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Hannes Frederic Sowa df4d92549f ipv4: try to cache dst_entries which would cause a redirect 
Not caching dst_entries which cause redirects could be exploited by hosts
on the same subnet, causing a severe DoS attack. This effect aggravated
since commit f886497212 ("ipv4: fix dst race in sk_dst_get()").

Lookups causing redirects will be allocated with DST_NOCACHE set which
will force dst_release to free them via RCU.  Unfortunately waiting for
RCU grace period just takes too long, we can end up with >1M dst_entries
waiting to be released and the system will run OOM. rcuos threads cannot
catch up under high softirq load.

Attaching the flag to emit a redirect later on to the specific skb allows
us to cache those dst_entries thus reducing the pressure on allocation
and deallocation.

This issue was discovered by Marcelo Leitner.

Cc: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Marcelo Leitner <mleitner@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>
2015-01-26 17:28:27 -08:00
..
acpi ACPI / processor: Convert apic_id to phys_id to make it arch agnostic 2015-01-05 23:32:42 +01:00
asm-generic mm: mmu_gather: use tlb->end != 0 only for TLB invalidation 2015-01-13 15:20:40 +13:00
clocksource
crypto
drm Revert "drm/gem: Warn on illegal use of the dumb buffer interface v2" 2014-12-24 13:13:22 +10:00
dt-bindings Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/evalenti/linux-soc-thermal into thermal-soc 2014-12-21 22:49:12 +08:00
keys
kvm
linux Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2015-01-20 18:19:31 +12:00
math-emu
media
memory
misc
net ipv4: try to cache dst_entries which would cause a redirect 2015-01-26 17:28:27 -08:00
pcmcia
ras
rdma
rxrpc
scsi SCSI for-linus on 20141220 2014-12-20 13:42:57 -08:00
soc
sound ALSA: pcm: Fix kerneldoc for params_*() functions 2014-12-30 16:41:11 +01:00
target target: Drop left-over fabric_max_sectors attribute 2015-01-09 15:22:05 -08:00
trace SCSI for-linus on 20141220 2014-12-20 13:42:57 -08:00
uapi Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2015-01-20 18:19:31 +12:00
video
xen x86/xen: properly retrieve NMI reason 2015-01-13 09:39:50 +00:00
Kbuild