[PATCH 3/3] buffer audit msgs directly to skb

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(a)osdl.org&gt; --- kernel/audit.c | 122 +++++++++++++++++++++------------------------------------ 1 files changed, 46 insertions(+), 76 deletions(-) kernel/audit.c: 24dbd7ce6967f002e15e8dd6d0b557563067a209 --- k/kernel/audit.c +++ l/kernel/audit.c @@ -134,16 +134,18 @@ 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 { @@ -399,8 +401,8 @@ static int audit_receive_msg(struct sk_b (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: @@ -464,42 +466,7 @@ static void audit_receive(struct sock *s 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; @@ -508,6 +475,8 @@ static inline int audit_log_drain(struct 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); @@ -532,7 +501,6 @@ static inline int audit_log_drain(struct skb->data[offset + len] = '\0'; printk(KERN_ERR "%s\n", skb->data + offset); } - kfree_skb(skb); } return 0; } @@ -603,7 +571,8 @@ static void audit_buffer_free(struct aud 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) @@ -618,6 +587,7 @@ static struct audit_buffer * audit_buffe { unsigned long flags; struct audit_buffer *ab = NULL; + struct nlmsghdr *nlh; spin_lock_irqsave(&audit_freelist_lock, flags); if (!list_empty(&audit_freelist)) { @@ -635,16 +605,16 @@ static struct audit_buffer * audit_buffe } 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); @@ -699,7 +669,7 @@ struct audit_buffer *audit_log_start(str } /** - * 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 @@ -707,17 +677,14 @@ struct audit_buffer *audit_log_start(str */ 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 @@ -728,17 +695,20 @@ static void audit_log_vformat(struct aud 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 @@ -746,9 +716,9 @@ static void audit_log_vformat(struct aud 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; } @@ -796,21 +766,22 @@ void audit_log_d_path(struct audit_buffe 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); } } @@ -861,7 +832,6 @@ static void audit_log_end_fast(struct au if (!audit_rate_check()) { audit_log_lost("rate limit exceeded"); } else { - audit_log_move(ab); if (audit_log_drain(ab)) return; }