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

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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@xxxxxxxxx>
Fixes: 684826f8271a ("zram: free secondary algorithms names")
Cc: <stable@xxxxxxxxxxxxxxx>
---

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;
  	}





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