linux-kernel - Re: [PATCH] zram: don't call idr_remove() from zram

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Date:	Fri, 15 Jan 2016 09:43:17 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Jerome Marchand <jmarchan@...hat.com>
Cc:	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zram: don't call idr_remove() from zram_remove()

Cc Andrew

On (01/14/16 14:03), Jerome Marchand wrote:
> The use of idr_remove() is forbidden in the callback functions of
> idr_for_each(). It is therefore unsafe to call idr_remove in
> zram_remove().
> This patch moves the call to idr_remove() from zram_remove() to
> hot_remove_store(). In the detroy_devices() path, idrs are removed by
> idr_destroy().
> This solves an use-after-free detected by KASan.

thanks, good catch! wow, I must be blind or stupid, or both.


Acked-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

a nano nitpick to add curly braces in the else clause.
but, what is more important, may I please ask you to add -stable [4.2+]

> Signed-off-by: Jerome Marchand <jmarchan@...hat.com>
+ Cc: <stable@...r.kernel.org>

and to resend the patch?



idr added in 4.2
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/drivers/block/zram/zram_drv.c?id=refs/tags/v4.2

	-ss

> ---
>  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 47915d7..5e86e1d 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1325,7 +1325,6 @@ static int zram_remove(struct zram *zram)
>  
>  	pr_info("Removed device: %s\n", zram->disk->disk_name);
>  
> -	idr_remove(&zram_index_idr, zram->disk->first_minor);
>  	blk_cleanup_queue(zram->disk->queue);
>  	del_gendisk(zram->disk);
>  	put_disk(zram->disk);
> @@ -1367,9 +1366,10 @@ static ssize_t hot_remove_store(struct class *class,
>  	mutex_lock(&zram_index_mutex);
>  
>  	zram = idr_find(&zram_index_idr, dev_id);
> -	if (zram)
> +	if (zram) {
>  		ret = zram_remove(zram);
> -	else
> +		idr_remove(&zram_index_idr, dev_id);

+	} else {
>  		ret = -ENODEV;
+	}


>  	mutex_unlock(&zram_index_mutex);
> -- 
> 2.5.0
>