CVE-2026-90189

Published Sep 17, 2026

Description

In the Linux kernel, the following vulnerability has been resolved: null_blk: register configfs subsystem after creating default devices 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.

Is your site exposed to CVE-2026-90189?

Run a free security scan — no signup, results in seconds.

References

Frequently Asked Questions

What is CVE-2026-90189? +
In the Linux kernel, the following vulnerability has been resolved: null_blk: register configfs subsystem after creating default devices 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.
How do I check if I'm vulnerable to CVE-2026-90189? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Don't wait for an exploit

Scan your website for vulnerabilities like CVE-2026-90189 — free, no signup required.