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authorRichard Guy Briggs <rgb@redhat.com>2014-04-22 21:31:57 -0400
committerDavid S. Miller <davem@davemloft.net>2014-04-22 21:42:27 -0400
commit451f921639fea4600dfb9ab2889332bdcc7b48d3 (patch)
tree64077829e0b9634a9dfc33558b19df3ef682ed6a /kernel/audit.c
parent3a101b8de0d39403b2c7e5c23fd0b005668acf48 (diff)
downloadlinux-sh-451f921639fea4600dfb9ab2889332bdcc7b48d3.tar.gz
audit: add netlink multicast group for log read
Add a netlink multicast socket with one group to kaudit for "best-effort" delivery to read-only userspace clients such as systemd, in addition to the existing bidirectional unicast auditd userspace client. Currently, auditd is intended to use the CAP_AUDIT_CONTROL and CAP_AUDIT_WRITE capabilities, but actually uses CAP_NET_ADMIN. The CAP_AUDIT_READ capability is added for use by read-only AUDIT_NLGRP_READLOG netlink multicast group clients to the kaudit subsystem. This will safely give access to services such as systemd to consume audit logs while ensuring write access remains restricted for integrity. Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'kernel/audit.c')
-rw-r--r--kernel/audit.c51
1 files changed, 47 insertions, 4 deletions
diff --git a/kernel/audit.c b/kernel/audit.c
index 223cb746f141..d272cc11dff4 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -424,6 +424,35 @@ static void kauditd_send_skb(struct sk_buff *skb)
}
/*
+ * kauditd_send_multicast_skb - send the skb to multicast userspace listeners
+ *
+ * This function doesn't consume an skb as might be expected since it has to
+ * copy it anyways.
+ */
+static void kauditd_send_multicast_skb(struct sk_buff *skb)
+{
+ struct sk_buff *copy;
+ struct audit_net *aunet = net_generic(&init_net, audit_net_id);
+ struct sock *sock = aunet->nlsk;
+
+ /*
+ * The seemingly wasteful skb_copy() rather than bumping the refcount
+ * using skb_get() is necessary because non-standard mods are made to
+ * the skb by the original kaudit unicast socket send routine. The
+ * existing auditd daemon assumes this breakage. Fixing this would
+ * require co-ordinating a change in the established protocol between
+ * the kaudit kernel subsystem and the auditd userspace code. There is
+ * no reason for new multicast clients to continue with this
+ * non-compliance.
+ */
+ copy = skb_copy(skb, GFP_KERNEL);
+ if (!copy)
+ return;
+
+ nlmsg_multicast(sock, copy, 0, AUDIT_NLGRP_READLOG, GFP_KERNEL);
+}
+
+/*
* flush_hold_queue - empty the hold queue if auditd appears
*
* If auditd just started, drain the queue of messages already
@@ -1090,6 +1119,8 @@ static int __net_init audit_net_init(struct net *net)
struct netlink_kernel_cfg cfg = {
.input = audit_receive,
.bind = audit_bind,
+ .flags = NL_CFG_F_NONROOT_RECV,
+ .groups = AUDIT_NLGRP_MAX,
};
struct audit_net *aunet = net_generic(net, audit_net_id);
@@ -1911,10 +1942,10 @@ out:
* audit_log_end - end one audit record
* @ab: the audit_buffer
*
- * The netlink_* functions cannot be called inside an irq context, so
- * the audit buffer is placed on a queue and a tasklet is scheduled to
- * remove them from the queue outside the irq context. May be called in
- * any context.
+ * netlink_unicast() cannot be called inside an irq context because it blocks
+ * (last arg, flags, is not set to MSG_DONTWAIT), so the audit buffer is placed
+ * on a queue and a tasklet is scheduled to remove them from the queue outside
+ * the irq context. May be called in any context.
*/
void audit_log_end(struct audit_buffer *ab)
{
@@ -1924,6 +1955,18 @@ void audit_log_end(struct audit_buffer *ab)
audit_log_lost("rate limit exceeded");
} else {
struct nlmsghdr *nlh = nlmsg_hdr(ab->skb);
+
+ kauditd_send_multicast_skb(ab->skb);
+
+ /*
+ * The original kaudit unicast socket sends up messages with
+ * nlmsg_len set to the payload length rather than the entire
+ * message length. This breaks the standard set by netlink.
+ * The existing auditd daemon assumes this breakage. Fixing
+ * this would require co-ordinating a change in the established
+ * protocol between the kaudit kernel subsystem and the auditd
+ * userspace code.
+ */
nlh->nlmsg_len = ab->skb->len - NLMSG_HDRLEN;
if (audit_pid) {