6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Zizhi Wo <redacted>
[ Upstream commit c9d293d6bb0575fcb1f3408129453187e2a28a4e ]
In null_init(), configfs_register_subsystem() currently runs before
register_blkdev(), so when null_blk is built as a module, a racing mkdir()
+ poweron from userspace can reach null_add_dev() while null_major is still
0. __add_disk() then hits WARN_ON(disk->minors) (major=0 with minors!=0)
and fails:
[root@fedora ~]# [ 2366.521436] WARNING: block/genhd.c:476 at __add_disk+0x8a7/0xde0,
[ 2366.523552] Modules linked in: null_blk(+) nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib
[ 2366.529081] CPU: 26 UID: 0 PID: 1600 Comm: sh Not tainted 7.2.0-rc1+ #66 PREEMPT(full)
......
[ 2366.547251] Call Trace:
[ 2366.547575] <TASK>
[ 2366.547831] ? _raw_spin_lock+0x84/0xe0
[ 2366.548260] add_disk_fwnode+0x114/0x560
[ 2366.548739] null_add_dev+0x102d/0x1b80 [null_blk]
[ 2366.549310] ? __pfx_null_add_dev+0x10/0x10 [null_blk]
[ 2366.549906] ? mutex_lock+0xde/0x1c0
[ 2366.550361] ? __pfx_mutex_lock+0x10/0x10
[ 2366.550827] nullb_device_power_store+0x1e7/0x280 [null_blk]
[ 2366.551499] ? __pfx_nullb_device_power_store+0x10/0x10 [null_blk]
[ 2366.552177] ? __kmalloc_cache_noprof+0x1f5/0x470
[ 2366.552748] ? configfs_write_iter+0x35c/0x4e0
[ 2366.553242] configfs_write_iter+0x286/0x4e0
[ 2366.553787] vfs_write+0x52d/0xd00
[ 2366.554169] ? __pfx_vfs_write+0x10/0x10
[ 2366.554679] ? __pfx___css_rstat_updated+0x10/0x10
[ 2366.555196] ? fdget_pos+0x1cf/0x4c0
[ 2366.555649] ksys_write+0xfc/0x1d0
......
Additionally, the err_dev path destroys all devices on nullb_list while
configfs is still registered. If a racing mkdir() + poweron puts a user
device on the list, null_destroy_dev()->null_free_dev() kfrees the user
device's nullb_device but /sys/kernel/config/nullb/<name> is still
reachable. Any userspace access to the item will trigger a UAF.
For simplicity, move configfs_register_subsystem() to the end to solve
the problems above.
Fixes: 3bf2bd20734e ("nullb: add configfs interface")
Signed-off-by: Zizhi Wo <redacted>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Nilay Shroff <redacted>
Link: https://patch.msgid.link/20260725022509.714271-3-wozizhi@huaweicloud.com (local)
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/block/null_blk/main.c | 16 ++++++----------
1 file changed, 6 insertions(+), 10 deletions(-)
diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 11bda1242283b..d7e4a0be125af 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -2284,15 +2284,9 @@ static int __init null_init(void)
config_group_init(&nullb_subsys.su_group);
mutex_init(&nullb_subsys.su_mutex);
- ret = configfs_register_subsystem(&nullb_subsys);
- if (ret)
- return ret;
-
null_major = register_blkdev(0, "nullb");
- if (null_major < 0) {
- ret = null_major;
- goto err_conf;
- }
+ if (null_major < 0)
+ return null_major;
for (i = 0; i < nr_devices; i++) {
ret = null_create_dev();@@ -2300,6 +2294,10 @@ static int __init null_init(void)
goto err_dev;
}
+ ret = configfs_register_subsystem(&nullb_subsys);
+ if (ret)
+ goto err_dev;
+
pr_info("module loaded\n");
return 0;
@@ -2309,8 +2307,6 @@ static int __init null_init(void)
null_destroy_dev(nullb);
}
unregister_blkdev(null_major, "nullb");
-err_conf:
- configfs_unregister_subsystem(&nullb_subsys);
return ret;
}
--
2.53.0