Commit 690eac53 authored Jan 11, 2015 by Linus Torvalds

mm: Don't count the stack guard page towards RLIMIT_STACK



Commit fee7e49d ("mm: propagate error from stack expansion even for
guard page") made sure that we return the error properly for stack
growth conditions.  It also theorized that counting the guard page
towards the stack limit might break something, but also said "Let's see
if anybody notices".

Somebody did notice.  Apparently android-x86 sets the stack limit very
close to the limit indeed, and including the guard page in the rlimit
check causes the android 'zygote' process problems.

So this adds the (fairly trivial) code to make the stack rlimit check be
against the actual real stack size, rather than the size of the vma that
includes the guard page.

Reported-and-tested-by: Chih-Wei Huang <cwhuang@android-x86.org>
Cc: Jay Foad <jay.foad@gmail.com>
Cc: stable@kernel.org  # to match back-porting of fee7e49d
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 4850d37d

mm/mmap.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -2099,14 +2099,17 @@ static int acct_stack_growth(struct vm_area_struct *vma, unsigned long size, uns
		{
		struct mm_struct *mm = vma->vm_mm;
		struct rlimit *rlim = current->signal->rlim;
		unsigned long new_start;
		unsigned long new_start, actual_size;

		/* address space limit tests */
		if (!may_expand_vm(mm, grow))
		return -ENOMEM;

		/* Stack limit test */
		if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur))
		actual_size = size;
		if (size && (vma->vm_flags & (VM_GROWSUP \| VM_GROWSDOWN)))
		actual_size -= PAGE_SIZE;
		if (actual_size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur))
		return -ENOMEM;

		/* mlock limit tests */

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