The patch titled
Subject: zram: fix NULL pointer in comp_algorithm_show()
has been added to the -mm mm-unstable branch. Its filename is
zram-fix-null-pointer-in-comp_algorithm_show.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-fix-null-pointer-in-comp_algorithm_show.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Liu Shixin <liushixin2@xxxxxxxxxx>
Subject: zram: fix NULL pointer in comp_algorithm_show()
Date: Fri, 8 Nov 2024 18:01:47 +0800
LTP reported a NULL pointer dereference as followed:
CPU: 7 UID: 0 PID: 5995 Comm: cat Kdump: loaded Not tainted 6.12.0-rc6+ #3
Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
pstate: 40400005 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : __pi_strcmp+0x24/0x140
lr : zcomp_available_show+0x60/0x100 [zram]
sp : ffff800088b93b90
x29: ffff800088b93b90 x28: 0000000000000001 x27: 0000000000400cc0
x26: 0000000000000ffe x25: ffff80007b3e2388 x24: 0000000000000000
x23: ffff80007b3e2390 x22: ffff0004041a9000 x21: ffff80007b3e2900
x20: 0000000000000000 x19: 0000000000000000 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000000 x10: ffff80007b3e2900 x9 : ffff80007b3cb280
x8 : 0101010101010101 x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000040 x4 : 0000000000000000 x3 : 00656c722d6f7a6c
x2 : 0000000000000000 x1 : ffff80007b3e2900 x0 : 0000000000000000
Call trace:
__pi_strcmp+0x24/0x140
comp_algorithm_show+0x40/0x70 [zram]
dev_attr_show+0x28/0x80
sysfs_kf_seq_show+0x90/0x140
kernfs_seq_show+0x34/0x48
seq_read_iter+0x1d4/0x4e8
kernfs_fop_read_iter+0x40/0x58
new_sync_read+0x9c/0x168
vfs_read+0x1a8/0x1f8
ksys_read+0x74/0x108
__arm64_sys_read+0x24/0x38
invoke_syscall+0x50/0x120
el0_svc_common.constprop.0+0xc8/0xf0
do_el0_svc+0x24/0x38
el0_svc+0x38/0x138
el0t_64_sync_handler+0xc0/0xc8
el0t_64_sync+0x188/0x190
The zram->comp_algs[ZRAM_PRIMARY_COMP] can be NULL in zram_add() if
comp_algorithm_set() has not been called. User can access the zram device
by sysfs after device_add_disk(), so there is a time window to trigger the
NULL pointer dereference. Move it ahead device_add_disk() to make sure
when user can access the zram device, it is ready. comp_algorithm_set()
is protected by zram->init_lock in other places and no such problem.
Link: https://lkml.kernel.org/r/20241108100147.3776123-1-liushixin2@xxxxxxxxxx
Fixes: 7ac07a26dea7 ("zram: preparation for multi-zcomp support")
Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
--- a/drivers/block/zram/zram_drv.c~zram-fix-null-pointer-in-comp_algorithm_show
+++ a/drivers/block/zram/zram_drv.c
@@ -2572,6 +2572,8 @@ static int zram_add(void)
zram->disk->private_data = zram;
snprintf(zram->disk->disk_name, 16, "zram%d", device_id);
atomic_set(&zram->pp_in_progress, 0);
+ zram_comp_params_reset(zram);
+ comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);
/* Actual capacity set using sysfs (/sys/block/zram<id>/disksize */
set_capacity(zram->disk, 0);
@@ -2579,9 +2581,6 @@ static int zram_add(void)
if (ret)
goto out_cleanup_disk;
- zram_comp_params_reset(zram);
- comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);
-
zram_debugfs_register(zram);
pr_info("Added device: %s\n", zram->disk->disk_name);
return device_id;
_
Patches currently in -mm which might be from liushixin2@xxxxxxxxxx are
zram-fix-null-pointer-in-comp_algorithm_show.patch
