[PATCH] audit: fix size of netlink messages
Nicolas Dichtel
nicolas.dichtel at 6wind.com
Fri Jun 7 16:24:02 UTC 2013
Put Thomas in CC.
Le 07/06/2013 17:43, Eric Paris a écrit :
> On Fri, 2013-06-07 at 17:25 +0200, Nicolas Dichtel wrote:
>
> NAK.
>
> I tried this once before and as I recal userspace actually expected the
> stoopidity of being unaligned and broke :-(
On which userspace tools do you think?
For example, in the libnl, the function which tries to get the next netlink
message expects this alignment:
struct nlmsghdr *nlmsg_next(struct nlmsghdr *nlh, int *remaining)
{
int totlen = NLMSG_ALIGN(nlh->nlmsg_len);
*remaining -= totlen;
return (struct nlmsghdr *) ((unsigned char *) nlh + totlen);
}
http://www.infradead.org/~tgr/libnl/doc/core.html#_message_parsing_amp_construction
>
>> Netlink messages must be aligned on NLMSG_ALIGNTO (4 bytes), thus we need to
>> update the skb length before sending it to userspace.
>>
>> This patch adds the needed padding to be compliant with this requirement.
>>
>> Signed-off-by: Nicolas Dichtel <nicolas.dichtel at 6wind.com>
>> ---
>> kernel/audit.c | 11 +++++++++++
>> 1 file changed, 11 insertions(+)
>>
>> diff --git a/kernel/audit.c b/kernel/audit.c
>> index 21c7fa6..31d213a 100644
>> --- a/kernel/audit.c
>> +++ b/kernel/audit.c
>> @@ -1669,6 +1669,17 @@ void audit_log_end(struct audit_buffer *ab)
>> struct nlmsghdr *nlh = nlmsg_hdr(ab->skb);
>> nlh->nlmsg_len = ab->skb->len - NLMSG_HDRLEN;
>>
>> + if (NLMSG_ALIGN(ab->skb->len) != ab->skb->len) {
Here, I think it's better to use nlmsg_padlen().
>> + unsigned int pad = NLMSG_ALIGN(ab->skb->len) -
>> + ab->skb->len;
>> +
>> + if (skb_tailroom(ab->skb) >= pad)
>> + skb_put(ab->skb, pad);
>> + else if (pskb_expand_head(ab->skb, 0, pad,
>> + GFP_KERNEL) < 0)
>> + audit_log_lost("out of memory in audit_log_end");
>> + }
>> +
>> if (audit_pid) {
>> skb_queue_tail(&audit_skb_queue, ab->skb);
>> wake_up_interruptible(&kauditd_wait);
>
>
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