diff mbox

kernel v4.8: iptables logs are truncated with the 4.8 kernel?

Message ID CAML_gOeUOrt=-D3VHS2B3B_Q1F2-DAYK95Oxu4FEvfE43hjb3g@mail.gmail.com
State Awaiting Upstream, archived
Delegated to: David Miller
Headers show

Commit Message

Liping Zhang Oct. 10, 2016, 12:21 p.m. UTC 
Hi Chris,

2016-10-10 15:02 GMT+08:00 Chris Caputo <ccaputo@alt.net>:
> On Tue, 4 Oct 2016, Justin Piszcz wrote:
>> kernel 4.8 with ulogd-2.0.5- IPs are no longer logged:
>>
>> Oct  4 17:51:30 atom INPUT_BLOCK IN=eth1 OUT=
>> MAC=00:1b:21:9c:3b:fa:3e:94:d5:d2:49:1e:08:00 LEN=0 TOS=00 PREC=0x00
>> TTL=0 ID=0 PROTO=0 MARK=0
>> Oct  4 17:51:31 atom INPUT_BLOCK IN=eth1 OUT=
>> MAC=00:1b:21:9c:3b:fa:3e:94:d5:d2:49:1e:08:00 LEN=0 TOS=00 PREC=0x00
>> TTL=0 ID=0 PROTO=0 MARK=0
>> Oct  4 17:51:32 atom INPUT_BLOCK IN=eth1 OUT=
>> MAC=00:1b:21:9c:3b:fa:3e:94:d5:d2:49:1e:08:00 LEN=0 TOS=00 PREC=0x00
>> TTL=0 ID=0 PROTO=0 MARK=0
>>
>> (reboot back to kernel 4.7, works fine)
>>
>> kernel 4.7 with ulogd-2.0.5:
>> Oct  4 17:56:44 atom INPUT_BLOCK IN=eth1 OUT=
>> MAC=00:1b:21:9c:3b:fa:3e:94:d5:d2:49:1e:08:00 SRC=74.125.22.125
>> DST=1.2.3.4 LEN=397 TOS=00 PREC=0x00 TTL=48 ID=58093 PROTO=TCP
>> SPT=5222 DPT=19804 SEQ=2032644254 ACK=2273184383 WINDOW=55272 ACK PSH
>> URGP=0 MARK=0
>> Oct  4 17:56:45 atom INPUT_BLOCK IN=eth1 OUT=
>> MAC=00:1b:21:9c:3b:fa:3e:94:d5:d2:49:1e:08:00 SRC=74.125.22.125
>> DST=1.2.3.4 LEN=397 TOS=00 PREC=0x00 TTL=48 ID=58725 PROTO=TCP
>> SPT=5222 DPT=19804 SEQ=2032644254 ACK=2273184383 WINDOW=55272 ACK PSH
>> URGP=0 MARK=0
>>
>> Looks like there were some changes in the 4.8 kernel regarding ulogd,
>> has anyone else run into this problem?
>
> For me, kernel 4.8.1 results in segfaults in ulogd-2.0.5 at:
>
>   Program received signal SIGSEGV, Segmentation fault.
>   0x00007ffff65fd18a in _interp_iphdr (pi=0x617f50, len=0) at ulogd_raw2packet_BASE.c:720
>
>   715     static int _interp_iphdr(struct ulogd_pluginstance *pi, uint32_t len)
>   716     {
>   717             struct ulogd_key *ret = pi->output.keys;
>   718             struct iphdr *iph =
>   719                     ikey_get_ptr(&pi->input.keys[INKEY_RAW_PCKT]);
>   720             void *nexthdr = (uint32_t *)iph + iph->ihl;
>
> I believe 7643507fe8b5bd8ab7522f6a81058cc1209d2585 changed previous
> behavior by not always copying IP header data to user space.
>
> On my machine IPv4 log packets result in a ulogd segfault while IPv6
> packets do not.  I'm not sure of the cause of the difference.
>
> The corresponding userspace commit for the 209d2585 kernel change is:
>
>   https://git.netfilter.org/iptables/commit/?id=7070b1f3c88a0c3d4e315c00cca61f05b0fbc882
>
> This adds --nflog-size to iptables.  When --nflog-size is used with my
> iptables NFLOG lines, the ulogd-2.0.5 segfaults cease.

What numbers did you specify after --nflog-size option?
--nflog-size 0 or ...? If you want log the whole packet to
the ulogd, please do not specify this nflog-size option.

>
> I'm surprised to see a kernel change cause unexpected userspace segfaults,
> so further investigation into a kernel fix would seem a good idea.

According to the original user's manual, nflog-range option was
designed to be the number of bytes copied to userspace, but
unfortunately there's a bug from the beginning and it never works,
i.e. in kernel, it just ignored this option.

Try to change the current nflog-range option's semantics may
cause unexpected results(maybe like this ulogd crash) ...

In order to keep compatibility, Vishwanath introduce a new
nflog-size option and keep nflog-range unchanged. If you just
upgrade the kernel, and do not change iptables rules, this
problem will not happen.

So I think this is ulogd's bug, in _interp_iphdr, it try to
dereference the iphdr pointer before validation check, meanwhile
this problem does not exist in ipv6 path.  Can you try this patch:

                return ULOGD_IRET_OK;
@@ -734,6 +734,7 @@ static int _interp_iphdr(struct ulogd_pluginstance
*pi, uint32_t len)
        okey_set_u16(&ret[KEY_IP_ID], ntohs(iph->id));
        okey_set_u16(&ret[KEY_IP_FRAGOFF], ntohs(iph->frag_off));

+       nexthdr = (uint32_t *)iph + iph->ihl;
        switch (iph->protocol) {
        case IPPROTO_TCP:
                _interp_tcp(pi, nexthdr, len);

Thanks

> Having to add the likes of "--nflog-size 200" (200 simply being what I am
> using) to every NFLOG line in firewall configs is a significant burden for
> many.
>
> Putting out a new release of iptables may help ease this transition if the
> kernel is not patched to fix this.  I had to use the git code since 1.6.0
> doesn't have it.
>
> Chris

Comments

Chris Caputo Oct. 10, 2016, 6:33 p.m. UTC | #1 
On Mon, 10 Oct 2016, Liping Zhang wrote:
> 2016-10-10 15:02 GMT+08:00 Chris Caputo <ccaputo@alt.net>:
> >   Program received signal SIGSEGV, Segmentation fault.
> >   0x00007ffff65fd18a in _interp_iphdr (pi=0x617f50, len=0) at ulogd_raw2packet_BASE.c:720
> >
> >   715     static int _interp_iphdr(struct ulogd_pluginstance *pi, uint32_t len)
> >   716     {
> >   717             struct ulogd_key *ret = pi->output.keys;
> >   718             struct iphdr *iph =
> >   719                     ikey_get_ptr(&pi->input.keys[INKEY_RAW_PCKT]);
> >   720             void *nexthdr = (uint32_t *)iph + iph->ihl;
> >
> > I believe 7643507fe8b5bd8ab7522f6a81058cc1209d2585 changed previous
> > behavior by not always copying IP header data to user space.
> >
> > On my machine IPv4 log packets result in a ulogd segfault while IPv6
> > packets do not.  I'm not sure of the cause of the difference.
> >
> > The corresponding userspace commit for the 209d2585 kernel change is:
> >
> >   https://git.netfilter.org/iptables/commit/?id=7070b1f3c88a0c3d4e315c00cca61f05b0fbc882
> >
> > This adds --nflog-size to iptables.  When --nflog-size is used with my
> > iptables NFLOG lines, the ulogd-2.0.5 segfaults cease.
> 
> What numbers did you specify after --nflog-size option?
> --nflog-size 0 or ...? If you want log the whole packet to
> the ulogd, please do not specify this nflog-size option.

Not specifying nflog-size does not appear to log the whole packet...

If "--nflog-size" is unspecified, and the iptables config is left 
unchanged when the kernel is upgraded to 4.8, ulogd-2.0.5 crashes.

If "--nflog-size 0" is used, ulogd-2.0.5 crashes.

If "--nflog-size" is used with size 1 or greater, ulogd-2.0.5 is fine.

> > I'm surprised to see a kernel change cause unexpected userspace segfaults,
> > so further investigation into a kernel fix would seem a good idea.
> 
> According to the original user's manual, nflog-range option was
> designed to be the number of bytes copied to userspace, but
> unfortunately there's a bug from the beginning and it never works,
> i.e. in kernel, it just ignored this option.
> 
> Try to change the current nflog-range option's semantics may
> cause unexpected results(maybe like this ulogd crash) ...
> 
> In order to keep compatibility, Vishwanath introduce a new
> nflog-size option and keep nflog-range unchanged. If you just
> upgrade the kernel, and do not change iptables rules, this
> problem will not happen.

I am reporting that the problem does happen simply with an upgrade to 
kernel 4.8 and no other changes.  When "--nflog-size" is unspecified or 
set to 0, the bug in ulogd-2.0.5 gets triggered.

I agree there is a bug in ulogd-2.0.5 that this kernel change exposed, but 
I am trying to explain that all ulogd users risk this segfault if they 
upgrade to kernel 4.8 and don't either update to a fixed ulogd (possibly 
using your patch below) or an unreleased iptables with iptables config 
changes to implement nflog-size on each NFLOG target.

> So I think this is ulogd's bug, in _interp_iphdr, it try to
> dereference the iphdr pointer before validation check, meanwhile
> this problem does not exist in ipv6 path.  Can you try this patch:
> 
> diff --git a/filter/raw2packet/ulogd_raw2packet_BASE.c
> b/filter/raw2packet/ulogd_raw2packet_BASE.c
> index 8a6180c..fd2665a 100644
> --- a/filter/raw2packet/ulogd_raw2packet_BASE.c
> +++ b/filter/raw2packet/ulogd_raw2packet_BASE.c
> @@ -717,7 +717,7 @@ static int _interp_iphdr(struct ulogd_pluginstance
> *pi, uint32_t len)
>         struct ulogd_key *ret = pi->output.keys;
>         struct iphdr *iph =
>                 ikey_get_ptr(&pi->input.keys[INKEY_RAW_PCKT]);
> -       void *nexthdr = (uint32_t *)iph + iph->ihl;
> +       void *nexthdr;
> 
>         if (len < sizeof(struct iphdr) || len <= (uint32_t)(iph->ihl * 4))
>                 return ULOGD_IRET_OK;
> @@ -734,6 +734,7 @@ static int _interp_iphdr(struct ulogd_pluginstance
> *pi, uint32_t len)
>         okey_set_u16(&ret[KEY_IP_ID], ntohs(iph->id));
>         okey_set_u16(&ret[KEY_IP_FRAGOFF], ntohs(iph->frag_off));
> 
> +       nexthdr = (uint32_t *)iph + iph->ihl;
>         switch (iph->protocol) {
>         case IPPROTO_TCP:
>                 _interp_tcp(pi, nexthdr, len);

I agree this will likely fix ulogd, but this misses the point about the 
new kernel defaulting to a zero size return when it used to return the 
packet.

Thanks,
Chris
diff mbox

Patch

diff --git a/filter/raw2packet/ulogd_raw2packet_BASE.c
b/filter/raw2packet/ulogd_raw2packet_BASE.c
index 8a6180c..fd2665a 100644
--- a/filter/raw2packet/ulogd_raw2packet_BASE.c
+++ b/filter/raw2packet/ulogd_raw2packet_BASE.c
@@ -717,7 +717,7 @@  static int _interp_iphdr(struct ulogd_pluginstance
*pi, uint32_t len)
        struct ulogd_key *ret = pi->output.keys;
        struct iphdr *iph =
                ikey_get_ptr(&pi->input.keys[INKEY_RAW_PCKT]);
-       void *nexthdr = (uint32_t *)iph + iph->ihl;
+       void *nexthdr;

        if (len < sizeof(struct iphdr) || len <= (uint32_t)(iph->ihl * 4))