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

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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 b6a2fea393 ("mm:
variable length argument support") and unmasked by
fc63cf2370 ("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.

[[email protected]: cleanup]
[[email protected]: cleanup cleanup]
Signed-off-by: Michael Neuling <[email protected]>
Signed-off-by: KOSAKI Motohiro <[email protected]>
Cc: Americo Wang <[email protected]>
Cc: Anton Blanchard <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: James Morris <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Serge Hallyn <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Michael Neuling 2010-02-10 13:56:42 -08:00 • committed by Linus Torvalds
commit 803bf5ec25
1 changed files with 19 additions and 2 deletions
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21
fs/exec.c
View file

@ -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)