On 08/02/2018 10:50 AM, Michal Hocko wrote: > On Wed 01-08-18 19:03:03, Georgi Nikolov wrote: >> >> *Georgi Nikolov* >> System Administrator >> www.icdsoft.com <http://www.icdsoft.com> >> >> On 08/01/2018 11:33 AM, Michal Hocko wrote: >>> On Wed 01-08-18 09:34:23, Vlastimil Babka wrote: >>>> On 07/31/2018 04:05 PM, Florian Westphal wrote: >>>>> Georgi Nikolov <gnikolov@xxxxxxxxxxx> wrote: >>>>>>> No, I think that's rather for the netfilter folks to decide. However, it >>>>>>> seems there has been the debate already [1] and it was not found. The >>>>>>> conclusion was that __GFP_NORETRY worked fine before, so it should work >>>>>>> again after it's added back. But now we know that it doesn't... >>>>>>> >>>>>>> [1] https://lore.kernel.org/lkml/20180130140104.GE21609@xxxxxxxxxxxxxx/T/#u >>>>>> Yes i see. I will add Florian Westphal to CC list. netfilter-devel is >>>>>> already in this list so probably have to wait for their opinion. >>>>> It hasn't changed, I think having OOM killer zap random processes >>>>> just because userspace wants to import large iptables ruleset is not a >>>>> good idea. >>>> If we denied the allocation instead of OOM (e.g. by using >>>> __GFP_RETRY_MAYFAIL), a slightly smaller one may succeed, still leaving >>>> the system without much memory, so it will invoke OOM killer sooner or >>>> later anyway. >>>> >>>> I don't see any silver-bullet solution, unfortunately. If this can be >>>> abused by (multiple) namespaces, then they have to be contained by >>>> kmemcg as that's the generic mechanism intended for this. Then we could >>>> use the __GFP_RETRY_MAYFAIL. >>>> The only limit we could impose to outright deny the allocation (to >>>> prevent obvious bugs/admin mistakes or abuses) could be based on the >>>> amount of RAM, as was suggested in the old thread. >> >> Can we make this configurable - on/off switch or size above which >> to pass GFP_NORETRY. > > Yet another tunable? How do you decide which one to select? Seriously, > configuration knobs sound attractive but they are rarely a good idea. > Either we trust privileged users or we don't and we have kmem accounting > for that. > >> Probably hard coded based on amount of RAM is a good idea too. > > How do you scale that? > > In other words, why don't we simply do the following? Note that this is > not tested. I have also no idea what is the lifetime of this allocation. > Is it bound to any specific process or is it a namespace bound? If the > later then the memcg OOM killer might wipe the whole memcg down without > making any progress. This would make the whole namespace unsuable until > somebody intervenes. Is this acceptable? > --- > From 4dec96eb64954a7e58264ed551afadf62ca4c5f7 Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@xxxxxxxx> > Date: Thu, 2 Aug 2018 10:38:57 +0200 > Subject: [PATCH] netfilter/x_tables: do not fail xt_alloc_table_info too > easilly > > 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@xxxxxxxxxxx> > Suggested-by: Vlastimil Babka <vbabka@xxxxxxx> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> > --- > net/netfilter/x_tables.c | 7 +------ > 1 file changed, 1 insertion(+), 6 deletions(-) > > diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c > index d0d8397c9588..b769408e04ab 100644 > --- a/net/netfilter/x_tables.c > +++ b/net/netfilter/x_tables.c > @@ -1178,12 +1178,7 @@ struct xt_table_info *xt_alloc_table_info(unsigned int size) > if (sz < sizeof(*info) || sz >= XT_MAX_TABLE_SIZE) > return NULL; > > - /* __GFP_NORETRY is not fully supported by kvmalloc but it should > - * work reasonably well if sz is too large and bail out rather > - * than shoot all processes down before realizing there is nothing > - * more to reclaim. > - */ > - info = kvmalloc(sz, GFP_KERNEL | __GFP_NORETRY); > + info = kvmalloc(sz, GFP_KERNEL | __GFP_ACCOUNT); GFP_KERNEL_ACCOUNT ? > if (!info) > return NULL; > >
