Re: [PATCH] netfilter/x_tables: do not fail xt_alloc_table_info too easilly

[Michal Hocko <mhocko@kernel.org>]

On Wed 08-08-18 10:16:01, Vlastimil Babka wrote:
> On 08/07/2018 09:54 PM, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@suse.com>
> > 
> > eacd86ca3b03 ("net/netfilter/x_tables.c: use kvmalloc()
> > in xt_alloc_table_info()") has unintentionally fortified
> > xt_alloc_table_info allocation when __GFP_RETRY has been dropped from
> > the vmalloc fallback. Later on there was a syzbot report that this
> > can lead to OOM killer invocations when tables are too large and
> > 0537250fdc6c ("netfilter: x_tables: make allocation less aggressive")
> > has been merged to restore the original behavior. Georgi Nikolov however
> > noticed that he is not able to install his iptables anymore so this can
> > be seen as a regression.
> > 
> > The primary argument for 0537250fdc6c was that this allocation path
> > shouldn't really trigger the OOM killer and kill innocent tasks. On the
> > other hand the interface requires root and as such should allow what the
> > admin asks for. Root inside a namespaces makes this more complicated
> > because those might be not trusted in general. If they are not then such
> > namespaces should be restricted anyway. Therefore drop the __GFP_NORETRY
> > and replace it by __GFP_ACCOUNT to enfore memcg constrains on it.
> > 
> > Fixes: 0537250fdc6c ("netfilter: x_tables: make allocation less aggressive")
> > Reported-by: Georgi Nikolov <gnikolov@icdsoft.com>
> > Suggested-by: Vlastimil Babka <vbabka@suse.cz>
> > Acked-by: Florian Westphal <fw@strlen.de>
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks!

> IIRC According to Florian there are more places like this in the
> netfilter code?

Well, this is more for netfilter guys. I can only give a general
guidance that generally untrusted allocations triggered from userspace
should be a subject of kmem accounting.

-- 
Michal Hocko
SUSE Labs