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

Andrey Skvortsov
2024-09-23T22:41:51Z

On 24-09-23 19:40, Christophe JAILLET wrote:
> 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?

kfree_const() will not work if zram is built as a module. It works
only for .rodata for kernel image. [1]

1. https://elixir.bootlin.com/linux/v6.11/source/include/asm-generic/sections.h#L177

--
Best regards,
Andrey Skvortsov