Re: [RFC PATCH] mm/mempolicy: Fix memory leak in set_mempolicy_home_node system call

[Randy Dunlap]

On 12/14/22 14:21, Mathieu Desnoyers wrote:
> When encountering any vma in the range with policy other than MPOL_BIND
> or MPOL_PREFERRED_MANY, an error is returned without issuing a mpol_put
> on the policy just allocated with mpol_dup().
> 
> This allows arbitrary users to leak kernel memory.
> 
> Fixes: c6018b4b2549 ("mm/mempolicy: add set_mempolicy_home_node syscall")
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
> Cc: Ben Widawsky <ben.widawsky@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Feng Tang <feng.tang@xxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Huang Ying <ying.huang@xxxxxxxxx>
> Cc: <linux-api@xxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # 5.17+

Reviewed-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>

Thanks.

> ---
>  mm/mempolicy.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 61aa9aedb728..02c8a712282f 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1540,6 +1540,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
>  		 * the home node for vmas we already updated before.
>  		 */
>  		if (new->mode != MPOL_BIND && new->mode != MPOL_PREFERRED_MANY) {
> +			mpol_put(new);
>  			err = -EOPNOTSUPP;
>  			break;
>  		}

-- 
~Randy