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linux/security/lsm_audit.c
Richard Guy Briggs 5deeb5cece lsm: copy comm before calling audit_log to avoid race in string printing 
When task->comm is passed directly to audit_log_untrustedstring() without
getting a copy or using the task_lock, there is a race that could happen that
would output a NULL (\0) in the middle of the output string that would
effectively truncate the rest of the report text after the comm= field in the
audit log message, losing fields.

Using get_task_comm() to get a copy while acquiring the task_lock to prevent
this and to prevent the result from being a mixture of old and new values of
comm would incur potentially unacceptable overhead, considering that the value
can be influenced by userspace and therefore untrusted anyways.

Copy the value before passing it to audit_log_untrustedstring() ensures that a
local copy is used to calculate the length *and* subsequently printed.  Even if
this value contains a mix of old and new values, it will only calculate and
copy up to the first NULL, preventing the rest of the audit log message being
truncated.

Use a second local copy of comm to avoid a race between the first and second
calls to audit_log_untrustedstring() with comm.

Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
2015-04-15 10:13:20 +10:00

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/*
* common LSM auditing functions
*
* Based on code written for SELinux by :
* Stephen Smalley, <sds@epoch.ncsc.mil>
* James Morris <jmorris@redhat.com>
* Author : Etienne Basset, <etienne.basset@ensta.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2,
* as published by the Free Software Foundation.
*/
#include <linux/types.h>
#include <linux/stddef.h>
#include <linux/kernel.h>
#include <linux/gfp.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <net/sock.h>
#include <linux/un.h>
#include <net/af_unix.h>
#include <linux/audit.h>
#include <linux/ipv6.h>
#include <linux/ip.h>
#include <net/ip.h>
#include <net/ipv6.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/dccp.h>
#include <linux/sctp.h>
#include <linux/lsm_audit.h>
/**
* ipv4_skb_to_auditdata : fill auditdata from skb
* @skb : the skb
* @ad : the audit data to fill
* @proto : the layer 4 protocol
*
* return 0 on success
*/
int ipv4_skb_to_auditdata(struct sk_buff *skb,
struct common_audit_data *ad, u8 *proto)
{
int ret = 0;
struct iphdr *ih;
ih = ip_hdr(skb);
if (ih == NULL)
return -EINVAL;
ad->u.net->v4info.saddr = ih->saddr;
ad->u.net->v4info.daddr = ih->daddr;
if (proto)
*proto = ih->protocol;
/* non initial fragment */
if (ntohs(ih->frag_off) & IP_OFFSET)
return 0;
switch (ih->protocol) {
case IPPROTO_TCP: {
struct tcphdr *th = tcp_hdr(skb);
if (th == NULL)
break;
ad->u.net->sport = th->source;
ad->u.net->dport = th->dest;
break;
}
case IPPROTO_UDP: {
struct udphdr *uh = udp_hdr(skb);
if (uh == NULL)
break;
ad->u.net->sport = uh->source;
ad->u.net->dport = uh->dest;
break;
}
case IPPROTO_DCCP: {
struct dccp_hdr *dh = dccp_hdr(skb);
if (dh == NULL)
break;
ad->u.net->sport = dh->dccph_sport;
ad->u.net->dport = dh->dccph_dport;
break;
}
case IPPROTO_SCTP: {
struct sctphdr *sh = sctp_hdr(skb);
if (sh == NULL)
break;
ad->u.net->sport = sh->source;
ad->u.net->dport = sh->dest;
break;
}
default:
ret = -EINVAL;
}
return ret;
}
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
/**
* ipv6_skb_to_auditdata : fill auditdata from skb
* @skb : the skb
* @ad : the audit data to fill
* @proto : the layer 4 protocol
*
* return 0 on success
*/
int ipv6_skb_to_auditdata(struct sk_buff *skb,
struct common_audit_data *ad, u8 *proto)
{
int offset, ret = 0;
struct ipv6hdr *ip6;
u8 nexthdr;
__be16 frag_off;
ip6 = ipv6_hdr(skb);
if (ip6 == NULL)
return -EINVAL;
ad->u.net->v6info.saddr = ip6->saddr;
ad->u.net->v6info.daddr = ip6->daddr;
ret = 0;
/* IPv6 can have several extension header before the Transport header
* skip them */
offset = skb_network_offset(skb);
offset += sizeof(*ip6);
nexthdr = ip6->nexthdr;
offset = ipv6_skip_exthdr(skb, offset, &nexthdr, &frag_off);
if (offset < 0)
return 0;
if (proto)
*proto = nexthdr;
switch (nexthdr) {
case IPPROTO_TCP: {
struct tcphdr _tcph, *th;
th = skb_header_pointer(skb, offset, sizeof(_tcph), &_tcph);
if (th == NULL)
break;
ad->u.net->sport = th->source;
ad->u.net->dport = th->dest;
break;
}
case IPPROTO_UDP: {
struct udphdr _udph, *uh;
uh = skb_header_pointer(skb, offset, sizeof(_udph), &_udph);
if (uh == NULL)
break;
ad->u.net->sport = uh->source;
ad->u.net->dport = uh->dest;
break;
}
case IPPROTO_DCCP: {
struct dccp_hdr _dccph, *dh;
dh = skb_header_pointer(skb, offset, sizeof(_dccph), &_dccph);
if (dh == NULL)
break;
ad->u.net->sport = dh->dccph_sport;
ad->u.net->dport = dh->dccph_dport;
break;
}
case IPPROTO_SCTP: {
struct sctphdr _sctph, *sh;
sh = skb_header_pointer(skb, offset, sizeof(_sctph), &_sctph);
if (sh == NULL)
break;
ad->u.net->sport = sh->source;
ad->u.net->dport = sh->dest;
break;
}
default:
ret = -EINVAL;
}
return ret;
}
#endif
static inline void print_ipv6_addr(struct audit_buffer *ab,
struct in6_addr *addr, __be16 port,
char *name1, char *name2)
{
if (!ipv6_addr_any(addr))
audit_log_format(ab, " %s=%pI6c", name1, addr);
if (port)
audit_log_format(ab, " %s=%d", name2, ntohs(port));
}
static inline void print_ipv4_addr(struct audit_buffer *ab, __be32 addr,
__be16 port, char *name1, char *name2)
{
if (addr)
audit_log_format(ab, " %s=%pI4", name1, &addr);
if (port)
audit_log_format(ab, " %s=%d", name2, ntohs(port));
}
/**
* dump_common_audit_data - helper to dump common audit data
* @a : common audit data
*
*/
static void dump_common_audit_data(struct audit_buffer *ab,
struct common_audit_data *a)
{
char comm[sizeof(current->comm)];
/*
* To keep stack sizes in check force programers to notice if they
* start making this union too large! See struct lsm_network_audit
* as an example of how to deal with large data.
*/
BUILD_BUG_ON(sizeof(a->u) > sizeof(void *)*2);
audit_log_format(ab, " pid=%d comm=", task_pid_nr(current));
audit_log_untrustedstring(ab, memcpy(comm, current->comm, sizeof(comm)));
switch (a->type) {
case LSM_AUDIT_DATA_NONE:
return;
case LSM_AUDIT_DATA_IPC:
audit_log_format(ab, " key=%d ", a->u.ipc_id);
break;
case LSM_AUDIT_DATA_CAP:
audit_log_format(ab, " capability=%d ", a->u.cap);
break;
case LSM_AUDIT_DATA_PATH: {
struct inode *inode;
audit_log_d_path(ab, " path=", &a->u.path);
inode = a->u.path.dentry->d_inode;
if (inode) {
audit_log_format(ab, " dev=");
audit_log_untrustedstring(ab, inode->i_sb->s_id);
audit_log_format(ab, " ino=%lu", inode->i_ino);
}
break;
}
case LSM_AUDIT_DATA_DENTRY: {
struct inode *inode;
audit_log_format(ab, " name=");
audit_log_untrustedstring(ab, a->u.dentry->d_name.name);
inode = a->u.dentry->d_inode;
if (inode) {
audit_log_format(ab, " dev=");
audit_log_untrustedstring(ab, inode->i_sb->s_id);
audit_log_format(ab, " ino=%lu", inode->i_ino);
}
break;
}
case LSM_AUDIT_DATA_INODE: {
struct dentry *dentry;
struct inode *inode;
inode = a->u.inode;
dentry = d_find_alias(inode);
if (dentry) {
audit_log_format(ab, " name=");
audit_log_untrustedstring(ab,
dentry->d_name.name);
dput(dentry);
}
audit_log_format(ab, " dev=");
audit_log_untrustedstring(ab, inode->i_sb->s_id);
audit_log_format(ab, " ino=%lu", inode->i_ino);
break;
}
case LSM_AUDIT_DATA_TASK: {
struct task_struct *tsk = a->u.tsk;
if (tsk) {
pid_t pid = task_pid_nr(tsk);
if (pid) {
char comm[sizeof(tsk->comm)];
audit_log_format(ab, " pid=%d comm=", pid);
audit_log_untrustedstring(ab,
memcpy(comm, tsk->comm, sizeof(comm)));
}
}
break;
}
case LSM_AUDIT_DATA_NET:
if (a->u.net->sk) {
struct sock *sk = a->u.net->sk;
struct unix_sock *u;
int len = 0;
char *p = NULL;
switch (sk->sk_family) {
case AF_INET: {
struct inet_sock *inet = inet_sk(sk);
print_ipv4_addr(ab, inet->inet_rcv_saddr,
inet->inet_sport,
"laddr", "lport");
print_ipv4_addr(ab, inet->inet_daddr,
inet->inet_dport,
"faddr", "fport");
break;
}
#if IS_ENABLED(CONFIG_IPV6)
case AF_INET6: {
struct inet_sock *inet = inet_sk(sk);
print_ipv6_addr(ab, &sk->sk_v6_rcv_saddr,
inet->inet_sport,
"laddr", "lport");
print_ipv6_addr(ab, &sk->sk_v6_daddr,
inet->inet_dport,
"faddr", "fport");
break;
}
#endif
case AF_UNIX:
u = unix_sk(sk);
if (u->path.dentry) {
audit_log_d_path(ab, " path=", &u->path);
break;
}
if (!u->addr)
break;
len = u->addr->len-sizeof(short);
p = &u->addr->name->sun_path[0];
audit_log_format(ab, " path=");
if (*p)
audit_log_untrustedstring(ab, p);
else
audit_log_n_hex(ab, p, len);
break;
}
}
switch (a->u.net->family) {
case AF_INET:
print_ipv4_addr(ab, a->u.net->v4info.saddr,
a->u.net->sport,
"saddr", "src");
print_ipv4_addr(ab, a->u.net->v4info.daddr,
a->u.net->dport,
"daddr", "dest");
break;
case AF_INET6:
print_ipv6_addr(ab, &a->u.net->v6info.saddr,
a->u.net->sport,
"saddr", "src");
print_ipv6_addr(ab, &a->u.net->v6info.daddr,
a->u.net->dport,
"daddr", "dest");
break;
}
if (a->u.net->netif > 0) {
struct net_device *dev;
/* NOTE: we always use init's namespace */
dev = dev_get_by_index(&init_net, a->u.net->netif);
if (dev) {
audit_log_format(ab, " netif=%s", dev->name);
dev_put(dev);
}
}
break;
#ifdef CONFIG_KEYS
case LSM_AUDIT_DATA_KEY:
audit_log_format(ab, " key_serial=%u", a->u.key_struct.key);
if (a->u.key_struct.key_desc) {
audit_log_format(ab, " key_desc=");
audit_log_untrustedstring(ab, a->u.key_struct.key_desc);
}
break;
#endif
case LSM_AUDIT_DATA_KMOD:
audit_log_format(ab, " kmod=");
audit_log_untrustedstring(ab, a->u.kmod_name);
break;
} /* switch (a->type) */
}
/**
* common_lsm_audit - generic LSM auditing function
* @a: auxiliary audit data
* @pre_audit: lsm-specific pre-audit callback
* @post_audit: lsm-specific post-audit callback
*
* setup the audit buffer for common security information
* uses callback to print LSM specific information
*/
void common_lsm_audit(struct common_audit_data *a,
void (*pre_audit)(struct audit_buffer *, void *),
void (*post_audit)(struct audit_buffer *, void *))
{
struct audit_buffer *ab;
if (a == NULL)
return;
/* we use GFP_ATOMIC so we won't sleep */
ab = audit_log_start(current->audit_context, GFP_ATOMIC | __GFP_NOWARN,
AUDIT_AVC);
if (ab == NULL)
return;
if (pre_audit)
pre_audit(ab, a);
dump_common_audit_data(ab, a);
if (post_audit)
post_audit(ab, a);
audit_log_end(ab);
}
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