linux-kernel - Re: net/sctp: vmalloc allocation failure in sctp_setsockopt/xt_alloc_table

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Date:   Mon, 28 Nov 2016 13:13:12 -0200
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Neil Horman <nhorman@...driver.com>
Cc:     Andrey Konovalov <andreyknvl@...gle.com>,
        Vlad Yasevich <vyasevich@...il.com>,
        linux-sctp@...r.kernel.org, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Patrick McHardy <kaber@...sh.net>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        "David S. Miller" <davem@...emloft.net>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/sctp: vmalloc allocation failure in
 sctp_setsockopt/xt_alloc_table_info

On Mon, Nov 28, 2016 at 09:39:31AM -0500, Neil Horman wrote:
> On Mon, Nov 28, 2016 at 03:33:40PM +0100, Andrey Konovalov wrote:
> > On Mon, Nov 28, 2016 at 3:13 PM, Neil Horman <nhorman@...driver.com> wrote:
> > > On Mon, Nov 28, 2016 at 02:00:19PM +0100, Andrey Konovalov wrote:
> > >> Hi!
> > >>
> > >> I've got the following error report while running the syzkaller fuzzer.
> > >>
> > >> On commit d8e435f3ab6fea2ea324dce72b51dd7761747523 (Nov 26).
> > >>
> > >> A reproducer is attached.
> > >>
> > >> a.out: vmalloc: allocation failure, allocated 823562240 of 1427091456
> > >> bytes, mode:0x24000c2(GFP_KERNEL|__GFP_HIGHMEM)
> > >>
> > > How much total ram do you have in this system?  The call appears to be
> > > attempting to allocate 1.3 Gb of data.  Even using vmalloc to allow
> > > discontiguous allocation, thats alot of memory, and if enough is in use already,
> > > I could make the argument that this might be expected behavior.
> > 
> > Hi Neail,
> > 
> > I have 2 Gb.
> > 
> That would be why.  Allocating 65% of the available system memory will almost
> certainly lead to OOM failures quickly.
> 
> > Just tested with 4 Gb, everything seems to be working fine.
> > So I guess this is not actually a bug and allocating 1.3 Gb is OK.

Still we probably should avoid the warn triggered by an userspace
application: (untested)

--8<--

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index fc4977456c30..b56a0e128fc3 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -958,7 +958,8 @@ struct xt_table_info *xt_alloc_table_info(unsigned int size)
 	if (sz <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER))
 		info = kmalloc(sz, GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY);
 	if (!info) {
-		info = vmalloc(sz);
+		info = __vmalloc(sz, GFP_KERNEL | __GFP_NOWARN | __GFP_HIGHMEM,
+				 PAGE_KERNEL);
 		if (!info)
 			return NULL;
 	}