Re: FAILED: patch "[PATCH] zram: do not use copy_page with non-page aligned address" failed to apply to 3.18-stable tree

[Minchan Kim <minchan@kernel.org>]

On Tue, Apr 18, 2017 at 02:18:28PM +0200, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 3.18-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> thanks,
> 
> greg k-h

Hi Greg,

I backported this patch for v3.18.49. Could you merge this?
Sergey, could you review this?

>From 042b3d57120146ab24b284713d44a9c1b37935b3 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Wed, 19 Apr 2017 09:28:39 +0900
Subject: [PATCH for v3.18] zram: do not use copy_page with non-page aligned address

commit d72e9a7a93e4f8e9e52491921d99e0c8aa89eb4e upstream

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/memset.

Actuaully, 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.

And I didn't change clear_page in handle_zero_page intentionally because
it's very clear no problem because kmap_atomic guarantees address
is page-size alinged.

Fixes: 42e99bd ("zram: optimize memory operations with clear_page()/copy_page()")
Link: http://lkml.kernel.org/r/1492042622-12074-2-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: <stable@vger.kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 drivers/block/zram/zram_drv.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 3920ee45aa59..7e94459a489a 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -431,13 +431,13 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
 
 	if (!handle || zram_test_flag(meta, index, ZRAM_ZERO)) {
 		bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
-		clear_page(mem);
+		memset(mem, 0, PAGE_SIZE);
 		return 0;
 	}
 
 	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
 		ret = zcomp_decompress(zram->comp, cmem, size, mem);
 	zs_unmap_object(meta->mem_pool, handle);
@@ -612,7 +612,7 @@ 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