linux-kernel - Re: [PATCH v3] zram: don't free statically defined names

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Message-ID: <c8a4e62e-6c24-4b06-ac86-64cc4697bc2f@wanadoo.fr>
Date: Mon, 23 Sep 2024 19:40:27 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Andrey Skvortsov <andrej.skvortzov@...il.com>,
 Venkat Rao Bagalkote <venkat88@...ux.vnet.ibm.com>,
 Minchan Kim <minchan@...nel.org>,
 Sergey Senozhatsky <senozhatsky@...omium.org>, Jens Axboe <axboe@...nel.dk>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
 linux-block@...r.kernel.org
Cc: stable@...r.kernel.org
Subject: Re: [PATCH v3] zram: don't free statically defined names

Le 23/09/2024 à 18:48, Andrey Skvortsov a écrit :
> When CONFIG_ZRAM_MULTI_COMP isn't set ZRAM_SECONDARY_COMP can hold
> default_compressor, because it's the same offset as ZRAM_PRIMARY_COMP,
> so we need to make sure that we don't attempt to kfree() the
> statically defined compressor name.
> 
> This is detected by KASAN.
> 
> ==================================================================
>    Call trace:
>     kfree+0x60/0x3a0
>     zram_destroy_comps+0x98/0x198 [zram]
>     zram_reset_device+0x22c/0x4a8 [zram]
>     reset_store+0x1bc/0x2d8 [zram]
>     dev_attr_store+0x44/0x80
>     sysfs_kf_write+0xfc/0x188
>     kernfs_fop_write_iter+0x28c/0x428
>     vfs_write+0x4dc/0x9b8
>     ksys_write+0x100/0x1f8
>     __arm64_sys_write+0x74/0xb8
>     invoke_syscall+0xd8/0x260
>     el0_svc_common.constprop.0+0xb4/0x240
>     do_el0_svc+0x48/0x68
>     el0_svc+0x40/0xc8
>     el0t_64_sync_handler+0x120/0x130
>     el0t_64_sync+0x190/0x198
> ==================================================================
> 
> Signed-off-by: Andrey Skvortsov <andrej.skvortzov@...il.com>
> Fixes: 684826f8271a ("zram: free secondary algorithms names")
> Cc: <stable@...r.kernel.org>
> ---
> 
> Changes in v2:
>   - removed comment from source code about freeing statically defined compression
>   - removed part of KASAN report from commit description
>   - added information about CONFIG_ZRAM_MULTI_COMP into commit description
> 
> Changes in v3:
>   - modified commit description based on Sergey's comment
>   - changed start for-loop to ZRAM_PRIMARY_COMP
> 
> 
>   drivers/block/zram/zram_drv.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index c3d245617083d..ad9c9bc3ccfc5 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -2115,8 +2115,10 @@ static void zram_destroy_comps(struct zram *zram)
>   		zram->num_active_comps--;
>   	}
>   
> -	for (prio = ZRAM_SECONDARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
> -		kfree(zram->comp_algs[prio]);
> +	for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
> +		/* Do not free statically defined compression algorithms */
> +		if (zram->comp_algs[prio] != default_compressor)
> +			kfree(zram->comp_algs[prio]);

Hi,

maybe kfree_const() to be more future proof and less verbose?

CJ

>   		zram->comp_algs[prio] = NULL;
>   	}
>