Re: [v3 PATCH 3/3] mm/mempolicy: unify the parameter sanity check for mbind and set_mempolicy

[Michal Hocko]

On Mon 31-05-21 22:05:56, Feng Tang wrote:
> Currently the kernel_mbind() and kernel_set_mempolicy() do almost
> the same operation for parameter sanity check.
> 
> Add a helper function to unify the code to reduce the redundancy,
> and make it easier for changing the pre-processing code in future.
> 
> [thanks to David Rientjes for suggesting using helper function
> instead of macro]
> 
> Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>

sanitize_mpol_flags would benefit from some high level comments
explaining those modifications but this can be done on top. This looks
like a useful cleanup on its own

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

Thanks!

> ---
>  mm/mempolicy.c | 47 +++++++++++++++++++++++++++++------------------
>  1 file changed, 29 insertions(+), 18 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index c337bd7..85ef512 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1444,26 +1444,37 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode,
>  	return copy_to_user(mask, nodes_addr(*nodes), copy) ? -EFAULT : 0;
>  }
>  
> +static inline int sanitize_mpol_flags(int *mode, unsigned short *flags)
> +{
> +	*flags = *mode & MPOL_MODE_FLAGS;
> +	*mode &= ~MPOL_MODE_FLAGS;
> +	if ((unsigned int)(*mode) >= MPOL_MAX)
> +		return -EINVAL;
> +	if ((*flags & MPOL_F_STATIC_NODES) && (*flags & MPOL_F_RELATIVE_NODES))
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
>  static long kernel_mbind(unsigned long start, unsigned long len,
>  			 unsigned long mode, const unsigned long __user *nmask,
>  			 unsigned long maxnode, unsigned int flags)
>  {
> +	unsigned short mode_flags;
>  	nodemask_t nodes;
> +	int lmode = mode;
>  	int err;
> -	unsigned short mode_flags;
>  
>  	start = untagged_addr(start);
> -	mode_flags = mode & MPOL_MODE_FLAGS;
> -	mode &= ~MPOL_MODE_FLAGS;
> -	if (mode >= MPOL_MAX)
> -		return -EINVAL;
> -	if ((mode_flags & MPOL_F_STATIC_NODES) &&
> -	    (mode_flags & MPOL_F_RELATIVE_NODES))
> -		return -EINVAL;
> +	err = sanitize_mpol_flags(&lmode, &mode_flags);
> +	if (err)
> +		return err;
> +
>  	err = get_nodes(&nodes, nmask, maxnode);
>  	if (err)
>  		return err;
> -	return do_mbind(start, len, mode, mode_flags, &nodes, flags);
> +
> +	return do_mbind(start, len, lmode, mode_flags, &nodes, flags);
>  }
>  
>  SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
> @@ -1477,20 +1488,20 @@ SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
>  static long kernel_set_mempolicy(int mode, const unsigned long __user *nmask,
>  				 unsigned long maxnode)
>  {
> -	int err;
> +	unsigned short mode_flags;
>  	nodemask_t nodes;
> -	unsigned short flags;
> +	int lmode = mode;
> +	int err;
> +
> +	err = sanitize_mpol_flags(&lmode, &mode_flags);
> +	if (err)
> +		return err;
>  
> -	flags = mode & MPOL_MODE_FLAGS;
> -	mode &= ~MPOL_MODE_FLAGS;
> -	if ((unsigned int)mode >= MPOL_MAX)
> -		return -EINVAL;
> -	if ((flags & MPOL_F_STATIC_NODES) && (flags & MPOL_F_RELATIVE_NODES))
> -		return -EINVAL;
>  	err = get_nodes(&nodes, nmask, maxnode);
>  	if (err)
>  		return err;
> -	return do_set_mempolicy(mode, flags, &nodes);
> +
> +	return do_set_mempolicy(lmode, mode_flags, &nodes);
>  }
>  
>  SYSCALL_DEFINE3(set_mempolicy, int, mode, const unsigned long __user *, nmask,
> -- 
> 2.7.4

-- 
Michal Hocko
SUSE Labs