Re: [PATCH] bcache: Revert "bcache: use bvec_virt"

From: Coly Li <colyli@suse.de>
To: axboe@kernel.dk
Cc: linux-bcache@vger.kernel.org, linux-block@vger.kernel.org,
	Christoph Hellwig <hch@lst.de>,
	stable@vger.kernel.org
Subject: Re: [PATCH] bcache: Revert "bcache: use bvec_virt"
Date: Mon, 8 Nov 2021 16:16:51 +0800	[thread overview]
Message-ID: <0bfbf514-4036-23ff-436a-01e0b7eba67e@suse.de> (raw)
In-Reply-To: <20211103151041.70516-1-colyli@suse.de>

On 11/3/21 11:10 PM, Coly Li wrote:
> This reverts commit 2fd3e5efe791946be0957c8e1eed9560b541fe46.
>
> The above commit replaces page_address(bv->bv_page) by bvec_virt(bv) to
> avoid directly access to bv->bv_page, but in situation bv->bv_offset is
> not zero and page_address(bv->bv_page) is not equal to bvec_virt(bv). In
> such case a memory corruption may happen because memory in next page is
> tainted by following line in do_btree_node_write(),
> 	memcpy(bvec_virt(bv), addr, PAGE_SIZE);
>
> This patch reverts the mentioned commit to avoid the memory corruption.
>
> Fixes: 2fd3e5efe791 ("bcache: use bvec_virt")
> Signed-off-by: Coly Li <colyli@suse.de>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: stable@vger.kernel.org # 5.15
> ---
>   drivers/md/bcache/btree.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> index 93b67b8d31c3..88c573eeb598 100644
> --- a/drivers/md/bcache/btree.c
> +++ b/drivers/md/bcache/btree.c
> @@ -378,7 +378,7 @@ static void do_btree_node_write(struct btree *b)
>   		struct bvec_iter_all iter_all;
>   
>   		bio_for_each_segment_all(bv, b->bio, iter_all) {
> -			memcpy(bvec_virt(bv), addr, PAGE_SIZE);
> +			memcpy(page_address(bv->bv_page), addr, PAGE_SIZE);
>   			addr += PAGE_SIZE;
>   		}
>   

Hi Jens,

Since now we don't have a better alternative patch yet, and this issue 
should be fixed ASAP. Could you please take it firstly. And I will work 
with Christoph for a better change (maybe large and not trivial) later 
for next merge window?

Thanks.

Coly Li