Commit 2ad306b1 authored Dec 18, 2012 by Glauber Costa Committed by Linus Torvalds Dec 18, 2012

fork: 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@parallels.com>
Acked-by: Frederic Weisbecker <fweisbec@redhat.com>
Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: JoonSoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Rik van Riel <riel@redhat.com>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent c8b2a36f

include/linux/thread_info.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -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

kernel/fork.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -146,7 +146,7 @@ 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;
		@@ -154,7 +154,7 @@ static struct thread_info alloc_thread_info_node(struct task_struct tsk,

		static inline void free_thread_info(struct thread_info *ti)
		{
		free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
		free_memcg_kmem_pages((unsigned long)ti, THREAD_SIZE_ORDER);
		}
		# else
		static struct kmem_cache *thread_info_cache;

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