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CVE-2026-46079: rbd: fix null-ptr-deref when device_add_disk() fails

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 ]

UnknownCVSS not scoredNot KEV-listedUpdated
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Security readout for executives and security teams

Plain-English summary

CVE-2026-46079 is a Linux kernel RBD driver bug that can crash the kernel during a failed disk-add path. It matters mainly for systems using Ceph RBD block devices. Public sources do not show active exploitation, and no CVSS score is provided.

Executive priority

Patch during the next kernel maintenance window for Ceph RBD infrastructure. Escalate sooner where RBD mapping is common or kernel crashes would disrupt storage-dependent workloads. Current public evidence supports denial-of-service concern, not confirmed active exploitation.

Technical view

The rbd do_rbd_add() path published a device before device_add_disk(). If device_add_disk() failed, cleanup could call rbd_free_disk() twice, leaving blk-mq cleanup with invalid state and causing a null pointer dereference in __blk_mq_free_map_and_rqs(). Stable kernel commits correct teardown ordering with device_del().

Likely exposure

Exposure is most likely on Linux systems using the rbd kernel driver for Ceph RBD mapping. The source lists Linux as affected from 5.16 through multiple stable branches before their fixed commits, including 6.1, 6.6, 6.12, 6.18, 7.0, and 7.1 lines.

Exploitation context

No active exploitation is cited, and KEV is false. The reported reproduction required a real Ceph backend, QEMU guest, KASAN, CONFIG_FAILSLAB, and controlled failure injection while mapping an RBD image, so practical exploitability outside fault-injection conditions is not established.

Researcher notes

The source identifies a double-teardown error path after device_add_disk() failure following device_add(). The fix restores normal remove ordering by calling device_del() before release. Reproduction evidence is strong for the bug, but attacker-controlled reachability and non-lab triggering conditions remain incomplete.

Mitigation direction

  • Update affected Linux kernels to vendor builds containing the referenced stable rbd fix.
  • Prioritize hosts using Ceph RBD block devices or allowing RBD device mapping.
  • If patch status is unclear, check Linux distribution and kernel vendor advisories.
  • Avoid treating fault-injection reproduction details as evidence of real-world exploitation.

Validation and detection

  • Inventory kernel versions and identify systems using the rbd kernel module.
  • Confirm the installed kernel includes one of the referenced stable fix commits or vendor backports.
  • Review kernel logs for rbd add failures, blk-mq cleanup faults, or null pointer dereferences.
  • Track CVE and vendor advisories for later CVSS, affected-version, or mitigation updates.
Prepared
Confidence
medium
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
7Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

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Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux27c97abc30e2b9ad2288977c0ecbef4d50553f57, 27c97abc30e2b9ad2288977c0ecbef4d50553f57, 27c97abc30e2b9ad2288977c0ecbef4d50553f57, 27c97abc30e2b9ad2288977c0ecbef4d50553f57, 27c97abc30e2b9ad2288977c0ecbef4d50553f57, 27c97abc30e2b9ad2288977c0ecbef4d50553f57unaffected
LinuxLinux5.16, 0, 6.1.175, 6.6.140, 6.12.86, 6.18.27, 7.0.4, 7.1affected
Weakness

CWE details

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