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Subject[PATCH] mm: prevent page_frag_alloc() from corrupting the memory
Date
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
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