_rt6i_peer is no longer needed after the last patch,
'ipv6: Stop rt6_info from using inet_peer's metrics'.

DST_METRICS_FORCE_OVERWRITE is added by
commit e5fd387a ("ipv6: do not overwrite inetpeer metrics prematurely").
Since inetpeer is no longer used for metrics, this bit is also not needed.
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Reviewed-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Michal Kubeček <mkubecek@suse.cz>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

inet_peer is indexed by the dst address alone.  However, the fib6 tree
could have multiple routing entries (rt6_info) for the same dst. For
example,
1. A /128 dst via multiple gateways.
2. A RTF_CACHE route cloned from a /128 route.

In the above cases, all of them will share the same metrics and
step on each other.

This patch will steer away from inet_peer's metrics and use
dst_cow_metrics_generic() for everything.

Change Highlights:
1. Remove rt6_cow_metrics() which currently acquires metrics from
   inet_peer for DST_HOST route (i.e. /128 route).
2. Add rt6i_pmtu to take care of the pmtu update to avoid creating a
   full size metrics just to override the RTAX_MTU.
3. After (2), the RTF_CACHE route can also share the metrics with its
   dst.from route, by:
   dst_init_metrics(&cache_rt->dst, dst_metrics_ptr(cache_rt->dst.from), true);
4. Stop creating RTF_CACHE route by cloning another RTF_CACHE route.  Instead,
   directly clone from rt->dst.

   [ Currently, cloning from another RTF_CACHE is only possible during
     rt6_do_redirect().  Also, the old clone is removed from the tree
     immediately after the new clone is added. ]

   In case of cloning from an older redirect RTF_CACHE, it should work as
   before.

   In case of cloning from an older pmtu RTF_CACHE, this patch will forget
   the pmtu and re-learn it (if there is any) from the redirected route.

The _rt6i_peer and DST_METRICS_FORCE_OVERWRITE will be removed
in the next cleanup patch.
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Reviewed-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Do the nla validation earlier, outside the write lock.

This is needed by followup patch which needs to be able to call
request_module (which can sleep) if needed.

Joint work with Daniel Borkmann.
Signed-off-by: NDaniel Borkmann <dborkman@redhat.com>
Signed-off-by: NFlorian Westphal <fw@strlen.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Cc: YOSHIFUJI Hideaki <hideaki@yoshifuji.org>
Cc: Martin Lau <kafai@fb.com>
Signed-off-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Also renamed struct fib6_walker_t to fib6_walker and enum fib_walk_state_t
to fib6_walk_state as recommended by Cong Wang.

Cc: Cong Wang <cwang@twopensource.com>
Cc: YOSHIFUJI Hideaki <hideaki@yoshifuji.org>
Cc: Martin Lau <kafai@fb.com>
Signed-off-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Eric Dumazet noticed that all no-nonexthop or no-gateway routes which
are already marked DST_HOST (e.g. input routes routes) will always be
invalidated during sk_dst_check. Thus per-socket dst caching absolutely
had no effect and early demuxing had no effect.

Thus this patch removes rt6i_genid: fn_sernum already gets modified during
add operations, so we only must ensure we mutate fn_sernum during ipv6
address remove operations. This is a fairly cost extensive operations,
but address removal should not happen that often. Also our mtu update
functions do the same and we heard no complains so far. xfrm policy
changes also cause a call into fib6_flush_trees. Also plug a hole in
rt6_info (no cacheline changes).

I verified via tracing that this change has effect.

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: YOSHIFUJI Hideaki <hideaki@yoshifuji.org>
Cc: Vlad Yasevich <vyasevich@gmail.com>
Cc: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Cc: Martin Lau <kafai@fb.com>
Signed-off-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

If an IPv6 host route with metrics exists, an attempt to add a
new route for the same target with different metrics fails but
rewrites the metrics anyway:

12sp0:~ # ip route add fec0::1 dev eth0 rto_min 1000
12sp0:~ # ip -6 route show
fe80::/64 dev eth0  proto kernel  metric 256
fec0::1 dev eth0  metric 1024  rto_min lock 1s
12sp0:~ # ip route add fec0::1 dev eth0 rto_min 1500
RTNETLINK answers: File exists
12sp0:~ # ip -6 route show
fe80::/64 dev eth0  proto kernel  metric 256
fec0::1 dev eth0  metric 1024  rto_min lock 1.5s

This is caused by all IPv6 host routes using the metrics in
their inetpeer (or the shared default). This also holds for the
new route created in ip6_route_add() which shares the metrics
with the already existing route and thus ip6_route_add()
rewrites the metrics even if the new route ends up not being
used at all.

Another problem is that old metrics in inetpeer can reappear
unexpectedly for a new route, e.g.

12sp0:~ # ip route add fec0::1 dev eth0 rto_min 1000
12sp0:~ # ip route del fec0::1
12sp0:~ # ip route add fec0::1 dev eth0
12sp0:~ # ip route change fec0::1 dev eth0 hoplimit 10
12sp0:~ # ip -6 route show
fe80::/64 dev eth0  proto kernel  metric 256
fec0::1 dev eth0  metric 1024  hoplimit 10 rto_min lock 1s

Resolve the first problem by moving the setting of metrics down
into fib6_add_rt2node() to the point we are sure we are
inserting the new route into the tree. Second problem is
addressed by introducing new flag DST_METRICS_FORCE_OVERWRITE
which is set for a new host route in ip6_route_add() and makes
ipv6_cow_metrics() always overwrite the metrics in inetpeer
(even if they are not "new"); it is reset after that.

v5: use a flag in _metrics member rather than one in flags

v4: fix a typo making a condition always true (thanks to Hannes
Frederic Sowa)

v3: rewritten based on David Miller's idea to move setting the
metrics (and allocation in non-host case) down to the point we
already know the route is to be inserted. Also rebased to
net-next as it is quite late in the cycle.
Signed-off-by: NMichal Kubecek <mkubecek@suse.cz>
Acked-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

since the prune parameter for fib6_clean_all always is 0, remove it.
Signed-off-by: NLi RongQing <roy.qing.li@gmail.com>
Acked-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

On receiving a packet too big icmp error we update the expire value by
calling rt6_update_expires. This function uses dst_set_expires which is
implemented that it can only reduce the expiration value of the dst entry.

If we insert new routing non-expiry information into the ipv6 fib where
we already have a matching rt6_info we only clear the RTF_EXPIRES flag
in rt6i_flags and leave the dst.expires value as is.

When new mtu information arrives for that cached dst_entry we again
call dst_set_expires. This time it won't update the dst.expire value
because we left the dst.expire value intact from the last update. So
dst_set_expires won't touch dst.expires.

Fix this by resetting dst.expires when clearing the RTF_EXPIRE flag.
dst_set_expires checks for a zero expiration and updates the
dst.expires.

In the past this (not updating dst.expires) was necessary because
dst.expire was placed in a union with the dst_entry *from reference
and rt6_clean_expires did assign NULL to it. This split happend in
ecd98837 ("ipv6: fix race condition
regarding dst->expires and dst->from").
Reported-by: NSteinar H. Gunderson <sgunderson@bigfoot.com>
Reported-by: NValentijn Sessink <valentyn@blub.net>
Cc: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Acked-by: NEric Dumazet <edumazet@google.com>
Tested-by: NValentijn Sessink <valentyn@blub.net>
Signed-off-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Dumping routes on a system with lots rt6_infos in the fibs causes up to
11-order allocations in seq_file (which fail). While we could switch
there to vmalloc we could just implement the streaming interface for
/proc/net/ipv6_route. This patch switches /proc/net/ipv6_route from
single_open_net to seq_open_net.

loff_t *pos tracks dst entries.

Also kill never used struct rt6_proc_arg and now unused function
fib6_clean_all_ro.

Cc: Ben Greear <greearb@candelatech.com>
Cc: Patrick McHardy <kaber@trash.net>
Cc: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

There are a mix of function prototypes with and without extern
in the kernel sources.  Standardize on not using extern for
function prototypes.

Function prototypes don't need to be written with extern.
extern is assumed by the compiler.  Its use is as unnecessary as
using auto to declare automatic/local variables in a block.
Signed-off-by: NJoe Perches <joe@perches.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

On a high-traffic router with many processors and many IPv6 dst
entries, soft lockup in fib6_run_gc() can occur when number of
entries reaches gc_thresh.

This happens because fib6_run_gc() uses fib6_gc_lock to allow
only one thread to run the garbage collector but ip6_dst_gc()
doesn't update net->ipv6.ip6_rt_last_gc until fib6_run_gc()
returns. On a system with many entries, this can take some time
so that in the meantime, other threads pass the tests in
ip6_dst_gc() (ip6_rt_last_gc is still not updated) and wait for
the lock. They then have to run the garbage collector one after
another which blocks them for quite long.

Resolve this by replacing special value ~0UL of expire parameter
to fib6_run_gc() by explicit "force" parameter to choose between
spin_lock_bh() and spin_trylock_bh() and call fib6_run_gc() with
force=false if gc_thresh is reached but not max_size.
Signed-off-by: NMichal Kubecek <mkubecek@suse.cz>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Eric Dumazet wrote:
| Some strange crashes happen in rt6_check_expired(), with access
| to random addresses.
|
| At first glance, it looks like the RTF_EXPIRES and
| stuff added in commit 1716a961
| (ipv6: fix problem with expired dst cache)
| are racy : same dst could be manipulated at the same time
| on different cpus.
|
| At some point, our stack believes rt->dst.from contains a dst pointer,
| while its really a jiffie value (as rt->dst.expires shares the same area
| of memory)
|
| rt6_update_expires() should be fixed, or am I missing something ?
|
| CC Neil because of https://bugzilla.redhat.com/show_bug.cgi?id=892060

Because we do not have any locks for dst_entry, we cannot change
essential structure in the entry; e.g., we cannot change reference
to other entity.

To fix this issue, split 'from' and 'expires' field in dst_entry
out of union.  Once it is 'from' is assigned in the constructor,
keep the reference until the very last stage of the life time of
the object.

Of course, it is unsafe to change 'from', so make rt6_set_from simple
just for fresh entries.
Reported-by: NEric Dumazet <eric.dumazet@gmail.com>
Reported-by: NNeil Horman <nhorman@tuxdriver.com>
CC: Gao Feng <gaofeng@cn.fujitsu.com>
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Reviewed-by: NEric Dumazet <edumazet@google.com>
Reported-by: NSteinar H. Gunderson <sesse@google.com>
Reviewed-by: NNeil Horman <nhorman@tuxdriver.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

CC: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

6431cbc2(Create a mechanism for upward inetpeer propagation into routes)
introduces these codes, but this mechanism is never enabled since
rt6i_peer_genid always is zero whether it is not assigned or assigned by
rt6_peer_genid(). After 5943634f (ipv4: Maintain redirect and PMTU info
in struct rtable again), the ipv4 related codes of this mechanism has been
removed, I think we maybe able to remove them now.
Signed-off-by: NLi RongQing <roy.qing.li@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

As suggested by Eric, we could introduce a helper function
for ipv6 too, to avoid checking if rt is NULL before
dst_release().

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: NCong Wang <amwang@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Each nexthop is added like a single route in the routing table. All routes
that have the same metric/weight and destination but not the same gateway
are considering as ECMP routes. They are linked together, through a list called
rt6i_siblings.

ECMP routes can be added in one shot, with RTA_MULTIPATH attribute or one after
the other (in both case, the flag NLM_F_EXCL should not be set).

The patch is based on a previous work from
Luc Saillard <luc.saillard@6wind.com>.
Signed-off-by: NNicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

IPv6 dst should take care of rt_genid too. When a xfrm policy is inserted or
deleted, all dst should be invalidated.
To force the validation, dst entries should be created with ->obsolete set to
DST_OBSOLETE_FORCE_CHK. This was already the case for all functions calling
ip6_dst_alloc(), except for ip6_rt_copy().

As a consequence, we can remove the specific code in inet6_connection_sock.
Signed-off-by: NNicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

When adding a blackhole or a prohibit route, they were handling like classic
routes. Moreover, it was only possible to add this kind of routes by specifying
an interface.

Bug already reported here:
  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=498498

Before the patch:
  $ ip route add blackhole 2001::1/128
  RTNETLINK answers: No such device
  $ ip route add blackhole 2001::1/128 dev eth0
  $ ip -6 route | grep 2001
  2001::1 dev eth0  metric 1024

After:
  $ ip route add blackhole 2001::1/128
  $ ip -6 route | grep 2001
  blackhole 2001::1 dev lo  metric 1024  error -22

v2: wrong patch
v3: add a field fc_type in struct fib6_config to store RTN_* type
Signed-off-by: NNicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This makes for a simplified conversion away from dst_get_neighbour*().

All code outside of ipv6 will use neigh lookups via dst_neigh_lookup*().
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This reverts commit 2a0c451a.

It causes crashes, because now ip6_null_entry is used before
it is initialized.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

/proc/net/ipv6_route reflects the contents of fib_table_hash. The proc
handler is installed in ip6_route_net_init() whereas fib_table_hash is
allocated in fib6_net_init() _after_ the proc handler has been installed.

This opens up a short time frame to access fib_table_hash with its pants
down.

fib6_init() as a whole can't be moved to an earlier position as it also
registers the rtnetlink message handlers which should be registered at
the end. Therefore split it into fib6_init() which is run early and
fib6_init_late() to register the rtnetlink message handlers.
Signed-off-by: NThomas Graf <tgraf@suug.ch>
Reviewed-by: NNeil Horman <nhorman@tuxdriver.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NDavid S. Miller <davem@davemloft.net>

We encode the pointer(s) into an unsigned long with one state bit.

The state bit is used so we can store the inetpeer tree root to use
when resolving the peer later.

Later the peer roots will be per-FIB table, and this change works to
facilitate that.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Functionally, this change is a NOP.

Semantically, rt6_clean_expires() wants to do rt->dst.from = NULL instead of
rt->dst.expires = 0. It is clearing the RTF_EXPIRES flag, so the union is going
to be treated as a pointer (dst.from) not a long (dst.expires).
Signed-off-by: NJiri Bohac <jbohac@suse.cz>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Commit 1716a961 (ipv6: fix problem with expired dst cache) broke PMTU
discovery. rt6_update_expires() calls dst_set_expires(), which only updates
dst->expires if it has not been set previously (expires == 0) or if the new
expires is earlier than the current dst->expires.

rt6_update_expires() needs to zero rt->dst.expires, otherwise it will contain
ivalid data left over from rt->dst.from and will confuse dst_set_expires().
Signed-off-by: NJiri Bohac <jbohac@suse.cz>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

If the ipv6 dst cache which copy from the dst generated by ICMPV6 RA packet.
this dst cache will not check expire because it has no RTF_EXPIRES flag.
So this dst cache will always be used until the dst gc run.

Change the struct dst_entry,add a union contains new pointer from and expires.
When rt6_info.rt6i_flags has no RTF_EXPIRES flag,the dst.expires has no use.
we can use this field to point to where the dst cache copy from.
The dst.from is only used in IPV6.

rt6_check_expired check if rt6_info.dst.from is expired.

ip6_rt_copy only set dst.from when the ort has flag RTF_ADDRCONF
and RTF_DEFAULT.then hold the ort.

ip6_dst_destroy release the ort.

Add some functions to operate the RTF_EXPIRES flag and expires(from) together.
and change the code to use these new adding functions.

Changes from v5:
modify ip6_route_add and ndisc_router_discovery to use new adding functions.

Only set dst.from when the ort has flag RTF_ADDRCONF
and RTF_DEFAULT.then hold the ort.
Signed-off-by: NGao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

During some debugging I needed to look into how /proc/net/ipv6_route
operated and in my digging I found its calling fib6_clean_all() which uses
"write_lock_bh(&table->tb6_lock)" before doing the walk of the table. I
found this on 2.6.32, but reading the code I believe the same basic idea
exists currently. Looking at the rtnetlink code they are only calling
"read_lock_bh(&table->tb6_lock);" via fib6_dump_table(). While I realize
reading from proc isn't the recommended way of fetching the ipv6 route
table; taking a write lock seems unnecessary and would probably cause
network performance issues.

To verify this I loaded up the ipv6 route table and then ran iperf in 3
cases:
  * doing nothing
  * reading ipv6 route table via proc
    (while :; do cat /proc/net/ipv6_route > /dev/null; done)
  * reading ipv6 route table via rtnetlink
    (while :; do ip -6 route show table all > /dev/null; done)

* Load the ipv6 route table up with:
  * for ((i = 0;i < 4000;i++)); do ip route add unreachable 2000::$i; done

* iperf commands:
  * client: iperf -i 1 -V -c <ipv6 addr>
  * server: iperf -V -s

* iperf results - 3 runs each (in Mbits/sec)
  * nothing: client: 927,927,927 server: 927,927,927
  * proc: client: 179,97,96,113 server: 142,112,133
  * iproute: client: 928,927,928 server: 927,927,927

lock_stat shows taking the write lock is causing the slowdown. Using this
info I decided to write a version of fib6_clean_all() which replaces
write_lock_bh(&table->tb6_lock) with read_lock_bh(&table->tb6_lock). With
this new function I see the same results as with my rtnetlink iperf test.
Signed-off-by: NJosh Hunt <joshhunt00@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

It just obscures that the netdevice pointer and the expires value are
implemented in the dst_entry sub-object of the ipv6 route.

And it makes grepping for dst_entry member uses much harder too.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

It just makes it harder to see 1) what the code is doing
and 2) grep for all users of dst{->,.}neighbour
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

These header files are never installed to user consumption, so any
__KERNEL__ cpp checks are superfluous.

Projects should also not copy these files into their userland utility
sources and try to use them there.  If they insist on doing so, the
onus is on them to sanitize the headers as needed.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Add const qualifiers to structs iphdr, ipv6hdr and in6_addr pointers
where possible, to make code intention more obvious.
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

[ipv6] Add support for RTA_PREFSRC

This patch allows a user to select the preferred source address
for a specific IPv6-Route. It can be set via a netlink message
setting RTA_PREFSRC to a valid IPv6 address which must be
up on the device the route will be bound to.
Signed-off-by: NDaniel Walter <dwalter@barracuda.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NDavid S. Miller <davem@davemloft.net>

If we didn't have a routing cache, we would not be able to properly
propagate certain kinds of dynamic path attributes, for example
PMTU information and redirects.

The reason is that if we didn't have a routing cache, then there would
be no way to lookup all of the active cached routes hanging off of
sockets, tunnels, IPSEC bundles, etc.

Consider the case where we created a cached route, but no inetpeer
entry existed and also we were not asked to pre-COW the route metrics
and therefore did not force the creation a new inetpeer entry.

If we later get a PMTU message, or a redirect, and store this
information in a new inetpeer entry, there is no way to teach that
cached route about the newly existing inetpeer entry.

The facilities implemented here handle this problem.

First we create a generation ID.  When we create a cached route of any
kind, we remember the generation ID at the time of attachment.  Any
time we force-create an inetpeer entry in response to new path
information, we bump that generation ID.

The dst_ops->check() callback is where the knowledge of this event
is propagated.  If the global generation ID does not equal the one
stored in the cached route, and the cached route has not attached
to an inetpeer yet, we look it up and attach if one is found.  Now
that we've updated the cached route's information, we update the
route's generation ID too.

This clears the way for implementing PMTU and redirects directly in
the inetpeer cache.  There is absolutely no need to consult cached
route information in order to maintain this information.

At this point nothing bumps the inetpeer genids, that comes in the
later changes which handle PMTUs and redirects using inetpeers.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

They are only allowed on cached ipv6 routes.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

remove useless union keyword in rtable, rt6_info and dn_route.

Since there is only one member in a union, the union keyword isn't useful.
Signed-off-by: NChangli Gao <xiaosuo@gmail.com>
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The head element of rt6_info{} is dst_entry{}, and
IPv6 specific elements follow.

Because elements at the end of dst_entry{} are frequently
updated, it is not good to put frequently-used static
elements, such as rt6i_idev, rt6i_dst or rt6i_flags in the
same cache line.

On the other hand, fib6_table, rt6i_node or rt6i_gateway are
rarely used, so it is okay to stay in the same cache line.

Let's rearrange rt6_info{}.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

When the fib size exceeds what can be dumped in a single skb, the
dump is suspended and resumed once the last skb has been received
by userspace. When the fib is changed while the dump is suspended,
the walker might contain stale pointers, causing a crash when the
dump is resumed.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
IP: [<ffffffffa01bce04>] fib6_walk_continue+0xbb/0x124 [ipv6]
PGD 5347a067 PUD 65c7067 PMD 0
Oops: 0000 [#1] PREEMPT SMP
...
RIP: 0010:[<ffffffffa01bce04>]
[<ffffffffa01bce04>] fib6_walk_continue+0xbb/0x124 [ipv6]
...
Call Trace:
 [<ffffffff8104aca3>] ? mutex_spin_on_owner+0x59/0x71
 [<ffffffffa01bd105>] inet6_dump_fib+0x11b/0x1b9 [ipv6]
 [<ffffffff81371af4>] netlink_dump+0x5b/0x19e
 [<ffffffff8134f288>] ? consume_skb+0x28/0x2a
 [<ffffffff81373b69>] netlink_recvmsg+0x1ab/0x2c6
 [<ffffffff81372781>] ? netlink_unicast+0xfa/0x151
 [<ffffffff813483e0>] __sock_recvmsg+0x6d/0x79
 [<ffffffff81348a53>] sock_recvmsg+0xca/0xe3
 [<ffffffff81066d4b>] ? autoremove_wake_function+0x0/0x38
 [<ffffffff811ed1f8>] ? radix_tree_lookup_slot+0xe/0x10
 [<ffffffff810b3ed7>] ? find_get_page+0x90/0xa5
 [<ffffffff810b5dc5>] ? filemap_fault+0x201/0x34f
 [<ffffffff810ef152>] ? fget_light+0x2f/0xac
 [<ffffffff813519e7>] ? verify_iovec+0x4f/0x94
 [<ffffffff81349a65>] sys_recvmsg+0x14d/0x223

Store the serial number when beginning to walk the fib and reload
pointers when continuing to walk after a change occured. Similar
to other dumping functions, this might cause unrelated entries to
be missed when entries are deleted.
Tested-by: NBen Greear <greearb@candelatech.com>
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>