mm/mmap.c: expand_downwards: don't require the gap if !vm_prev (32e4e6d5) · Commits · 戴 / test

expand_stack(vma) fails if address < stack_guard_gap even if there is no vma->vm_prev. I don't think this makes sense, and we didn't do this before the recent commit ("mm: larger stack guard gap, between vmas"). We do not need a gap in this case, any address is fine as long as security_mmap_addr() doesn't object. This also simplifies the code, we know that address >= prev->vm_end and thus underflow is not possible. Link: http://lkml.kernel.org/r/20170628175258.GA24881@redhat.com Signed-off-by:

Oleg Nesterov <oleg@redhat.com> Acked-by:

Michal Hocko <mhocko@suse.com> Cc: Hugh Dickins <hughd@google.com> Cc: Larry Woodman <lwoodman@redhat.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

+3 −7

Original line number	Original line	Diff line number	Diff line
	@@ -2316,7 +2316,6 @@ int expand_downwards(struct vm_area_struct *vma,
	{		{
	struct mm_struct *mm = vma->vm_mm;		struct mm_struct *mm = vma->vm_mm;
	struct vm_area_struct *prev;		struct vm_area_struct *prev;
	unsigned long gap_addr;
	int error;		int error;

	address &= PAGE_MASK;		address &= PAGE_MASK;
	@@ -2325,15 +2324,12 @@ int expand_downwards(struct vm_area_struct *vma,
	return error;		return error;

	/* Enforce stack_guard_gap */		/* Enforce stack_guard_gap */
	gap_addr = address - stack_guard_gap;
	if (gap_addr > address)
	return -ENOMEM;
	prev = vma->vm_prev;		prev = vma->vm_prev;
	if (prev && prev->vm_end > gap_addr &&		/* Check that both stack segments have the same anon_vma? */
			if (prev && !(prev->vm_flags & VM_GROWSDOWN) &&
	(prev->vm_flags & (VM_WRITE\|VM_READ\|VM_EXEC))) {		(prev->vm_flags & (VM_WRITE\|VM_READ\|VM_EXEC))) {
	if (!(prev->vm_flags & VM_GROWSDOWN))		if (address - prev->vm_end < stack_guard_gap)
	return -ENOMEM;		return -ENOMEM;
	/* Check that both stack segments have the same anon_vma? */
	}		}

	/* We must make sure the anon_vma is allocated. */		/* We must make sure the anon_vma is allocated. */

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