Commit b2c56e4f authored Sep 11, 2013 by Oleg Nesterov Committed by Linus Torvalds Sep 11, 2013

mm: shift VM_GROWS* check from mmap_region() to do_mmap_pgoff()



mmap() doesn't allow the non-anonymous mappings with VM_GROWS* bit set.
In particular this means that mmap_region()->vma_merge(file, vm_flags)
must always fail if "vm_flags & VM_GROWS" is set incorrectly.

So it does not make sense to check VM_GROWS* after we already allocated
the new vma, the only caller, do_mmap_pgoff(), which can pass this flag
can do the check itself.

And this looks a bit more correct, mmap_region() already unmapped the
old mapping at this stage. But if mmap() is going to fail, it should
avoid do_munmap() if possible.

Note: we check VM_GROWS at the end to ensure that do_mmap_pgoff() won't
return EINVAL in the case when it currently returns another error code.

Many thanks to Hugh who nacked the buggy v1.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 465c47fd

mm/mmap.c

+4 −6

Original line number	Diff line number	Diff line
		@@ -1302,6 +1302,8 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,

		if (!file->f_op \|\| !file->f_op->mmap)
		return -ENODEV;
		if (vm_flags & (VM_GROWSDOWN\|VM_GROWSUP))
		return -EINVAL;
		break;

		default:
		@@ -1310,6 +1312,8 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
		} else {
		switch (flags & MAP_TYPE) {
		case MAP_SHARED:
		if (vm_flags & (VM_GROWSDOWN\|VM_GROWSUP))
		return -EINVAL;
		/*
		* Ignore pgoff.
		*/
		@@ -1544,11 +1548,7 @@ munmap_back:
		vma->vm_pgoff = pgoff;
		INIT_LIST_HEAD(&vma->anon_vma_chain);

		error = -EINVAL; /* when rejecting VM_GROWSDOWN\|VM_GROWSUP */

		if (file) {
		if (vm_flags & (VM_GROWSDOWN\|VM_GROWSUP))
		goto free_vma;
		if (vm_flags & VM_DENYWRITE) {
		error = deny_write_access(file);
		if (error)
		@@ -1573,8 +1573,6 @@ munmap_back:
		pgoff = vma->vm_pgoff;
		vm_flags = vma->vm_flags;
		} else if (vm_flags & VM_SHARED) {
		if (unlikely(vm_flags & (VM_GROWSDOWN\|VM_GROWSUP)))
		goto free_vma;
		error = shmem_zero_setup(vma);
		if (error)
		goto free_vma;

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