src/basic/audit-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <errno.h>
   4 #include <linux/audit.h>
   5 #include <linux/netlink.h>
   6 #include <stdio.h>
   7 #include <sys/socket.h>
   8
   9 #include "alloc-util.h"
  10 #include "audit-util.h"
  11 #include "fd-util.h"
  12 #include "fileio.h"
  13 #include "iovec-util.h"
  14 #include "macro.h"
  15 #include "parse-util.h"
  16 #include "process-util.h"
  17 #include "socket-util.h"
  18 #include "user-util.h"
  19
  20 int audit_session_from_pid(pid_t pid, uint32_t *id) {
  21         _cleanup_free_ char *s = NULL;
  22         const char *p;
  23         uint32_t u;
  24         int r;
  25
  26         assert(id);
  27
  28         /* We don't convert ENOENT to ESRCH here, since we can't
  29          * really distinguish between "audit is not available in the
  30          * kernel" and "the process does not exist", both which will
  31          * result in ENOENT. */
  32
  33         p = procfs_file_alloca(pid, "sessionid");
  34
  35         r = read_one_line_file(p, &s);
  36         if (r < 0)
  37                 return r;
  38
  39         r = safe_atou32(s, &u);
  40         if (r < 0)
  41                 return r;
  42
  43         if (!audit_session_is_valid(u))
  44                 return -ENODATA;
  45
  46         *id = u;
  47         return 0;
  48 }
  49
  50 int audit_loginuid_from_pid(pid_t pid, uid_t *uid) {
  51         _cleanup_free_ char *s = NULL;
  52         const char *p;
  53         uid_t u;
  54         int r;
  55
  56         assert(uid);
  57
  58         p = procfs_file_alloca(pid, "loginuid");
  59
  60         r = read_one_line_file(p, &s);
  61         if (r < 0)
  62                 return r;
  63
  64         r = parse_uid(s, &u);
  65         if (r == -ENXIO) /* the UID was -1 */
  66                 return -ENODATA;
  67         if (r < 0)
  68                 return r;
  69
  70         *uid = u;
  71         return 0;
  72 }
  73
  74 static int try_audit_request(int fd) {
  75         struct iovec iov;
  76         struct msghdr mh;
  77         ssize_t n;
  78
  79         assert(fd >= 0);
  80
  81         struct {
  82                 struct nlmsghdr hdr;
  83                 struct nlmsgerr err;
  84         } _packed_ msg = {
  85                 .hdr.nlmsg_len = NLMSG_LENGTH(0),
  86                 .hdr.nlmsg_type = AUDIT_GET_FEATURE,
  87                 .hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK,
  88         };
  89         iov = IOVEC_MAKE(&msg, msg.hdr.nlmsg_len);
  90         mh = (struct msghdr) {
  91                 .msg_iov = &iov,
  92                 .msg_iovlen = 1,
  93         };
  94
  95         if (sendmsg(fd, &mh, MSG_NOSIGNAL) < 0)
  96                 return -errno;
  97
  98         iov.iov_len = sizeof(msg);
  99
 100         n = recvmsg_safe(fd, &mh, 0);
 101         if (n < 0)
 102                 return n;
 103         if (n != NLMSG_LENGTH(sizeof(struct nlmsgerr)))
 104                 return -EIO;
 105
 106         if (msg.hdr.nlmsg_type != NLMSG_ERROR)
 107                 return -EINVAL;
 108
 109         return msg.err.error;
 110 }
 111
 112 bool use_audit(void) {
 113         static int cached_use = -1;
 114         int r;
 115
 116         if (cached_use < 0) {
 117                 int fd;
 118
 119                 fd = socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC|SOCK_NONBLOCK, NETLINK_AUDIT);
 120                 if (fd < 0) {
 121                         cached_use = !IN_SET(errno, EAFNOSUPPORT, EPROTONOSUPPORT, EPERM);
 122                         if (!cached_use)
 123                                 log_debug_errno(errno, "Won't talk to audit: %m");
 124                 } else {
 125                         /* If we try and use the audit fd but get -ECONNREFUSED, it is because
 126                          * we are not in the initial user namespace, and the kernel does not
 127                          * have support for audit outside of the initial user namespace
 128                          * (see https://elixir.bootlin.com/linux/latest/C/ident/audit_netlink_ok).
 129                          *
 130                          * If we receive any other error, do not disable audit because we are not
 131                          * sure that the error indicates that audit will not work in general. */
 132                         r = try_audit_request(fd);
 133                         if (r < 0) {
 134                                 cached_use = r != -ECONNREFUSED;
 135                                 log_debug_errno(r, cached_use ?
 136                                                    "Failed to make request on audit fd, ignoring: %m" :
 137                                                    "Won't talk to audit: %m");
 138                         } else
 139                                 cached_use = true;
 140
 141                         safe_close(fd);
 142                 }
 143         }
 144
 145         return cached_use;
 146 }