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.

[[email protected]: coding-style fixes]
Fixes: eacd86ca3b03 ("net/netfilter/x_tables.c: use kvmalloc() in xt_alloc_tableLink: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Michal Hocko <[email protected]>
Acked-by: Florian Westphal <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Cc: David S. Miller <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>

1 files changed, 6 insertions, 1 deletions

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 8fa4d37141a7..2f685ee1f9c8 100644
--- 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;