Re: [PATCH 1/3] mmap: protect from stack expantion into low vm addresses

James Morris
2007-11-27T01:05:18Z

On Mon, 26 Nov 2007, Eric Paris wrote:

> Add security checks to make sure we are not attempting to expand the
> stack into memory protected by mmap_min_addr
>
> Signed-off-by: Eric Paris <eparis@redhat.com>

Please include the LSMs list in the CC line (added again) for posts
relating to security.

Applied to
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/selinux-2.6.git#for-akpm

> ---
>
> ** Be very careful applying/rediffing this patch. Standard 3 lines of
> context from git diff will misapply the first hunk to expand_upwards
> instead of properly in expand_downwards. This patch was generated using
> -U 4 to make sure it applies in the correct place. **

Seems to have applied correctly for me.

>
> mm/mmap.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> --- kernel-1/mm/mmap.c
> +++ kernel-2/mm/mmap.c
> @@ -1614,17 +1614,21 @@ static inline int expand_downwards(struc
> * so that the anon_vma locking is not a noop.
> */
> if (unlikely(anon_vma_prepare(vma)))
> return -ENOMEM;
> +
> + address &= PAGE_MASK;
> + error = security_file_mmap(0, 0, 0, 0, address, 1);
> + if (error)
> + return error;
> +
> anon_vma_lock(vma);
>
> /*
> * vma->vm_start/vm_end cannot change under us because the caller
> * is required to hold the mmap_sem in read mode. We need the
> * anon_vma lock to serialize against concurrent expand_stacks.
> */
> - address &= PAGE_MASK;
> - error = 0;
>
> /* Somebody else might have raced and expanded it already */
> if (address < vma->vm_start) {
> unsigned long size, grow;
>
>

--
James Morris
<jmorris@namei.org>