linux-kernel - [PATCH v2 11/11] protect architectures where THREAD_SIZE >= PAGE

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Date:	Thu,  9 Aug 2012 17:01:19 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	<linux-kernel@...r.kernel.org>
Cc:	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
	<devel@...nvz.org>, Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<kamezawa.hiroyu@...fujitsu.com>, Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Glauber Costa <glommer@...allels.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: [PATCH v2 11/11] protect architectures where THREAD_SIZE >= PAGE_SIZE against fork bombs

Because those architectures will draw their stacks directly from the
page allocator, rather than the slab cache, we can directly pass
__GFP_KMEMCG flag, and issue the corresponding free_pages.

This code path is taken when the architecture doesn't define
CONFIG_ARCH_THREAD_INFO_ALLOCATOR (only ia64 seems to), and has
THREAD_SIZE >= PAGE_SIZE. Luckily, most - if not all - of the remaining
architectures fall in this category.

This will guarantee that every stack page is accounted to the memcg the
process currently lives on, and will have the allocations to fail if
they go over limit.

For the time being, I am defining a new variant of THREADINFO_GFP, not
to mess with the other path. Once the slab is also tracked by memcg, we
can get rid of that flag.

Tested to successfully protect against :(){ :|:& };:

Signed-off-by: Glauber Costa <glommer@...allels.com>
Acked-by: Frederic Weisbecker <fweisbec@...hat.com>
CC: Christoph Lameter <cl@...ux.com>
CC: Pekka Enberg <penberg@...helsinki.fi>
CC: Michal Hocko <mhocko@...e.cz>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC: Johannes Weiner <hannes@...xchg.org>
CC: Suleiman Souhlal <suleiman@...gle.com>
---
 include/linux/thread_info.h | 2 ++
 kernel/fork.c               | 4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index ccc1899..e7e0473 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -61,6 +61,8 @@ extern long do_no_restart_syscall(struct restart_block *parm);
 # define THREADINFO_GFP		(GFP_KERNEL | __GFP_NOTRACK)
 #endif
 
+#define THREADINFO_GFP_ACCOUNTED (THREADINFO_GFP | __GFP_KMEMCG)
+
 /*
  * flag set/clear/test wrappers
  * - pass TIF_xxxx constants to these functions
diff --git a/kernel/fork.c b/kernel/fork.c
index dc3ff16..b0b90c3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -142,7 +142,7 @@ void __weak arch_release_thread_info(struct thread_info *ti) { }
 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 						  int node)
 {
-	struct page *page = alloc_pages_node(node, THREADINFO_GFP,
+	struct page *page = alloc_pages_node(node, THREADINFO_GFP_ACCOUNTED,
 					     THREAD_SIZE_ORDER);
 
 	return page ? page_address(page) : NULL;
@@ -151,7 +151,7 @@ static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 static inline void free_thread_info(struct thread_info *ti)
 {
 	arch_release_thread_info(ti);
-	free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
+	free_accounted_pages((unsigned long)ti, THREAD_SIZE_ORDER);
 }
 # else
 static struct kmem_cache *thread_info_cache;
-- 
1.7.11.2

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