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

Andrey Skvortsov
2024-09-23T16:48:53Z

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

--
2.45.2