pop
+ va_end(ap);
+
+ return 0;
+}
+
+static int access_init(sd_bus_error *error) {
+
+ if (!mac_selinux_use())
+ return 0;
+
+ if (initialized)
+ return 1;
+
+ if (avc_open(NULL, 0) != 0) {
+ int enforce, saved_errno = errno;
+
+ enforce = security_getenforce();
+ log_full_errno(enforce != 0 ? LOG_ERR : LOG_WARNING, saved_errno, "Failed to open the SELinux AVC: %m");
+
+ /* If enforcement isn't on, then let's suppress this
+ * error, and just don't do any AVC checks. The
+ * warning we printed is hence all the admin will
+ * see. */
+ if (enforce == 0)
+ return 0;
+
+ /* Return an access denied error, if we couldn't load
+ * the AVC but enforcing mode was on, or we couldn't
+ * determine whether it is one. */
+ return sd_bus_error_setf(error, SD_BUS_ERROR_ACCESS_DENIED, "Failed to open the SELinux AVC: %s", strerror(saved_errno));
+ }
+
+ selinux_set_callback(SELINUX_CB_AUDIT, (union selinux_callback) audit_callback);
+ selinux_set_callback(SELINUX_CB_LOG, (union selinux_callback) log_callback);
+
+ initialized = true;
+ return 1;
+}
+
+/*
+ This function communicates with the kernel to check whether or not it should
+ allow the access.
+ If the machine is in permissive mode it will return ok. Audit messages will
+ still be generated if the access would be denied in enforcing mode.
+*/
+int mac_selinux_generic_access_check(
+ sd_bus_message *message,
+ const char *path,
+ const char *permission,
+ sd_bus_error *error) {
+
+ _cleanup_(sd_bus_creds_unrefp) sd_bus_creds *creds = NULL;
+ const char *tclass = NULL, *scon = NULL;
+ struct audit_info audit_info = {};
+ _cleanup_free_ char *cl = NULL;
+ char *fcon = NULL;
+ char **cmdline = NULL;
+ int r = 0;
+
+ assert(message);
+ assert(permission);
+ assert(error);
+
+ r = access_init(error);
+ if (r <= 0)
+ return r;
+
+ r = sd_bus_query_sender_creds(
+ message,
+ SD_BUS_CREDS_PID|SD_BUS_CREDS_EUID|SD_BUS_CREDS_EGID|
+ SD_BUS_CREDS_CMDLINE|SD_BUS_CREDS_AUDIT_LOGIN_UID|
+ SD_BUS_CREDS_SELINUX_CONTEXT|
+ SD_BUS_CREDS_AUGMENT /* get more bits from /proc */,
+ &creds);
+ if (r < 0)
+ goto finish;
+
+ /* The SELinux context is something we really should have
+ * gotten directly from the message or sender, and not be an
+ * augmented field. If it was augmented we cannot use it for
+ * authorization, since this is racy and vulnerable. Let's add
+ * an extra check, just in case, even though this really
+ * shouldn't be possible. */
+ assert_return((sd_bus_creds_get_augmented_mask(creds) & SD_BUS_CREDS_SELINUX_CONTEXT) == 0, -EPERM);
+
+ r = sd_bus_creds_get_selinux_context(creds, &scon);
+ if (r < 0)
+ goto finish;
+
+ if (path) {
+ /* Get the file context of the unit file */
+
+ r = getfilecon_raw(path, &fcon);
+ if (r < 0) {
+ r = sd_bus_error_setf(error, SD_BUS_ERROR_ACCESS_DENIED, "Failed to get file context on %s.", path);
+ goto finish;
+ }
+
+ tclass = "service";
+ } else {
+ r = getcon_raw(&fcon);
+ if (r < 0) {
+ r = sd_bus_error_setf(error, SD_BUS_ERROR_ACCESS_DENIED, "Failed to get current context.");
+ goto finish;
+ }
+
+ tclass = "system";
+ }
+
+ sd_bus_creds_get_cmdline(creds, &cmdline);
+ cl = strv_join(cmdline, " ");
+
+ audit_info.creds = creds;
+ audit_info.path = path;
+ audit_info.cmdline = cl;
+
+ r = selinux_check_access(scon, fcon, tclass, permission, &audit_info);
+ if (r < 0)
+ r = sd_bus_error_setf(error, SD_BUS_ERROR_ACCESS_DENIED, "SELinux policy denies access.");
+
+ log_debug("SELinux access check scon=%s tcon=%s tclass=%s perm=%s path=%s cmdline=%s: %i", scon, fcon, tclass, permission, path, cl, r);
+
+finish:
+ freecon(fcon);
+
+ if (r < 0 && security_getenforce() != 1) {
+ sd_bus_error_free(error);
+ r = 0;
+ }
+
+ return r;
+}
+
+#else
+
+int mac_selinux_generic_access_check(
+ sd_bus_message *message,
+ const char *path,
+ const char *permission,
+ sd_bus_error *error) {
+
+ return 0;
+}
+
+#endif
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-16 12:48:35 +0000