Re: [PATCH V3] audit: normalize NETFILTER_PKT

On Wed, Mar 1, 2017 at 5:34 PM, Richard Guy Briggs <rgb(a)redhat.com&gt; wrote: > On 2017-03-01 17:19, Paul Moore wrote: >> On Wed, Mar 1, 2017 at 11:28 AM, Richard Guy Briggs <rgb(a)redhat.com&gt; wrote: >> > On 2017-02-28 17:22, Paul Moore wrote: >> >> On Sun, Feb 26, 2017 at 3:49 PM, Richard Guy Briggs <rgb(a)redhat.com&gt; wrote: >> >> > Eliminate flipping in and out of message fields, dropping fields in the process. >> >> > >> >> > Sample raw message format IPv4 UDP: >> >> > type=NETFILTER_PKT msg=audit(1487874761.386:228): mark=0xae8a2732 saddr=127.0.0.1 daddr=127.0.0.1 proto=17^] >> >> > Sample raw message format IPv6 ICMP6: >> >> > type=NETFILTER_PKT msg=audit(1487874761.381:227): mark=0x223894b7 saddr=::1 daddr=::1 proto=58^] >> >> > >> >> > Issue: https://github.com/linux-audit/audit-kernel/issues/11 >> >> > Test case: https://github.com/linux-audit/audit-testsuite/issues/43 >> >> > >> >> > Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com&gt; >> >> > --- >> >> > net/netfilter/xt_AUDIT.c | 122 ++++++++++----------------------------------- >> >> > 1 files changed, 27 insertions(+), 95 deletions(-) >> >> > >> >> > diff --git a/net/netfilter/xt_AUDIT.c b/net/netfilter/xt_AUDIT.c >> >> > index 4973cbd..945fa29 100644 >> >> > --- a/net/netfilter/xt_AUDIT.c >> >> > +++ b/net/netfilter/xt_AUDIT.c >> >> > @@ -31,146 +31,78 @@ MODULE_ALIAS("ip6t_AUDIT"); >> >> >> >> ... >> >> >> >> > -static void audit_ip4(struct audit_buffer *ab, struct sk_buff *skb) >> >> > +static bool audit_ip4(struct audit_buffer *ab, struct sk_buff *skb) >> >> > { >> >> > struct iphdr _iph; >> >> > const struct iphdr *ih; >> >> > >> >> > ih = skb_header_pointer(skb, 0, sizeof(_iph), &_iph); >> >> >> >> It seems like we should be using skb_network_offset(skb) instead of 0 >> >> above, yes? Granted, this isn't new, but let's fix it. >> > >> > Yes, I agree. How does this even work now? Maybe the MAC header hasn't >> > been added yet (or has already been processed and stripped off) so that >> > skb->data is already pointing at the network header and hence has an >> > offset of 0. Can you be more explicit and elaborate to say if this what >> > you were thinking? >> >> Unfortunately, not really, I haven't thought through of all the >> situations and it has been a long time since I've had to worry about >> things like this. I think we are in agreement that it needs to >> change, so let's just make the change. > > Given Pablo's assurances, this could go either way, fix audit_ip4 to use > skb_network_offset() or fix audit_ip6 to use zero. I don't have a > strong opinion, but using zero would be more efficient while using > skb_network_offset() would remove the doubt. Either way, the > consistency will avoid raising doubt in the future as you have > (rightfully) done. Just use skb_network_offset() as it is the safer option and there is plenty of precedence. Considering that we expect NETFILTER_PKT to see limited use, I'm more concerned about it not breaking than some small loss of performance.

>> >> > static unsigned int >> >> > audit_tg(struct sk_buff *skb, const struct xt_action_param *par) >> >> > { >> >> > - const struct xt_audit_info *info = par->targinfo; >> >> > struct audit_buffer *ab; >> >> > + int fam = -1; >> >> > >> >> > if (audit_enabled == 0) >> >> > goto errout; >> >> > - >> >> > ab = audit_log_start(NULL, GFP_ATOMIC, AUDIT_NETFILTER_PKT); >> >> > if (ab == NULL) >> >> > goto errout; >> >> > >> >> > - audit_log_format(ab, "action=%hhu hook=%u len=%u inif=%s outif=%s", >> >> > - info->type, par->hooknum, skb->len, >> >> > - par->in ? par->in->name : "?", >> >> > - par->out ? par->out->name : "?"); >> >> > - >> >> > - if (skb->mark) >> >> > - audit_log_format(ab, " mark=%#x", skb->mark); >> >> > - >> >> > - if (skb->dev && skb->dev->type == ARPHRD_ETHER) { >> >> > - audit_log_format(ab, " smac=%pM dmac=%pM macproto=0x%04x", >> >> > - eth_hdr(skb)->h_source, eth_hdr(skb)->h_dest, >> >> > - ntohs(eth_hdr(skb)->h_proto)); >> >> > + audit_log_format(ab, "mark=%#x", skb->mark ?: -1); >> >> >> >> How do Steve's userspace tools like the unset/-1 value represented >> >> when it is a hex value: -1 or 0xffffffff? >> > >> > My understanding is they are set up to cope with this. >> >> How does userspace distinguish between an unset nfmark and a nfmark of >> 0xffffffff? > > It never had to deal specifically with nfmark previously because it > wasn't included if it was blank. Generally other values that are -1 are > interpreted by the audit userspace tools as unset (session id, auid, > etc...) Yes, I know, let me get straight to the point: should we use "mark=-1" when the nfmark is unset instead of "mark=0xffffffff"?

paul moore