On 2022/8/19 13:23, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Thu, Aug 18, 2022 at 09:00:14PM +0800, Miaohe Lin wrote:
>> After kill_procs(), tk will be freed without being removed from the to_kill
>> list. In the next iteration, the freed list entry in the to_kill list will
>> be accessed, thus leading to use-after-free issue.
>
> kill_procs() runs over the to_kill list and frees all listed items in each
> iteration. So just after returning from unmap_and_kill(), to_kill->next and
> to_kill->prev still point to the addresses of struct to_kill which was the
> first or last item (already freed!). This is bad-manered, but
> collect_procs_fsdax() in the next iteration calls list_add_tail() and
> overwrites the dangling pointers with newly allocated item. So this problem
list_add_tail will do WRITE_ONCE(prev->next, new) where prev is already freed!
Or am I miss something?
> should not be so critical? Anyway, I agree with fixing this fragile code.
>
>> Fix it by reinitializing
>> the to_kill list after unmap_and_kill().
>>
>> Fixes: c36e20249571 ("mm: introduce mf_dax_kill_procs() for fsdax case")
>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>
>> ---
>> mm/memory-failure.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index 7023c3d81273..a2f4e8b00a26 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -1658,6 +1658,8 @@ int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
>> collect_procs_fsdax(page, mapping, index, &to_kill);
>> unmap_and_kill(&to_kill, page_to_pfn(page), mapping,
>> index, mf_flags);
>> + /* Reinitialize to_kill list for later resuing. */
>
> s/resuing/reusing/ ?
OK.
>
>> + INIT_LIST_HEAD(&to_kill);
>
> How about adding list_del() in kill_procs()? Other callers now use
> to_kill only once, but fixing generally looks tidier to me.
That's a good idea. Will do it in v2. Many thanks for your review, Naoya!
Thanks,
Miaohe Lin
>
> Thanks,
> Naoya Horiguchi
>
