1 files changed, 146 insertions, 0 deletions
diff --git a/src/basic/audit-util.c b/src/basic/audit-util.c
new file mode 100644
index 0000000..bf96e08
--- /dev/null
+++ b/src/basic/audit-util.c
@@ -0,0 +1,146 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <linux/audit.h>
+#include <linux/netlink.h>
+#include <stdio.h>
+#include <sys/socket.h>
+
+#include "alloc-util.h"
+#include "audit-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "iovec-util.h"
+#include "macro.h"
+#include "parse-util.h"
+#include "process-util.h"
+#include "socket-util.h"
+#include "user-util.h"
+
+int audit_session_from_pid(pid_t pid, uint32_t *id) {
+        _cleanup_free_ char *s = NULL;
+        const char *p;
+        uint32_t u;
+        int r;
+
+        assert(id);
+
+        /* We don't convert ENOENT to ESRCH here, since we can't
+         * really distinguish between "audit is not available in the
+         * kernel" and "the process does not exist", both which will
+         * result in ENOENT. */
+
+        p = procfs_file_alloca(pid, "sessionid");
+
+        r = read_one_line_file(p, &s);
+        if (r < 0)
+                return r;
+
+        r = safe_atou32(s, &u);
+        if (r < 0)
+                return r;
+
+        if (!audit_session_is_valid(u))
+                return -ENODATA;
+
+        *id = u;
+        return 0;
+}
+
+int audit_loginuid_from_pid(pid_t pid, uid_t *uid) {
+        _cleanup_free_ char *s = NULL;
+        const char *p;
+        uid_t u;
+        int r;
+
+        assert(uid);
+
+        p = procfs_file_alloca(pid, "loginuid");
+
+        r = read_one_line_file(p, &s);
+        if (r < 0)
+                return r;
+
+        r = parse_uid(s, &u);
+        if (r == -ENXIO) /* the UID was -1 */
+                return -ENODATA;
+        if (r < 0)
+                return r;
+
+        *uid = u;
+        return 0;
+}
+
+static int try_audit_request(int fd) {
+        struct iovec iov;
+        struct msghdr mh;
+        ssize_t n;
+
+        assert(fd >= 0);
+
+        struct {
+                struct nlmsghdr hdr;
+                struct nlmsgerr err;
+        } _packed_ msg = {
+                .hdr.nlmsg_len = NLMSG_LENGTH(0),
+                .hdr.nlmsg_type = AUDIT_GET_FEATURE,
+                .hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK,
+        };
+        iov = IOVEC_MAKE(&msg, msg.hdr.nlmsg_len);
+        mh = (struct msghdr) {
+                .msg_iov = &iov,
+                .msg_iovlen = 1,
+        };
+
+        if (sendmsg(fd, &mh, MSG_NOSIGNAL) < 0)
+                return -errno;
+
+        iov.iov_len = sizeof(msg);
+
+        n = recvmsg_safe(fd, &mh, 0);
+        if (n < 0)
+                return -errno;
+        if (n != NLMSG_LENGTH(sizeof(struct nlmsgerr)))
+                return -EIO;
+
+        if (msg.hdr.nlmsg_type != NLMSG_ERROR)
+                return -EINVAL;
+
+        return msg.err.error;
+}
+
+bool use_audit(void) {
+        static int cached_use = -1;
+        int r;
+
+        if (cached_use < 0) {
+                int fd;
+
+                fd = socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC|SOCK_NONBLOCK, NETLINK_AUDIT);
+                if (fd < 0) {
+                        cached_use = !IN_SET(errno, EAFNOSUPPORT, EPROTONOSUPPORT, EPERM);
+                        if (!cached_use)
+                                log_debug_errno(errno, "Won't talk to audit: %m");
+                } else {
+                        /* If we try and use the audit fd but get -ECONNREFUSED, it is because
+                         * we are not in the initial user namespace, and the kernel does not
+                         * have support for audit outside of the initial user namespace
+                         * (see https://elixir.bootlin.com/linux/latest/C/ident/audit_netlink_ok).
+                         *
+                         * If we receive any other error, do not disable audit because we are not
+                         * sure that the error indicates that audit will not work in general. */
+                        r = try_audit_request(fd);
+                        if (r < 0) {
+                                cached_use = r != -ECONNREFUSED;
+                                log_debug_errno(r, cached_use ?
+                                                   "Failed to make request on audit fd, ignoring: %m" :
+                                                   "Won't talk to audit: %m");
+                        } else
+                                cached_use = true;
+
+                        safe_close(fd);
+                }
+        }
+
+        return cached_use;
+}