Nick Rosbrook
362235bf59
If a container manager does not follow the guidance in https://systemd.io/CONTAINER_INTERFACE/ regarding audit capabilities, then the current check may not be sufficient to determine that audit will function properly. In particular, when calling bind() on the audit fd, we will get EPERM if running in a user-namespaced container. Expand the check to make an AUDIT_GET_FEATURE request on the audit fd to test if it is working. If this fails with ECONNREFUSED, we know it is because the kernel does not support the use of audit outside of the initial user namespace. Note that the approach of this patch was suggested here: https://github.com/systemd/systemd/pull/19443#issuecomment-829566659 Fixes: #6519
149 lines
4.2 KiB
C
149 lines
4.2 KiB
C
/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#include <errno.h>
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#include <linux/audit.h>
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#include <linux/netlink.h>
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#include <stdio.h>
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#include <sys/socket.h>
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#include "alloc-util.h"
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#include "audit-util.h"
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#include "fd-util.h"
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#include "fileio.h"
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#include "macro.h"
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#include "parse-util.h"
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#include "process-util.h"
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#include "socket-util.h"
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#include "user-util.h"
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int audit_session_from_pid(pid_t pid, uint32_t *id) {
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_cleanup_free_ char *s = NULL;
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const char *p;
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uint32_t u;
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int r;
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assert(id);
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/* We don't convert ENOENT to ESRCH here, since we can't
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* really distinguish between "audit is not available in the
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* kernel" and "the process does not exist", both which will
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* result in ENOENT. */
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p = procfs_file_alloca(pid, "sessionid");
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r = read_one_line_file(p, &s);
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if (r < 0)
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return r;
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r = safe_atou32(s, &u);
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if (r < 0)
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return r;
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if (!audit_session_is_valid(u))
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return -ENODATA;
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*id = u;
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return 0;
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}
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int audit_loginuid_from_pid(pid_t pid, uid_t *uid) {
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_cleanup_free_ char *s = NULL;
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const char *p;
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uid_t u;
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int r;
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assert(uid);
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p = procfs_file_alloca(pid, "loginuid");
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r = read_one_line_file(p, &s);
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if (r < 0)
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return r;
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r = parse_uid(s, &u);
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if (r == -ENXIO) /* the UID was -1 */
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return -ENODATA;
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if (r < 0)
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return r;
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*uid = u;
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return 0;
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}
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static int try_audit_request(int fd) {
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struct iovec iov;
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struct msghdr mh;
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ssize_t n;
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assert(fd >= 0);
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struct {
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struct nlmsghdr hdr;
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struct nlmsgerr err;
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} _packed_ msg = {
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.hdr.nlmsg_len = NLMSG_LENGTH(0),
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.hdr.nlmsg_type = AUDIT_GET_FEATURE,
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.hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK,
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};
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iov = (struct iovec) {
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.iov_base = &msg,
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.iov_len = msg.hdr.nlmsg_len,
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};
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mh = (struct msghdr) {
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.msg_iov = &iov,
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.msg_iovlen = 1,
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};
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if (sendmsg(fd, &mh, MSG_NOSIGNAL) < 0)
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return -errno;
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iov.iov_len = sizeof(msg);
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n = recvmsg_safe(fd, &mh, 0);
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if (n < 0)
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return -errno;
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if (n != NLMSG_LENGTH(sizeof(struct nlmsgerr)))
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return -EIO;
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if (msg.hdr.nlmsg_type != NLMSG_ERROR)
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return -EINVAL;
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return msg.err.error;
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}
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bool use_audit(void) {
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static int cached_use = -1;
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int r;
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if (cached_use < 0) {
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int fd;
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fd = socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC|SOCK_NONBLOCK, NETLINK_AUDIT);
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if (fd < 0) {
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cached_use = !IN_SET(errno, EAFNOSUPPORT, EPROTONOSUPPORT, EPERM);
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if (!cached_use)
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log_debug_errno(errno, "Won't talk to audit: %m");
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} else {
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/* If we try and use the audit fd but get -ECONNREFUSED, it is because
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* we are not in the initial user namespace, and the kernel does not
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* have support for audit outside of the initial user namespace
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* (see https://elixir.bootlin.com/linux/latest/C/ident/audit_netlink_ok).
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*
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* If we receive any other error, do not disable audit because we are not
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* sure that the error indicates that audit will not work in general. */
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r = try_audit_request(fd);
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if (r < 0) {
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cached_use = r != -ECONNREFUSED;
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log_debug_errno(r, cached_use ?
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"Failed to make request on audit fd, ignoring: %m" :
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"Won't talk to audit: %m");
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} else
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cached_use = true;
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safe_close(fd);
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}
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}
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return cached_use;
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}
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