Michal Hocko <mhocko@xxxxxxxx> writes:
> On Wed 14-12-22 17:21:10, 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+
>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Thanks for catching this!
>
> Btw. looking at the code again it seems rather pointless to duplicate
> the policy just to throw it away anyway. A slightly bigger diff but this
> looks more reasonable to me. What do you think? I can also send it as a
> clean up on top of your fix.
> ---
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 61aa9aedb728..918cdc8a7f0c 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1489,7 +1489,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
> {
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma;
> - struct mempolicy *new;
> + struct mempolicy *new. *old;
> unsigned long vmstart;
> unsigned long vmend;
> unsigned long end;
> @@ -1521,30 +1521,28 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
> return 0;
> mmap_write_lock(mm);
> for_each_vma_range(vmi, vma, end) {
> - vmstart = max(start, vma->vm_start);
> - vmend = min(end, vma->vm_end);
> - new = mpol_dup(vma_policy(vma));
> - if (IS_ERR(new)) {
> - err = PTR_ERR(new);
> - break;
> - }
> - /*
> - * Only update home node if there is an existing vma policy
> - */
> - if (!new)
> - continue;
> -
> /*
> * If any vma in the range got policy other than MPOL_BIND
> * or MPOL_PREFERRED_MANY we return error. We don't reset
> * the home node for vmas we already updated before.
> */
> - if (new->mode != MPOL_BIND && new->mode != MPOL_PREFERRED_MANY) {
> + old = vma_policy(vma);
> + if (!old)
> + continue;
> + if (old->mode != MPOL_BIND && old->mode != MPOL_PREFERRED_MANY) {
> err = -EOPNOTSUPP;
> break;
> }
>
> + new = mpol_dup(vma_policy(vma));
new = mpol_dup(old);
> + if (IS_ERR(new)) {
> + err = PTR_ERR(new);
> + break;
> + }
> +
> new->home_node = home_node;
> + vmstart = max(start, vma->vm_start);
> + vmend = min(end, vma->vm_end);
> err = mbind_range(mm, vmstart, vmend, new);
> mpol_put(new);
> if (err)
> --
> Michal Hocko
> SUSE Labs
