/* audit.c -- Auditing support -*- linux-c -*- * Gateway between the kernel (e.g., selinux) and the user-space audit daemon. * System-call specific features have moved to auditsc.c * * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina. * All Rights Reserved. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * * Written by Rickard E. (Rik) Faith * * Goals: 1) Integrate fully with SELinux. * 2) Minimal run-time overhead: * a) Minimal when syscall auditing is disabled (audit_enable=0). * b) Small when syscall auditing is enabled and no audit record * is generated (defer as much work as possible to record * generation time): * i) context is allocated, * ii) names from getname are stored without a copy, and * iii) inode information stored from path_lookup. * 3) Ability to disable syscall auditing at boot time (audit=0). * 4) Usable by other parts of the kernel (if audit_log* is called, * then a syscall record will be generated automatically for the * current syscall). * 5) Netlink interface to user-space. * 6) Support low-overhead kernel-based filtering to minimize the * information that must be passed to user-space. * * Example user-space utilities: http://people.redhat.com/faith/audit/ */ #include #include #include #include #include #include #include #include #include /* No auditing will take place until audit_initialized != 0. * (Initialization happens after skb_init is called.) */ static int audit_initialized; /* No syscall auditing will take place unless audit_enabled != 0. */ int audit_enabled; /* Default state when kernel boots without any parameters. */ static int audit_default; /* If auditing cannot proceed, audit_failure selects what happens. */ static int audit_failure = AUDIT_FAIL_PRINTK; /* If audit records are to be written to the netlink socket, audit_pid * contains the (non-zero) pid. */ static int audit_pid; /* If audit_limit is non-zero, limit the rate of sending audit records * to that number per second. This prevents DoS attacks, but results in * audit records being dropped. */ static int audit_rate_limit; /* Number of outstanding audit_buffers allowed. */ static int audit_backlog_limit = 64; static atomic_t audit_backlog = ATOMIC_INIT(0); /* Records can be lost in several ways: 0) [suppressed in audit_alloc] 1) out of memory in audit_log_start [kmalloc of struct audit_buffer] 2) out of memory in audit_log_move [alloc_skb] 3) suppressed due to audit_rate_limit 4) suppressed due to audit_backlog_limit */ static atomic_t audit_lost = ATOMIC_INIT(0); /* The netlink socket. */ static struct sock *audit_sock; /* There are two lists of audit buffers. The txlist contains audit * buffers that cannot be sent immediately to the netlink device because * we are in an irq context (these are sent later in a tasklet). * * The second list is a list of pre-allocated audit buffers (if more * than AUDIT_MAXFREE are in use, the audit buffer is freed instead of * being placed on the freelist). */ static DEFINE_SPINLOCK(audit_txlist_lock); static DEFINE_SPINLOCK(audit_freelist_lock); static int audit_freelist_count = 0; static LIST_HEAD(audit_txlist); static LIST_HEAD(audit_freelist); /* There are three lists of rules -- one to search at task creation * time, one to search at syscall entry time, and another to search at * syscall exit time. */ static LIST_HEAD(audit_tsklist); static LIST_HEAD(audit_entlist); static LIST_HEAD(audit_extlist); /* The netlink socket is only to be read by 1 CPU, which lets us assume * that list additions and deletions never happen simultaneiously in * auditsc.c */ static DECLARE_MUTEX(audit_netlink_sem); /* AUDIT_BUFSIZ is the size of the temporary buffer used for formatting * audit records. Since printk uses a 1024 byte buffer, this buffer * should be at least that large. */ #define AUDIT_BUFSIZ 1024 /* AUDIT_MAXFREE is the number of empty audit_buffers we keep on the * audit_freelist. Doing so eliminates many kmalloc/kfree calls. */ #define AUDIT_MAXFREE (2*NR_CPUS) /* The audit_buffer is used when formatting an audit record. The caller * locks briefly to get the record off the freelist or to allocate the * buffer, and locks briefly to send the buffer to the netlink layer or * to place it on a transmit queue. Multiple audit_buffers can be in * use simultaneously. */ struct audit_buffer { struct list_head list; struct sk_buff_head sklist; /* formatted skbs ready to send */ struct audit_context *ctx; /* NULL or associated context */ int len; /* used area of tmp */ char tmp[AUDIT_BUFSIZ]; /* Pointer to header and contents */ struct nlmsghdr *nlh; int total; int type; int pid; int count; /* Times requeued */ }; void audit_set_type(struct audit_buffer *ab, int type) { ab->type = type; } struct audit_entry { struct list_head list; struct audit_rule rule; }; static void audit_log_end_irq(struct audit_buffer *ab); static void audit_log_end_fast(struct audit_buffer *ab); static void audit_panic(const char *message) { switch (audit_failure) { case AUDIT_FAIL_SILENT: break; case AUDIT_FAIL_PRINTK: printk(KERN_ERR "audit: %s\n", message); break; case AUDIT_FAIL_PANIC: panic("audit: %s\n", message); break; } } static inline int audit_rate_check(void) { static unsigned long last_check = 0; static int messages = 0; static DEFINE_SPINLOCK(lock); unsigned long flags; unsigned long now; unsigned long elapsed; int retval = 0; if (!audit_rate_limit) return 1; spin_lock_irqsave(&lock, flags); if (++messages < audit_rate_limit) { retval = 1; } else { now = jiffies; elapsed = now - last_check; if (elapsed > HZ) { last_check = now; messages = 0; retval = 1; } } spin_unlock_irqrestore(&lock, flags); return retval; } /* Emit at least 1 message per second, even if audit_rate_check is * throttling. */ void audit_log_lost(const char *message) { static unsigned long last_msg = 0; static DEFINE_SPINLOCK(lock); unsigned long flags; unsigned long now; int print; atomic_inc(&audit_lost); print = (audit_failure == AUDIT_FAIL_PANIC || !audit_rate_limit); if (!print) { spin_lock_irqsave(&lock, flags); now = jiffies; if (now - last_msg > HZ) { print = 1; last_msg = now; } spin_unlock_irqrestore(&lock, flags); } if (print) { printk(KERN_WARNING "audit: audit_lost=%d audit_backlog=%d" " audit_rate_limit=%d audit_backlog_limit=%d\n", atomic_read(&audit_lost), atomic_read(&audit_backlog), audit_rate_limit, audit_backlog_limit); audit_panic(message); } } static int audit_set_rate_limit(int limit) { int old = audit_rate_limit; audit_rate_limit = limit; audit_log(current->audit_context, "audit_rate_limit=%d old=%d", audit_rate_limit, old); return old; } static int audit_set_backlog_limit(int limit) { int old = audit_backlog_limit; audit_backlog_limit = limit; audit_log(current->audit_context, "audit_backlog_limit=%d old=%d", audit_backlog_limit, old); return old; } static int audit_set_enabled(int state) { int old = audit_enabled; if (state != 0 && state != 1) return -EINVAL; audit_enabled = state; audit_log(current->audit_context, "audit_enabled=%d old=%d", audit_enabled, old); return old; } static int audit_set_failure(int state) { int old = audit_failure; if (state != AUDIT_FAIL_SILENT && state != AUDIT_FAIL_PRINTK && state != AUDIT_FAIL_PANIC) return -EINVAL; audit_failure = state; audit_log(current->audit_context, "audit_failure=%d old=%d", audit_failure, old); return old; } #ifdef CONFIG_NET void audit_send_reply(int pid, int seq, int type, int done, int multi, void *payload, int size) { struct sk_buff *skb; struct nlmsghdr *nlh; int len = NLMSG_SPACE(size); void *data; int flags = multi ? NLM_F_MULTI : 0; int t = done ? NLMSG_DONE : type; skb = alloc_skb(len, GFP_KERNEL); if (!skb) goto nlmsg_failure; nlh = NLMSG_PUT(skb, pid, seq, t, len - sizeof(*nlh)); nlh->nlmsg_flags = flags; data = NLMSG_DATA(nlh); memcpy(data, payload, size); netlink_unicast(audit_sock, skb, pid, MSG_DONTWAIT); return; nlmsg_failure: /* Used by NLMSG_PUT */ if (skb) kfree_skb(skb); } /* * Check for appropriate CAP_AUDIT_ capabilities on incoming audit * control messages. */ static int audit_netlink_ok(kernel_cap_t eff_cap, u16 msg_type) { int err = 0; switch (msg_type) { case AUDIT_GET: case AUDIT_LIST: case AUDIT_SET: case AUDIT_ADD: case AUDIT_DEL: if (!cap_raised(eff_cap, CAP_AUDIT_CONTROL)) err = -EPERM; break; case AUDIT_USER: if (!cap_raised(eff_cap, CAP_AUDIT_WRITE)) err = -EPERM; break; default: /* bad msg */ err = -EINVAL; } return err; } static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh) { u32 uid, pid, seq; void *data; struct audit_status *status_get, status_set; int err; struct audit_buffer *ab; u16 msg_type = nlh->nlmsg_type; err = audit_netlink_ok(NETLINK_CB(skb).eff_cap, msg_type); if (err) return err; pid = NETLINK_CREDS(skb)->pid; uid = NETLINK_CREDS(skb)->uid; seq = nlh->nlmsg_seq; data = NLMSG_DATA(nlh); switch (msg_type) { case AUDIT_GET: status_set.enabled = audit_enabled; status_set.failure = audit_failure; status_set.pid = audit_pid; status_set.rate_limit = audit_rate_limit; status_set.backlog_limit = audit_backlog_limit; status_set.lost = atomic_read(&audit_lost); status_set.backlog = atomic_read(&audit_backlog); audit_send_reply(NETLINK_CB(skb).pid, seq, AUDIT_GET, 0, 0, &status_set, sizeof(status_set)); break; case AUDIT_SET: if (nlh->nlmsg_len < sizeof(struct audit_status)) return -EINVAL; status_get = (struct audit_status *)data; if (status_get->mask & AUDIT_STATUS_ENABLED) { err = audit_set_enabled(status_get->enabled); if (err < 0) return err; } if (status_get->mask & AUDIT_STATUS_FAILURE) { err = audit_set_failure(status_get->failure); if (err < 0) return err; } if (status_get->mask & AUDIT_STATUS_PID) { int old = audit_pid; audit_pid = status_get->pid; audit_log(current->audit_context, "audit_pid=%d old=%d", audit_pid, old); } if (status_get->mask & AUDIT_STATUS_RATE_LIMIT) audit_set_rate_limit(status_get->rate_limit); if (status_get->mask & AUDIT_STATUS_BACKLOG_LIMIT) audit_set_backlog_limit(status_get->backlog_limit); break; case AUDIT_USER: ab = audit_log_start(NULL); if (!ab) break; /* audit_panic has been called */ audit_log_format(ab, "user pid=%d uid=%d length=%d msg='%.1024s'", pid, uid, (int)(nlh->nlmsg_len - ((char *)data - (char *)nlh)), (char *)data); ab->type = AUDIT_USER; ab->pid = pid; audit_log_end(ab); break; case AUDIT_ADD: case AUDIT_DEL: if (nlh->nlmsg_len < sizeof(struct audit_rule)) return -EINVAL; /* fallthrough */ case AUDIT_LIST: #ifdef CONFIG_AUDITSYSCALL err = audit_receive_filter(nlh->nlmsg_type, NETLINK_CB(skb).pid, uid, seq, data); #else err = -EOPNOTSUPP; #endif break; default: err = -EINVAL; break; } return err < 0 ? err : 0; } /* Get message from skb (based on rtnetlink_rcv_skb). Each message is * processed by audit_receive_msg. Malformed skbs with wrong length are * discarded silently. */ static int audit_receive_skb(struct sk_buff *skb) { int err; struct nlmsghdr *nlh; u32 rlen; while (skb->len >= NLMSG_SPACE(0)) { nlh = (struct nlmsghdr *)skb->data; if (nlh->nlmsg_len < sizeof(*nlh) || skb->len < nlh->nlmsg_len) return 0; rlen = NLMSG_ALIGN(nlh->nlmsg_len); if (rlen > skb->len) rlen = skb->len; if ((err = audit_receive_msg(skb, nlh))) { netlink_ack(skb, nlh, err); } else if (nlh->nlmsg_flags & NLM_F_ACK) netlink_ack(skb, nlh, 0); skb_pull(skb, rlen); } return 0; } /* Receive messages from netlink socket. */ static void audit_receive(struct sock *sk, int length) { struct sk_buff *skb; if (down_trylock(&audit_netlink_sem)) return; /* FIXME: this must not cause starvation */ while ((skb = skb_dequeue(&sk->sk_receive_queue))) { if (audit_receive_skb(skb) && skb->len) skb_queue_head(&sk->sk_receive_queue, skb); else kfree_skb(skb); } up(&audit_netlink_sem); } /* Move data from tmp buffer into an skb. This is an extra copy, and * that is unfortunate. However, the copy will only occur when a record * is being written to user space, which is already a high-overhead * operation. (Elimination of the copy is possible, for example, by * writing directly into a pre-allocated skb, at the cost of wasting * memory. */ static void audit_log_move(struct audit_buffer *ab) { struct sk_buff *skb; char *start; int extra = ab->nlh ? 0 : NLMSG_SPACE(0); /* possible resubmission */ if (ab->len == 0) return; skb = skb_peek(&ab->sklist); if (!skb || skb_tailroom(skb) <= ab->len + extra) { skb = alloc_skb(2 * ab->len + extra, GFP_ATOMIC); if (!skb) { ab->len = 0; /* Lose information in ab->tmp */ audit_log_lost("out of memory in audit_log_move"); return; } __skb_queue_tail(&ab->sklist, skb); if (!ab->nlh) ab->nlh = (struct nlmsghdr *)skb_put(skb, NLMSG_SPACE(0)); } start = skb_put(skb, ab->len); memcpy(start, ab->tmp, ab->len); ab->len = 0; } /* Iterate over the skbuff in the audit_buffer, sending their contents * to user space. */ static inline int audit_log_drain(struct audit_buffer *ab) { struct sk_buff *skb; while ((skb = skb_dequeue(&ab->sklist))) { int retval = 0; if (audit_pid) { if (ab->nlh) { ab->nlh->nlmsg_len = ab->total; ab->nlh->nlmsg_type = ab->type; ab->nlh->nlmsg_flags = 0; ab->nlh->nlmsg_seq = 0; ab->nlh->nlmsg_pid = ab->pid; } skb_get(skb); /* because netlink_* frees */ retval = netlink_unicast(audit_sock, skb, audit_pid, MSG_DONTWAIT); } if (retval == -EAGAIN && ab->count < 5) { ++ab->count; skb_queue_tail(&ab->sklist, skb); audit_log_end_irq(ab); return 1; } if (retval < 0) { if (retval == -ECONNREFUSED) { printk(KERN_ERR "audit: *NO* daemon at audit_pid=%d\n", audit_pid); audit_pid = 0; } else audit_log_lost("netlink socket too busy"); } if (!audit_pid) { /* No daemon */ int offset = ab->nlh ? NLMSG_SPACE(0) : 0; int len = skb->len - offset; printk(KERN_ERR "%*.*s\n", len, len, skb->data + offset); } kfree_skb(skb); ab->nlh = NULL; } return 0; } /* Initialize audit support at boot time. */ static int __init audit_init(void) { printk(KERN_INFO "audit: initializing netlink socket (%s)\n", audit_default ? "enabled" : "disabled"); audit_sock = netlink_kernel_create(NETLINK_AUDIT, audit_receive); if (!audit_sock) audit_panic("cannot initialize netlink socket"); audit_initialized = 1; audit_enabled = audit_default; audit_log(NULL, "initialized"); return 0; } #else /* Without CONFIG_NET, we have no skbuffs. For now, print what we have * in the buffer. */ static void audit_log_move(struct audit_buffer *ab) { printk(KERN_ERR "%*.*s\n", ab->len, ab->len, ab->tmp); ab->len = 0; } static inline int audit_log_drain(struct audit_buffer *ab) { return 0; } /* Initialize audit support at boot time. */ int __init audit_init(void) { printk(KERN_INFO "audit: initializing WITHOUT netlink support\n"); audit_sock = NULL; audit_pid = 0; audit_initialized = 1; audit_enabled = audit_default; audit_log(NULL, "initialized"); return 0; } #endif __initcall(audit_init); /* Process kernel command-line parameter at boot time. audit=0 or audit=1. */ static int __init audit_enable(char *str) { audit_default = !!simple_strtol(str, NULL, 0); printk(KERN_INFO "audit: %s%s\n", audit_default ? "enabled" : "disabled", audit_initialized ? "" : " (after initialization)"); if (audit_initialized) audit_enabled = audit_default; return 0; } __setup("audit=", audit_enable); /* Obtain an audit buffer. This routine does locking to obtain the * audit buffer, but then no locking is required for calls to * audit_log_*format. If the tsk is a task that is currently in a * syscall, then the syscall is marked as auditable and an audit record * will be written at syscall exit. If there is no associated task, tsk * should be NULL. */ struct audit_buffer *audit_log_start(struct audit_context *ctx) { struct audit_buffer *ab = NULL; unsigned long flags; struct timespec t; unsigned int serial; if (!audit_initialized) return NULL; if (audit_backlog_limit && atomic_read(&audit_backlog) > audit_backlog_limit) { if (audit_rate_check()) printk(KERN_WARNING "audit: audit_backlog=%d > " "audit_backlog_limit=%d\n", atomic_read(&audit_backlog), audit_backlog_limit); audit_log_lost("backlog limit exceeded"); return NULL; } spin_lock_irqsave(&audit_freelist_lock, flags); if (!list_empty(&audit_freelist)) { ab = list_entry(audit_freelist.next, struct audit_buffer, list); list_del(&ab->list); --audit_freelist_count; } spin_unlock_irqrestore(&audit_freelist_lock, flags); if (!ab) ab = kmalloc(sizeof(*ab), GFP_ATOMIC); if (!ab) { audit_log_lost("out of memory in audit_log_start"); return NULL; } atomic_inc(&audit_backlog); skb_queue_head_init(&ab->sklist); ab->ctx = ctx; ab->len = 0; ab->nlh = NULL; ab->total = 0; ab->type = AUDIT_KERNEL; ab->pid = 0; ab->count = 0; #ifdef CONFIG_AUDITSYSCALL if (ab->ctx) audit_get_stamp(ab->ctx, &t, &serial); else #endif { t = CURRENT_TIME; serial = 0; } audit_log_format(ab, "audit(%lu.%03lu:%u): ", t.tv_sec, t.tv_nsec/1000000, serial); return ab; } /* Format an audit message into the audit buffer. If there isn't enough * room in the audit buffer, more room will be allocated and vsnprint * will be called a second time. Currently, we assume that a printk * can't format message larger than 1024 bytes, so we don't either. */ static void audit_log_vformat(struct audit_buffer *ab, const char *fmt, va_list args) { int len, avail; if (!ab) return; avail = sizeof(ab->tmp) - ab->len; if (avail <= 0) { audit_log_move(ab); avail = sizeof(ab->tmp) - ab->len; } len = vsnprintf(ab->tmp + ab->len, avail, fmt, args); if (len >= avail) { /* The printk buffer is 1024 bytes long, so if we get * here and AUDIT_BUFSIZ is at least 1024, then we can * log everything that printk could have logged. */ audit_log_move(ab); avail = sizeof(ab->tmp) - ab->len; len = vsnprintf(ab->tmp + ab->len, avail, fmt, args); } ab->len += (len < avail) ? len : avail; ab->total += (len < avail) ? len : avail; } /* Format a message into the audit buffer. All the work is done in * audit_log_vformat. */ void audit_log_format(struct audit_buffer *ab, const char *fmt, ...) { va_list args; if (!ab) return; va_start(args, fmt); audit_log_vformat(ab, fmt, args); va_end(args); } void audit_log_hex(struct audit_buffer *ab, const unsigned char *buf, size_t len) { int i; for (i=0; i 0x7f) { audit_log_hex(ab, string, strlen(string)); return; } p++; } audit_log_format(ab, "\"%s\"", string); } /* This is a helper-function to print the d_path without using a static * buffer or allocating another buffer in addition to the one in * audit_buffer. */ void audit_log_d_path(struct audit_buffer *ab, const char *prefix, struct dentry *dentry, struct vfsmount *vfsmnt) { char *p; int len, avail; if (prefix) audit_log_format(ab, " %s", prefix); if (ab->len > 128) audit_log_move(ab); avail = sizeof(ab->tmp) - ab->len; p = d_path(dentry, vfsmnt, ab->tmp + ab->len, avail); if (IS_ERR(p)) { /* FIXME: can we save some information here? */ audit_log_format(ab, ""); } else { /* path isn't at start of buffer */ len = (ab->tmp + sizeof(ab->tmp) - 1) - p; memmove(ab->tmp + ab->len, p, len); ab->len += len; ab->total += len; } } /* Remove queued messages from the audit_txlist and send them to userspace. */ static void audit_tasklet_handler(unsigned long arg) { LIST_HEAD(list); struct audit_buffer *ab; unsigned long flags; spin_lock_irqsave(&audit_txlist_lock, flags); list_splice_init(&audit_txlist, &list); spin_unlock_irqrestore(&audit_txlist_lock, flags); while (!list_empty(&list)) { ab = list_entry(list.next, struct audit_buffer, list); list_del(&ab->list); audit_log_end_fast(ab); } } static DECLARE_TASKLET(audit_tasklet, audit_tasklet_handler, 0); /* The netlink_* functions cannot be called inside an irq context, so * the audit buffer is places on a queue and a tasklet is scheduled to * remove them from the queue outside the irq context. May be called in * any context. */ static void audit_log_end_irq(struct audit_buffer *ab) { unsigned long flags; if (!ab) return; spin_lock_irqsave(&audit_txlist_lock, flags); list_add_tail(&ab->list, &audit_txlist); spin_unlock_irqrestore(&audit_txlist_lock, flags); tasklet_schedule(&audit_tasklet); } /* Send the message in the audit buffer directly to user space. May not * be called in an irq context. */ static void audit_log_end_fast(struct audit_buffer *ab) { unsigned long flags; BUG_ON(in_irq()); if (!ab) return; if (!audit_rate_check()) { audit_log_lost("rate limit exceeded"); } else { audit_log_move(ab); if (audit_log_drain(ab)) return; } atomic_dec(&audit_backlog); spin_lock_irqsave(&audit_freelist_lock, flags); if (++audit_freelist_count > AUDIT_MAXFREE) kfree(ab); else list_add(&ab->list, &audit_freelist); spin_unlock_irqrestore(&audit_freelist_lock, flags); } /* Send or queue the message in the audit buffer, depending on the * current context. (A convenience function that may be called in any * context.) */ void audit_log_end(struct audit_buffer *ab) { if (in_irq()) audit_log_end_irq(ab); else audit_log_end_fast(ab); } /* Log an audit record. This is a convenience function that calls * audit_log_start, audit_log_vformat, and audit_log_end. It may be * called in any context. */ void audit_log(struct audit_context *ctx, const char *fmt, ...) { struct audit_buffer *ab; va_list args; ab = audit_log_start(ctx); if (ab) { va_start(args, fmt); audit_log_vformat(ab, fmt, args); va_end(args); audit_log_end(ab); } }