CVE-2026-46079

In the Linux kernel, the following vulnerability has been resolved:

rbd: fix null-ptr-deref when device_add_disk() fails

do_rbd_add() publishes the device with device_add() before calling

device_add_disk(). If device_add_disk() fails after device_add()

succeeds, the error path calls rbd_free_disk() directly and then later

falls through to rbd_dev_device_release(), which calls rbd_free_disk()

again. This double teardown can leave blk-mq cleanup operating on

invalid state and trigger a null-ptr-deref in

__blk_mq_free_map_and_rqs(), reached from blk_mq_free_tag_set().

Fix this by following the normal remove ordering: call device_del()

before rbd_dev_device_release() when device_add_disk() fails after

device_add(). That keeps the teardown sequence consistent and avoids

re-entering disk cleanup through the wrong path.

The bug was first flagged by an experimental analysis tool we are

developing for kernel memory-management bugs while analyzing

v6.13-rc1. The tool is still under development and is not yet publicly

available.

We reproduced the bug on v7.0 with a real Ceph backend and a QEMU x86_64

guest booted with KASAN and CONFIG_FAILSLAB enabled. The reproducer

confines failslab injections to the __add_disk() range and injects

fail-nth while mapping an RBD image through

/sys/bus/rbd/add_single_major.

On the unpatched kernel, fail-nth=4 reliably triggered the fault:

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI

KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]

CPU: 0 UID: 0 PID: 273 Comm: bash Not tainted 7.0.0-01247-gd60bc1401583 #6 PREEMPT(lazy)

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014

RIP: 0010:__blk_mq_free_map_and_rqs+0x8c/0x240

Code: 00 00 48 8b 6b 60 41 89 f4 49 c1 e4 03 4c 01 e5 45 85 ed 0f 85 0a 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 e9 48 c1 e9 03 <80> 3c 01 00 0f 85 31 01 00 00 4c 8b 6d 00 4d 85 ed 0f 84 e2 00 00

RSP: 0018:ff1100000ab0fac8 EFLAGS: 00000246

RAX: dffffc0000000000 RBX: ff1100000c4806a0 RCX: 0000000000000000

RDX: 0000000000000002 RSI: 0000000000000000 RDI: ff1100000c4806f4

RBP: 0000000000000000 R08: 0000000000000001 R09: ffe21c000189001b

R10: ff1100000c4800df R11: ff1100006cf37be0 R12: 0000000000000000

R13: 0000000000000000 R14: ff1100000c480700 R15: ff1100000c480004

FS: 00007f0fbe8fe740(0000) GS:ff110000e5851000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007fe53473b2e0 CR3: 0000000012eef000 CR4: 00000000007516f0

PKRU: 55555554

Call Trace:

<TASK>

blk_mq_free_tag_set+0x77/0x460

do_rbd_add+0x1446/0x2b80

? __pfx_do_rbd_add+0x10/0x10

? lock_acquire+0x18c/0x300

? find_held_lock+0x2b/0x80

? sysfs_file_kobj+0xb6/0x1b0

? __pfx_sysfs_kf_write+0x10/0x10

kernfs_fop_write_iter+0x2f4/0x4a0

vfs_write+0x98e/0x1000

? expand_files+0x51f/0x850

? __pfx_vfs_write+0x10/0x10

ksys_write+0xf2/0x1d0

? __pfx_ksys_write+0x10/0x10

do_syscall_64+0x115/0x690

entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7f0fbea15907

Code: 10 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24

RSP: 002b:00007ffe22346ea8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001

RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007f0fbea15907

RDX: 0000000000000058 RSI: 0000563ace6c0ef0 RDI: 0000000000000001

RBP: 0000563ace6c0ef0 R08: 0000563ace6c0ef0 R09: 6b6435726d694141

R10: 5250337279762f78 R11: 0000000000000246 R12: 0000000000000058

R13: 00007f0fbeb1c780 R14: ff1100000c480700 R15: ff1100000c480004

</TASK>

With this fix applied, rerunning the reproducer over fail-nth=1..256

yields no KASAN reports.

[ idryomov: rename err_out_device_del -> err_out_device ]