* [PATCH V2] mm: prevent page_frag_alloc() from corrupting the memory
@ 2022-07-13 15:01 Maurizio Lombardi
2022-07-13 15:12 ` Alexander Duyck
2022-07-13 15:45 ` Andrew Morton
0 siblings, 2 replies; 3+ messages in thread
From: Maurizio Lombardi @ 2022-07-13 15:01 UTC (permalink / raw)
To: alexander.duyck; +Cc: kuba, akpm, linux-mm, linux-kernel, netdev, chen45464546
A number of drivers call page_frag_alloc() with a
fragment's size > PAGE_SIZE.
In low memory conditions, __page_frag_cache_refill() may fail the order 3
cache allocation and fall back to order 0;
In this case, the cache will be smaller than the fragment, causing
memory corruptions.
Prevent this from happening by checking if the newly allocated cache
is large enough for the fragment; if not, the allocation will fail
and page_frag_alloc() will return NULL.
V2: do not free the cache page because this could make memory pressure
even worse, just return NULL.
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
---
mm/page_alloc.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e008a3df0485..b1407254a826 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5617,6 +5617,8 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
/* reset page count bias and offset to start of new frag */
nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
offset = size - fragsz;
+ if (unlikely(offset < 0))
+ return NULL;
}
nc->pagecnt_bias--;
--
2.31.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH V2] mm: prevent page_frag_alloc() from corrupting the memory
2022-07-13 15:01 [PATCH V2] mm: prevent page_frag_alloc() from corrupting the memory Maurizio Lombardi
@ 2022-07-13 15:12 ` Alexander Duyck
2022-07-13 15:45 ` Andrew Morton
1 sibling, 0 replies; 3+ messages in thread
From: Alexander Duyck @ 2022-07-13 15:12 UTC (permalink / raw)
To: Maurizio Lombardi
Cc: Jakub Kicinski, Andrew Morton, linux-mm, LKML, Netdev, Chen Lin
On Wed, Jul 13, 2022 at 8:01 AM Maurizio Lombardi <mlombard@redhat.com> wrote:
>
> A number of drivers call page_frag_alloc() with a
> fragment's size > PAGE_SIZE.
> In low memory conditions, __page_frag_cache_refill() may fail the order 3
> cache allocation and fall back to order 0;
> In this case, the cache will be smaller than the fragment, causing
> memory corruptions.
>
> Prevent this from happening by checking if the newly allocated cache
> is large enough for the fragment; if not, the allocation will fail
> and page_frag_alloc() will return NULL.
>
> V2: do not free the cache page because this could make memory pressure
> even worse, just return NULL.
>
> Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
> ---
> mm/page_alloc.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e008a3df0485..b1407254a826 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5617,6 +5617,8 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
> /* reset page count bias and offset to start of new frag */
> nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
> offset = size - fragsz;
> + if (unlikely(offset < 0))
> + return NULL;
> }
>
> nc->pagecnt_bias--;
This works for me. If I am not mistaken it should be only adding one
conditional jump that isn't taken to the fast path based on a
calculation we were already doing.
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH V2] mm: prevent page_frag_alloc() from corrupting the memory
2022-07-13 15:01 [PATCH V2] mm: prevent page_frag_alloc() from corrupting the memory Maurizio Lombardi
2022-07-13 15:12 ` Alexander Duyck
@ 2022-07-13 15:45 ` Andrew Morton
1 sibling, 0 replies; 3+ messages in thread
From: Andrew Morton @ 2022-07-13 15:45 UTC (permalink / raw)
To: Maurizio Lombardi
Cc: alexander.duyck, kuba, linux-mm, linux-kernel, netdev, chen45464546
On Wed, 13 Jul 2022 17:01:43 +0200 Maurizio Lombardi <mlombard@redhat.com> wrote:
> A number of drivers call page_frag_alloc() with a
> fragment's size > PAGE_SIZE.
> In low memory conditions, __page_frag_cache_refill() may fail the order 3
> cache allocation and fall back to order 0;
> In this case, the cache will be smaller than the fragment, causing
> memory corruptions.
>
> Prevent this from happening by checking if the newly allocated cache
> is large enough for the fragment; if not, the allocation will fail
> and page_frag_alloc() will return NULL.
>
> ...
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5617,6 +5617,8 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
> /* reset page count bias and offset to start of new frag */
> nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
> offset = size - fragsz;
> + if (unlikely(offset < 0))
> + return NULL;
> }
>
> nc->pagecnt_bias--;
I think we should have a comment here explaining (at least) why we'd
bale after a successful allocation and explaining why we don't call
free_the_page().
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-07-13 15:01 [PATCH V2] mm: prevent page_frag_alloc() from corrupting the memory Maurizio Lombardi
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