Commit 803bf5ec authored Feb 10, 2010 by Michael Neuling Committed by Linus Torvalds Feb 11, 2010

fs/exec.c: restrict initial stack space expansion to rlimit



When reserving stack space for a new process, make sure we're not
attempting to expand the stack by more than rlimit allows.

This fixes a bug caused by b6a2fea3 ("mm:
variable length argument support") and unmasked by
fc63cf23 ("exec: setup_arg_pages() fails
to return errors").

This bug means that when limiting the stack to less the 20*PAGE_SIZE (eg.
80K on 4K pages or 'ulimit -s 79') all processes will be killed before
they start.  This is particularly bad with 64K pages, where a ulimit below
1280K will kill every process.

To test, do:

  'ulimit -s 15; ls'

before and after the patch is applied.  Before it's applied, 'ls' should
be killed.  After the patch is applied, 'ls' should no longer be killed.

A stack limit of 15KB since it's small enough to trigger 20*PAGE_SIZE.
Also 15KB not a multiple of PAGE_SIZE, which is a trickier case to handle
correctly with this code.

4K pages should be fine to test with.

[kosaki.motohiro@jp.fujitsu.com: cleanup]
[akpm@linux-foundation.org: cleanup cleanup]
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Americo Wang <xiyou.wangcong@gmail.com>
Cc: Anton Blanchard <anton@samba.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: James Morris <jmorris@namei.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 4cfbafd3

fs/exec.c

+19 −2

Original line number	Diff line number	Diff line
		@@ -571,6 +571,9 @@ int setup_arg_pages(struct linux_binprm *bprm,
		struct vm_area_struct *prev = NULL;
		unsigned long vm_flags;
		unsigned long stack_base;
		unsigned long stack_size;
		unsigned long stack_expand;
		unsigned long rlim_stack;

		#ifdef CONFIG_STACK_GROWSUP
		/* Limit stack size to 1GB */
		@@ -627,10 +630,24 @@ int setup_arg_pages(struct linux_binprm *bprm,
		goto out_unlock;
		}

		stack_expand = EXTRA_STACK_VM_PAGES * PAGE_SIZE;
		stack_size = vma->vm_end - vma->vm_start;
		/*
		* Align this down to a page boundary as expand_stack
		* will align it up.
		*/
		rlim_stack = rlimit(RLIMIT_STACK) & PAGE_MASK;
		rlim_stack = min(rlim_stack, stack_size);
		#ifdef CONFIG_STACK_GROWSUP
		stack_base = vma->vm_end + EXTRA_STACK_VM_PAGES * PAGE_SIZE;
		if (stack_size + stack_expand > rlim_stack)
		stack_base = vma->vm_start + rlim_stack;
		else
		stack_base = vma->vm_end + stack_expand;
		#else
		stack_base = vma->vm_start - EXTRA_STACK_VM_PAGES * PAGE_SIZE;
		if (stack_size + stack_expand > rlim_stack)
		stack_base = vma->vm_end - rlim_stack;
		else
		stack_base = vma->vm_start - stack_expand;
		#endif
		ret = expand_stack(vma, stack_base);
		if (ret)

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