lkml.org 
[lkml]   [2022]   [May]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v3] mm: page_frag: Warn_on when frag_alloc size is bigger than PAGE_SIZE
Date
netdev_alloc_frag->page_frag_alloc may cause memory corruption in 
the following process:

1. A netdev_alloc_frag function call need alloc 200 Bytes to build a skb.

2. Insufficient memory to alloc PAGE_FRAG_CACHE_MAX_ORDER(32K) in
__page_frag_cache_refill to fill frag cache, then one page(eg:4K)
is allocated, now current frag cache is 4K, alloc is success,
nc->pagecnt_bias--.

3. Then this 200 bytes skb in step 1 is freed, page->_refcount--.

4. Another netdev_alloc_frag function call need alloc 5k, page->_refcount
is equal to nc->pagecnt_bias, reset page count bias and offset to
start of new frag. page_frag_alloc will return the 4K memory for a
5K memory request.

5. The caller write on the extra 1k memory which is not actual allocated
will cause memory corruption.

page_frag_alloc is for fragmented allocation. We should warn the caller
to avoid memory corruption.

When fragsz is larger than one page, we report the failure and return.
I don't think it is a good idea to make efforts to support the
allocation of more than one page in this function because the total
frag cache size(PAGE_FRAG_CACHE_MAX_SIZE 32768) is relatively small.
When the request is larger than one page, the caller should switch to
use other kernel interfaces, such as kmalloc and alloc_Pages.

This bug is mainly caused by the reuse of the previously allocated
frag cache memory by the following LARGER allocations. This bug existed
before page_frag_alloc was ported from __netdev_alloc_frag in
net/core/skbuff.c, so most Linux versions have this problem.

Signed-off-by: Chen Lin <chen45464546@163.com>
---
mm/page_alloc.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e008a3d..ffc42b5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5574,6 +5574,15 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
struct page *page;
int offset;

+ /*
+ * frag_alloc is not suitable for memory alloc which fragsz
+ * is bigger than PAGE_SIZE, use kmalloc or alloc_pages instead.
+ */
+ if (WARN_ONCE(fragz > PAGE_SIZE,
+ "alloc fragsz(%d) > PAGE_SIZE(%ld) not supported, alloc fail\n",
+ fragsz, PAGE_SIZE))
+ return NULL;
+
if (unlikely(!nc->va)) {
refill:
page = __page_frag_cache_refill(nc, gfp_mask);
--
1.7.9.5
\
 
 \ /
  Last update: 2022-05-31 16:46    [W:0.224 / U:0.036 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site