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AUDIT: buffer audit msgs directly to skb
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Drop the use of a tmp buffer in the audit_buffer, and just buffer
directly to the skb.  All header data that was temporarily stored in
the audit_buffer can now be stored directly in the netlink header in
the skb.  Resize skb as needed.  This eliminates the extra copy (and
the audit_log_move function which was responsible for copying).

Signed-off-by: Chris Wright <chrisw@osdl.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
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Chris Wright authored and David Woodhouse committed May 6, 2005
1 parent 8fc6115 commit 5ac52f3
Showing 1 changed file with 46 additions and 76 deletions.
122 changes: 46 additions & 76 deletions kernel/audit.c
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Original file line number Diff line number Diff line change
Expand Up @@ -138,16 +138,18 @@ struct audit_buffer {
struct list_head list;
struct sk_buff *skb; /* formatted skb ready to send */
struct audit_context *ctx; /* NULL or associated context */
int len; /* used area of tmp */
int size; /* size of tmp */
char *tmp;
int type;
int pid;
};

void audit_set_type(struct audit_buffer *ab, int type)
{
ab->type = type;
struct nlmsghdr *nlh = (struct nlmsghdr *)ab->skb->data;
nlh->nlmsg_type = type;
}

static void audit_set_pid(struct audit_buffer *ab, pid_t pid)
{
struct nlmsghdr *nlh = (struct nlmsghdr *)ab->skb->data;
nlh->nlmsg_pid = pid;
}

struct audit_entry {
Expand Down Expand Up @@ -405,8 +407,8 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
(int)(nlh->nlmsg_len
- ((char *)data - (char *)nlh)),
loginuid, (char *)data);
ab->type = AUDIT_USER;
ab->pid = pid;
audit_set_type(ab, AUDIT_USER);
audit_set_pid(ab, pid);
audit_log_end(ab);
break;
case AUDIT_ADD:
Expand Down Expand Up @@ -476,42 +478,7 @@ static void audit_receive(struct sock *sk, int length)
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;
struct nlmsghdr *nlh;
char *start;
int len = NLMSG_SPACE(0) + ab->len + 1;

/* possible resubmission */
if (ab->skb)
return;

skb = alloc_skb(len, GFP_ATOMIC);
if (!skb) {
/* Lose information in ab->tmp */
audit_log_lost("out of memory in audit_log_move");
return;
}
ab->skb = skb;
nlh = (struct nlmsghdr *)skb_put(skb, NLMSG_SPACE(0));
nlh->nlmsg_type = ab->type;
nlh->nlmsg_len = ab->len;
nlh->nlmsg_flags = 0;
nlh->nlmsg_pid = ab->pid;
nlh->nlmsg_seq = 0;
start = skb_put(skb, ab->len);
memcpy(start, ab->tmp, ab->len);
}

/* Iterate over the skbuff in the audit_buffer, sending their contents
* to user space. */
/* Grab skbuff from the audit_buffer and send to user space. */
static inline int audit_log_drain(struct audit_buffer *ab)
{
struct sk_buff *skb = ab->skb;
Expand All @@ -520,6 +487,8 @@ static inline int audit_log_drain(struct audit_buffer *ab)
int retval = 0;

if (audit_pid) {
struct nlmsghdr *nlh = (struct nlmsghdr *)skb->data;
nlh->nlmsg_len = skb->len;
skb_get(skb); /* because netlink_* frees */
retval = netlink_unicast(audit_sock, skb, audit_pid,
MSG_DONTWAIT);
Expand All @@ -544,7 +513,6 @@ static inline int audit_log_drain(struct audit_buffer *ab)
skb->data[offset + len] = '\0';
printk(KERN_ERR "%s\n", skb->data + offset);
}
kfree_skb(skb);
}
return 0;
}
Expand Down Expand Up @@ -615,7 +583,8 @@ static void audit_buffer_free(struct audit_buffer *ab)
if (!ab)
return;

kfree(ab->tmp);
if (ab->skb)
kfree_skb(ab->skb);
atomic_dec(&audit_backlog);
spin_lock_irqsave(&audit_freelist_lock, flags);
if (++audit_freelist_count > AUDIT_MAXFREE)
Expand All @@ -630,6 +599,7 @@ static struct audit_buffer * audit_buffer_alloc(struct audit_context *ctx,
{
unsigned long flags;
struct audit_buffer *ab = NULL;
struct nlmsghdr *nlh;

spin_lock_irqsave(&audit_freelist_lock, flags);
if (!list_empty(&audit_freelist)) {
Expand All @@ -647,16 +617,16 @@ static struct audit_buffer * audit_buffer_alloc(struct audit_context *ctx,
}
atomic_inc(&audit_backlog);

ab->tmp = kmalloc(AUDIT_BUFSIZ, GFP_ATOMIC);
if (!ab->tmp)
ab->skb = alloc_skb(AUDIT_BUFSIZ, GFP_ATOMIC);
if (!ab->skb)
goto err;

ab->skb = NULL;
ab->ctx = ctx;
ab->len = 0;
ab->size = AUDIT_BUFSIZ;
ab->type = AUDIT_KERNEL;
ab->pid = 0;
nlh = (struct nlmsghdr *)skb_put(ab->skb, NLMSG_SPACE(0));
nlh->nlmsg_type = AUDIT_KERNEL;
nlh->nlmsg_flags = 0;
nlh->nlmsg_pid = 0;
nlh->nlmsg_seq = 0;
return ab;
err:
audit_buffer_free(ab);
Expand Down Expand Up @@ -711,25 +681,22 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx)
}

/**
* audit_expand - expand tmp buffer in the audit buffer
* audit_expand - expand skb in the audit buffer
* @ab: audit_buffer
*
* Returns 0 (no space) on failed expansion, or available space if
* successful.
*/
static inline int audit_expand(struct audit_buffer *ab)
{
char *tmp;
int len = ab->size + AUDIT_BUFSIZ;

tmp = kmalloc(len, GFP_ATOMIC);
if (!tmp)
struct sk_buff *skb = ab->skb;
int ret = pskb_expand_head(skb, skb_headroom(skb), AUDIT_BUFSIZ,
GFP_ATOMIC);
if (ret < 0) {
audit_log_lost("out of memory in audit_expand");
return 0;
memcpy(tmp, ab->tmp, ab->len);
kfree(ab->tmp);
ab->tmp = tmp;
ab->size = len;
return ab->size - ab->len;
}
return skb_tailroom(skb);
}

/* Format an audit message into the audit buffer. If there isn't enough
Expand All @@ -740,27 +707,30 @@ static void audit_log_vformat(struct audit_buffer *ab, const char *fmt,
va_list args)
{
int len, avail;
struct sk_buff *skb;

if (!ab)
return;

avail = ab->size - ab->len;
if (avail <= 0) {
BUG_ON(!ab->skb);
skb = ab->skb;
avail = skb_tailroom(skb);
if (avail == 0) {
avail = audit_expand(ab);
if (!avail)
goto out;
}
len = vsnprintf(ab->tmp + ab->len, avail, fmt, args);
len = vsnprintf(skb->tail, 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. */
avail = audit_expand(ab);
if (!avail)
goto out;
len = vsnprintf(ab->tmp + ab->len, avail, fmt, args);
len = vsnprintf(skb->tail, avail, fmt, args);
}
ab->len += (len < avail) ? len : avail;
skb_put(skb, (len < avail) ? len : avail);
out:
return;
}
Expand Down Expand Up @@ -808,21 +778,22 @@ void audit_log_d_path(struct audit_buffer *ab, const char *prefix,
struct dentry *dentry, struct vfsmount *vfsmnt)
{
char *p;
struct sk_buff *skb = ab->skb;
int len, avail;

if (prefix)
audit_log_format(ab, " %s", prefix);

avail = ab->size - ab->len;
p = d_path(dentry, vfsmnt, ab->tmp + ab->len, avail);
avail = skb_tailroom(skb);
p = d_path(dentry, vfsmnt, skb->tail, avail);
if (IS_ERR(p)) {
/* FIXME: can we save some information here? */
audit_log_format(ab, "<toolong>");
} else {
/* path isn't at start of buffer */
len = (ab->tmp + ab->size - 1) - p;
memmove(ab->tmp + ab->len, p, len);
ab->len += len;
/* path isn't at start of buffer */
len = ((char *)skb->tail + avail - 1) - p;
memmove(skb->tail, p, len);
skb_put(skb, len);
}
}

Expand Down Expand Up @@ -873,7 +844,6 @@ static void audit_log_end_fast(struct audit_buffer *ab)
if (!audit_rate_check()) {
audit_log_lost("rate limit exceeded");
} else {
audit_log_move(ab);
if (audit_log_drain(ab))
return;
}
Expand Down

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