ACK: [CVE-2017-7616][PATCH Trusty] mm/mempolicy.c: fix error handling in set_mempolicy and mbind.

[Stefan Bader]

On 25.07.2017 13:42, Po-Hsu Lin wrote:
> From: Chris Salls <salls at cs.ucsb.edu>
> 
> CVE-2017-7616
> 
> In the case that compat_get_bitmap fails we do not want to copy the
> bitmap to the user as it will contain uninitialized stack data and leak
> sensitive data.
> 
> Signed-off-by: Chris Salls <salls at cs.ucsb.edu>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> (cherry picked from commit cf01fb9985e8deb25ccf0ea54d916b8871ae0e62)
> Signed-off-by: Po-Hsu Lin <po-hsu.lin at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>

> ---
>  mm/mempolicy.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 5990620..c5802e4 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1590,7 +1590,6 @@ asmlinkage long compat_sys_get_mempolicy(int __user *policy,
>  asmlinkage long compat_sys_set_mempolicy(int mode, compat_ulong_t __user *nmask,
>  				     compat_ulong_t maxnode)
>  {
> -	long err = 0;
>  	unsigned long __user *nm = NULL;
>  	unsigned long nr_bits, alloc_size;
>  	DECLARE_BITMAP(bm, MAX_NUMNODES);
> @@ -1599,14 +1598,13 @@ asmlinkage long compat_sys_set_mempolicy(int mode, compat_ulong_t __user *nmask,
>  	alloc_size = ALIGN(nr_bits, BITS_PER_LONG) / 8;
>  
>  	if (nmask) {
> -		err = compat_get_bitmap(bm, nmask, nr_bits);
> +		if (compat_get_bitmap(bm, nmask, nr_bits))
> +			return -EFAULT;
>  		nm = compat_alloc_user_space(alloc_size);
> -		err |= copy_to_user(nm, bm, alloc_size);
> +		if (copy_to_user(nm, bm, alloc_size))
> +			return -EFAULT;
>  	}
>  
> -	if (err)
> -		return -EFAULT;
> -
>  	return sys_set_mempolicy(mode, nm, nr_bits+1);
>  }
>  
> @@ -1614,7 +1612,6 @@ asmlinkage long compat_sys_mbind(compat_ulong_t start, compat_ulong_t len,
>  			     compat_ulong_t mode, compat_ulong_t __user *nmask,
>  			     compat_ulong_t maxnode, compat_ulong_t flags)
>  {
> -	long err = 0;
>  	unsigned long __user *nm = NULL;
>  	unsigned long nr_bits, alloc_size;
>  	nodemask_t bm;
> @@ -1623,14 +1620,13 @@ asmlinkage long compat_sys_mbind(compat_ulong_t start, compat_ulong_t len,
>  	alloc_size = ALIGN(nr_bits, BITS_PER_LONG) / 8;
>  
>  	if (nmask) {
> -		err = compat_get_bitmap(nodes_addr(bm), nmask, nr_bits);
> +		if (compat_get_bitmap(nodes_addr(bm), nmask, nr_bits))
> +			return -EFAULT;
>  		nm = compat_alloc_user_space(alloc_size);
> -		err |= copy_to_user(nm, nodes_addr(bm), alloc_size);
> +		if (copy_to_user(nm, nodes_addr(bm), alloc_size))
> +			return -EFAULT;
>  	}
>  
> -	if (err)
> -		return -EFAULT;
> -
>  	return sys_mbind(start, len, mode, nm, nr_bits+1, flags);
>  }
>  
> 


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