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

[James Morris]

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@xxxxxxxxxx>

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@xxxxxxxxx>
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