linux-kernel - [PATCH 2/3] zram: do not use copy_page with non-page alinged address

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Date:   Thu, 13 Apr 2017 09:17:01 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        <kernel-team@....com>, Minchan Kim <minchan@...nel.org>,
        <stable@...r.kernel.org>
Subject: [PATCH 2/3] zram: do not use copy_page with non-page alinged address

The copy_page is optimized memcpy for page-alinged address.
If it is used with non-page aligned address, it can corrupt memory which
means system corruption. With zram, it can happen with

1. 64K architecture
2. partial IO
3. slub debug

Partial IO need to allocate a page and zram allocates it via kmalloc.
With slub debug, kmalloc(PAGE_SIZE) doesn't return page-size aligned
address. And finally, copy_page(mem, cmem) corrupts memory.

So, this patch changes it to memcpy.

Acutaully, we don't need to change zram_bvec_write part because zsmalloc
returns page-aligned address in case of PAGE_SIZE class but it's not
good to rely on the internal of zsmalloc.

Note:
When this patch is merged to stable, clear_page should be fixed, too.
Unfortunately, recent zram removes it by "same page merge" feature
so it's hard to backport this patch to -stable tree.

I will handle it when I receive the mail from stable tree maintainer
to merge this patch to backport.

Fixes: 42e99bd ("zram: optimize memory operations with clear_page()/copy_page()")
Cc: stable@...r.kernel.org
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 drivers/block/zram/zram_drv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 83c38a123242..11cc8767af99 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -525,7 +525,7 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)

 	cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_RO);
 	if (size == PAGE_SIZE) {
-		copy_page(mem, cmem);
+		memcpy(mem, cmem, PAGE_SIZE);
 	} else {
 		struct zcomp_strm *zstrm = zcomp_stream_get(zram->comp);

@@ -719,7 +719,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,

 	if ((clen == PAGE_SIZE) && !is_partial_io(bvec)) {
 		src = kmap_atomic(page);
-		copy_page(cmem, src);
+		memcpy(cmem, src, PAGE_SIZE);
 		kunmap_atomic(src);
 	} else {
 		memcpy(cmem, src, clen);
-- 
2.7.4