* [bug report] mm: huge_memory: enable debugfs to split huge pages to any order
@ 2024-03-07 13:49 Dan Carpenter
2024-03-07 14:20 ` Zi Yan
0 siblings, 1 reply; 5+ messages in thread
From: Dan Carpenter @ 2024-03-07 13:49 UTC (permalink / raw)
To: ziy; +Cc: linux-mm
Hello Zi Yan,
Commit fc4d182316bd ("mm: huge_memory: enable debugfs to split huge
pages to any order") from Feb 26, 2024 (linux-next), leads to the
following Smatch static checker warning:
mm/huge_memory.c:2898 __split_huge_page()
error: undefined (user controlled) shift '1 << new_order'
mm/huge_memory.c
2889 static void __split_huge_page(struct page *page, struct list_head *list,
2890 pgoff_t end, unsigned int new_order)
2891 {
2892 struct folio *folio = page_folio(page);
2893 struct page *head = &folio->page;
2894 struct lruvec *lruvec;
2895 struct address_space *swap_cache = NULL;
2896 unsigned long offset = 0;
2897 int i, nr_dropped = 0;
--> 2898 unsigned int new_nr = 1 << new_order;
^^^^^^^^^
The new_order variable comes from the user via debugfs.
2899 int order = folio_order(folio);
2900 unsigned int nr = 1 << order;
2901
2902 /* complete memcg works before add pages to LRU */
2903 split_page_memcg(head, order, new_order);
2904
2905 if (folio_test_anon(folio) && folio_test_swapcache(folio)) {
2906 offset = swp_offset(folio->swap);
2907 swap_cache = swap_address_space(folio->swap);
Here is the debugfs code in split_huge_pages_write()
mm/huge_memory.c
3628
3629 ret = sscanf(input_buf, "%d,0x%lx,0x%lx,%d", &pid, &vaddr_start, &vaddr_end, &new_order);
^^^^^^^^^^
We just read new_order
3630 if (ret == 1 && pid == 1) {
3631 split_huge_pages_all();
3632 ret = strlen(input_buf);
3633 goto out;
3634 } else if (ret != 3 && ret != 4) {
3635 ret = -EINVAL;
3636 goto out;
3637 }
3638
3639 ret = split_huge_pages_pid(pid, vaddr_start, vaddr_end, new_order);
^^^^^^^^^
And pass it directly with no bounds checking. Debugfs code is root
only... We used to take a view that if root does something stupid then
they get what they deserve. But these days syzbot is fuzz testing stuff
even when it's root only and complaining about shift wraps or other
undefined behavior. So I feel like it might be easiest to silence this
undefined behavior warning now instead of waiting for the syzbot reports
to come back to bite us in a couple years.
3640 if (!ret)
3641 ret = strlen(input_buf);
3642 out:
3643 mutex_unlock(&split_debug_mutex);
3644 return ret;
3645
3646 }
regards,
dan carpenter
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [bug report] mm: huge_memory: enable debugfs to split huge pages to any order
2024-03-07 13:49 [bug report] mm: huge_memory: enable debugfs to split huge pages to any order Dan Carpenter
@ 2024-03-07 14:20 ` Zi Yan
2024-03-07 14:31 ` Dan Carpenter
0 siblings, 1 reply; 5+ messages in thread
From: Zi Yan @ 2024-03-07 14:20 UTC (permalink / raw)
To: Dan Carpenter; +Cc: linux-mm
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On 7 Mar 2024, at 8:49, Dan Carpenter wrote:
> Hello Zi Yan,
>
> Commit fc4d182316bd ("mm: huge_memory: enable debugfs to split huge
> pages to any order") from Feb 26, 2024 (linux-next), leads to the
> following Smatch static checker warning:
>
> mm/huge_memory.c:2898 __split_huge_page()
> error: undefined (user controlled) shift '1 << new_order'
>
> mm/huge_memory.c
> 2889 static void __split_huge_page(struct page *page, struct list_head *list,
> 2890 pgoff_t end, unsigned int new_order)
> 2891 {
> 2892 struct folio *folio = page_folio(page);
> 2893 struct page *head = &folio->page;
> 2894 struct lruvec *lruvec;
> 2895 struct address_space *swap_cache = NULL;
> 2896 unsigned long offset = 0;
> 2897 int i, nr_dropped = 0;
> --> 2898 unsigned int new_nr = 1 << new_order;
> ^^^^^^^^^
> The new_order variable comes from the user via debugfs.
>
> 2899 int order = folio_order(folio);
> 2900 unsigned int nr = 1 << order;
> 2901
> 2902 /* complete memcg works before add pages to LRU */
> 2903 split_page_memcg(head, order, new_order);
> 2904
> 2905 if (folio_test_anon(folio) && folio_test_swapcache(folio)) {
> 2906 offset = swp_offset(folio->swap);
> 2907 swap_cache = swap_address_space(folio->swap);
>
> Here is the debugfs code in split_huge_pages_write()
>
> mm/huge_memory.c
> 3628
> 3629 ret = sscanf(input_buf, "%d,0x%lx,0x%lx,%d", &pid, &vaddr_start, &vaddr_end, &new_order);
> ^^^^^^^^^^
> We just read new_order
>
> 3630 if (ret == 1 && pid == 1) {
> 3631 split_huge_pages_all();
> 3632 ret = strlen(input_buf);
> 3633 goto out;
> 3634 } else if (ret != 3 && ret != 4) {
> 3635 ret = -EINVAL;
> 3636 goto out;
> 3637 }
> 3638
> 3639 ret = split_huge_pages_pid(pid, vaddr_start, vaddr_end, new_order);
> ^^^^^^^^^
> And pass it directly with no bounds checking. Debugfs code is root
> only... We used to take a view that if root does something stupid then
> they get what they deserve. But these days syzbot is fuzz testing stuff
> even when it's root only and complaining about shift wraps or other
> undefined behavior. So I feel like it might be easiest to silence this
> undefined behavior warning now instead of waiting for the syzbot reports
> to come back to bite us in a couple years.
Sure. Thank you for reporting this.
Can you check if the patch below fixes the issue? I checked the inputs from
debugfs and also inside split_huge_page_to_list_to_order().
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a81a09236c16..4d21e57a7d07 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3052,6 +3052,9 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
+ if (new_order >= folio_order(folio))
+ return -EINVAL;
+
/* Cannot split anonymous THP to order-1 */
if (new_order == 1 && folio_test_anon(folio)) {
VM_WARN_ONCE(1, "Cannot split to order-1 folio");
@@ -3484,6 +3487,9 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
goto next;
total++;
+
+ if (new_order >= folio_order(folio))
+ goto next;
/*
* For folios with private, split_huge_page_to_list_to_order()
* will try to drop it before split and then check if the folio
@@ -3550,6 +3556,9 @@ static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
total++;
nr_pages = folio_nr_pages(folio);
+ if (new_order >= folio_order(folio))
+ goto next;
+
if (!folio_trylock(folio))
goto next;
--
Best Regards,
Yan, Zi
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [bug report] mm: huge_memory: enable debugfs to split huge pages to any order
2024-03-07 14:20 ` Zi Yan
@ 2024-03-07 14:31 ` Dan Carpenter
2024-03-07 14:41 ` Zi Yan
0 siblings, 1 reply; 5+ messages in thread
From: Dan Carpenter @ 2024-03-07 14:31 UTC (permalink / raw)
To: Zi Yan; +Cc: linux-mm
On Thu, Mar 07, 2024 at 09:20:09AM -0500, Zi Yan wrote:
>
> Can you check if the patch below fixes the issue? I checked the inputs from
> debugfs and also inside split_huge_page_to_list_to_order().
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index a81a09236c16..4d21e57a7d07 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3052,6 +3052,9 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
> VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
> VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>
> + if (new_order >= folio_order(folio))
> + return -EINVAL;
> +
> /* Cannot split anonymous THP to order-1 */
> if (new_order == 1 && folio_test_anon(folio)) {
> VM_WARN_ONCE(1, "Cannot split to order-1 folio");
From a static analysis perspective I think just this is sufficient? But
I don't really know the code and don't object to the other parts of
this path either.
regards,
dan carpenter
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [bug report] mm: huge_memory: enable debugfs to split huge pages to any order
2024-03-07 14:31 ` Dan Carpenter
@ 2024-03-07 14:41 ` Zi Yan
2024-03-07 14:44 ` Dan Carpenter
0 siblings, 1 reply; 5+ messages in thread
From: Zi Yan @ 2024-03-07 14:41 UTC (permalink / raw)
To: Dan Carpenter; +Cc: linux-mm
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On 7 Mar 2024, at 9:31, Dan Carpenter wrote:
> On Thu, Mar 07, 2024 at 09:20:09AM -0500, Zi Yan wrote:
>>
>> Can you check if the patch below fixes the issue? I checked the inputs from
>> debugfs and also inside split_huge_page_to_list_to_order().
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index a81a09236c16..4d21e57a7d07 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -3052,6 +3052,9 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
>> VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
>> VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>>
>> + if (new_order >= folio_order(folio))
>> + return -EINVAL;
>> +
>> /* Cannot split anonymous THP to order-1 */
>> if (new_order == 1 && folio_test_anon(folio)) {
>> VM_WARN_ONCE(1, "Cannot split to order-1 folio");
>
> From a static analysis perspective I think just this is sufficient? But
> I don't really know the code and don't object to the other parts of
> this path either.
You are right. The other two changes are in debugfs to avoid unnecessary
folio locking operations. They are more like an optimization.
--
Best Regards,
Yan, Zi
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [bug report] mm: huge_memory: enable debugfs to split huge pages to any order
2024-03-07 14:41 ` Zi Yan
@ 2024-03-07 14:44 ` Dan Carpenter
0 siblings, 0 replies; 5+ messages in thread
From: Dan Carpenter @ 2024-03-07 14:44 UTC (permalink / raw)
To: Zi Yan; +Cc: linux-mm
On Thu, Mar 07, 2024 at 09:41:17AM -0500, Zi Yan wrote:
> On 7 Mar 2024, at 9:31, Dan Carpenter wrote:
>
> > On Thu, Mar 07, 2024 at 09:20:09AM -0500, Zi Yan wrote:
> >>
> >> Can you check if the patch below fixes the issue? I checked the inputs from
> >> debugfs and also inside split_huge_page_to_list_to_order().
> >>
> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> >> index a81a09236c16..4d21e57a7d07 100644
> >> --- a/mm/huge_memory.c
> >> +++ b/mm/huge_memory.c
> >> @@ -3052,6 +3052,9 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
> >> VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
> >> VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
> >>
> >> + if (new_order >= folio_order(folio))
> >> + return -EINVAL;
> >> +
> >> /* Cannot split anonymous THP to order-1 */
> >> if (new_order == 1 && folio_test_anon(folio)) {
> >> VM_WARN_ONCE(1, "Cannot split to order-1 folio");
> >
> > From a static analysis perspective I think just this is sufficient? But
> > I don't really know the code and don't object to the other parts of
> > this path either.
>
> You are right. The other two changes are in debugfs to avoid unnecessary
> folio locking operations. They are more like an optimization.
Fantastic. Thanks!
regards,
dan carpenter
^ permalink raw reply [flat|nested] 5+ messages in thread
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2024-03-07 13:49 [bug report] mm: huge_memory: enable debugfs to split huge pages to any order Dan Carpenter
2024-03-07 14:20 ` Zi Yan
2024-03-07 14:31 ` Dan Carpenter
2024-03-07 14:41 ` Zi Yan
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