[PATCH 5.4 12/30] mm: prevent page_frag_alloc() from corrupting the memory - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Maurizio Lombardi <mlombard@redhat.com>,
	Alexander Duyck <alexanderduyck@fb.com>,
	Chen Lin <chen45464546@163.com>, Jakub Kicinski <kuba@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: [PATCH 5.4 12/30] mm: prevent page_frag_alloc() from corrupting the memory
Date: Mon,  3 Oct 2022 09:11:54 +0200	[thread overview]
Message-ID: <20221003070716.648085562@linuxfoundation.org> (raw)
In-Reply-To: <20221003070716.269502440@linuxfoundation.org>

From: Maurizio Lombardi <mlombard@redhat.com>

commit dac22531bbd4af2426c4e29e05594415ccfa365d upstream.

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.

Link: https://lkml.kernel.org/r/20220715125013.247085-1-mlombard@redhat.com
Fixes: b63ae8ca096d ("mm/net: Rename and move page fragment handling from net/ to mm/")
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Cc: Chen Lin <chen45464546@163.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/page_alloc.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4979,6 +4979,18 @@ refill:
 		/* 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)) {
+			/*
+			 * The caller is trying to allocate a fragment
+			 * with fragsz > PAGE_SIZE but the cache isn't big
+			 * enough to satisfy the request, this may
+			 * happen in low memory conditions.
+			 * We don't release the cache page because
+			 * it could make memory pressure worse
+			 * so we simply return NULL here.
+			 */
+			return NULL;
+		}
 	}
 
 	nc->pagecnt_bias--;


