netfilter: x_tables: make allocation less aggressive

syzbot has noticed that xt_alloc_table_info can allocate a lot of memory.
This is an admin only interface but an admin in a namespace is sufficient
as well.  eacd86ca3b03 ("net/netfilter/x_tables.c: use kvmalloc() in
xt_alloc_table_info()") has changed the opencoded kmalloc->vmalloc
fallback into kvmalloc.  It has dropped __GFP_NORETRY on the way because
vmalloc has simply never fully supported __GFP_NORETRY semantic.  This is
still the case because e.g.  page tables backing the vmalloc area are
hardcoded GFP_KERNEL.

Revert back to __GFP_NORETRY as a poors man defence against excessively
large allocation request here.  We will not rule out the OOM killer
completely but __GFP_NORETRY should at least stop the large request in
most cases.

[akpm@linux-foundation.org: coding-style fixes]
tableLink: http://lkml.kernel.org/r/20180130140104.GE21609@dhcp22.suse.cz
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 8fa4d37..2f685ee 100644 (file)
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -1008,7 +1008,12 @@ struct xt_table_info *xt_alloc_table_info(unsigned int size)
        if ((size >> PAGE_SHIFT) + 2 > totalram_pages)
                return NULL;
 
-       info = kvmalloc(sz, GFP_KERNEL);
+       /* __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);
        if (!info)
                return NULL;