linux-kernel - [PATCH] mm: prevent page_frag_alloc() from corrupting the memory

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Message-Id: <20220713145854.147356-1-mlombard@redhat.com>
Date:   Wed, 13 Jul 2022 16:58:54 +0200
From:   Maurizio Lombardi <mlombard@...hat.com>
To:     alexander.duyck@...il.com
Cc:     kuba@...nel.org, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        chen45464546@....com
Subject: [PATCH] mm: prevent page_frag_alloc() from corrupting the memory

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@...hat.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