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

Christophe JAILLET
2024-09-23T17:49:31Z

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@gmail.com>
> Fixes: 684826f8271a ("zram: free secondary algorithms names")
> Cc: <stable@vger.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;
> }
>