Patch "zram: do not use copy_page with non-page aligned address" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

zram: do not use copy_page with non-page aligned address

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
zram-do-not-use-copy_page-with-non-page-aligned-address.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Minchan Kim <[email protected]>
Date: Thu, 13 Apr 2017 14:56:37 -0700
Subject: zram: do not use copy_page with non-page aligned address

From: Minchan Kim <[email protected]>

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.

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.

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.

---
 drivers/block/zram/zram_drv.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

@@ -574,13 +574,13 @@ static int zram_decompress_page(struct z
 
 	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);

@@ -738,7 +738,7 @@ static int zram_bvec_write(struct zram *
 
 	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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/zram-do-not-use-copy_page-with-non-page-aligned-address.patch