linux-kernel - [PATCH 4.15 32/72] netfilter: x_tables: make allocation less aggressive

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Date:   Fri,  6 Apr 2018 15:24:07 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Michal Hocko <mhocko@...e.com>,
        Florian Westphal <fw@...len.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Pablo Neira Ayuso <pablo@...filter.org>
Subject: [PATCH 4.15 32/72] netfilter: x_tables: make allocation less aggressive

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michal Hocko <mhocko@...nel.org>

commit 0537250fdc6c876ed4cbbe874c739aebef493ee2 upstream.

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@...ux-foundation.org: coding-style fixes]
Fixes: eacd86ca3b03 ("net/netfilter/x_tables.c: use kvmalloc() in xt_alloc_tableLink: http://lkml.kernel.org/r/20180130140104.GE21609@dhcp22.suse.cz
Signed-off-by: Michal Hocko <mhocko@...e.com>
Acked-by: Florian Westphal <fw@...len.de>
Reviewed-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: David S. Miller <davem@...emloft.net>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/netfilter/x_tables.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -1008,7 +1008,12 @@ struct xt_table_info *xt_alloc_table_inf
 	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;