linux-kernel - Re: [PATCH] zram: unsafe zram_get_element call in zram_read

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20231107073911.GB11577@google.com>
Date:   Tue, 7 Nov 2023 16:39:11 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        zhouxianrong <zhouxianrong@...wei.com>,
        Vasily Averin <vasily.averin@...ux.dev>
Subject: Re: [PATCH] zram: unsafe zram_get_element call in zram_read_page()

On (23/11/06 22:54), Vasily Averin wrote:
> @@ -1362,14 +1362,14 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
>  		ret = zram_read_from_zspool(zram, page, index);
>  		zram_slot_unlock(zram, index);
>  	} else {
> +		unsigned long entry = zram_get_element(zram, index);
>  		/*
>  		 * The slot should be unlocked before reading from the backing
>  		 * device.
>  		 */
>  		zram_slot_unlock(zram, index);
>  
> -		ret = read_from_bdev(zram, page, zram_get_element(zram, index),
> -				     parent);
> +		ret = read_from_bdev(zram, page, entry, parent);

Hmmm,
We may want to do more here. Basically, we probably need to re-confirm
after read_from_bdev() that the entry at index still has ZRAM_WB set
and, if so, that it points to the same blk_idx. IOW, check that it has
not been free-ed and re-used under us.

Minchan, what do you think? Is that scenario possible?