CVE-2022-49700

HIGH EPSS 19.4%
Published Feb 26, 20251y ago · Modified Jun 17, 20262w ago
7.8 CVSS 3.1
High
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Published Feb 26, 2025 1y ago
Last Modified Jun 17, 2026 2w ago

Description

In the Linux kernel, the following vulnerability has been resolved: mm/slub: add missing TID updates on slab deactivation The fastpath in slab_alloc_node() assumes that c->slab is stable as long as the TID stays the same. However, two places in __slab_alloc() currently don't update the TID when deactivating the CPU slab. If multiple operations race the right way, this could lead to an object getting lost; or, in an even more unlikely situation, it could even lead to an object being freed onto the wrong slab's freelist, messing up the `inuse` counter and eventually causing a page to be freed to the page allocator while it still contains slab objects. (I haven't actually tested these cases though, this is just based on looking at the code. Writing testcases for this stuff seems like it'd be a pain...) The race leading to state inconsistency is (all operations on the same CPU and kmem_cache): - task A: begin do_slab_free(): - read TID - read pcpu freelist (==NULL) - check `slab == c->slab` (true) - [PREEMPT A->B] - task B: begin slab_alloc_node(): - fastpath fails (`c->freelist` is NULL) - enter __slab_alloc() - slub_get_cpu_ptr() (disables preemption) - enter ___slab_alloc() - take local_lock_irqsave() - read c->freelist as NULL - get_freelist() returns NULL - write `c->slab = NULL` - drop local_unlock_irqrestore() - goto new_slab - slub_percpu_partial() is NULL - get_partial() returns NULL - slub_put_cpu_ptr() (enables preemption) - [PREEMPT B->A] - task A: finish do_slab_free(): - this_cpu_cmpxchg_double() succeeds() - [CORRUPT STATE: c->slab==NULL, c->freelist!=NULL] From there, the object on c->freelist will get lost if task B is allowed to continue from here: It will proceed to the retry_load_slab label, set c->slab, then jump to load_freelist, which clobbers c->freelist. But if we instead continue as follows, we get worse corruption: - task A: run __slab_free() on object from other struct slab: - CPU_PARTIAL_FREE case (slab was on no list, is now on pcpu partial) - task A: run slab_alloc_node() with NUMA node constraint: - fastpath fails (c->slab is NULL) - call __slab_alloc() - slub_get_cpu_ptr() (disables preemption) - enter ___slab_alloc() - c->slab is NULL: goto new_slab - slub_percpu_partial() is non-NULL - set c->slab to slub_percpu_partial(c) - [CORRUPT STATE: c->slab points to slab-1, c->freelist has objects from slab-2] - goto redo - node_match() fails - goto deactivate_slab - existing c->freelist is passed into deactivate_slab() - inuse count of slab-1 is decremented to account for object from slab-2 At this point, the inuse count of slab-1 is 1 lower than it should be. This means that if we free all allocated objects in slab-1 except for one, SLUB will think that slab-1 is completely unused, and may free its page, leading to use-after-free.

CVSS Details

Base Score
7.8
Exploitability
1.8
Impact
5.9
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Attack Vector Local
Attack Complexity Low
Privileges Required Low
User Interaction None
Scope Unchanged
Confidentiality High
Integrity High
Availability High

Threat Intelligence

EPSS Exploit Probability
19.4% percentile
Exploit & Patch Status
No Known Exploit
Patch Available

Weaknesses 1

CWE-416 Use After Free Memory Safety

Affected Products 10

VendorProductVersionRange
linuxlinux_kernel*≥3.1  –  <4.9.323
linuxlinux_kernel*≥4.10  –  <4.14.288
linuxlinux_kernel*≥4.15  –  <4.19.252
linuxlinux_kernel*≥4.20  –  <5.4.205
linuxlinux_kernel*≥5.5  –  <5.10.130
linuxlinux_kernel*≥5.11  –  <5.15.54
linuxlinux_kernel*≥5.16  –  <5.18.8
linuxlinux_kernel5.19any
linuxlinux_kernel5.19any
linuxlinux_kernel5.19any

References 8

  • git.kernel.org https://git.kernel.org/stable/c/0515cc9b6b24877f59b222ade704bfaa42caa2a6
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/197e257da473c725dfe47759c3ee02f2398d8ea5
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/308c6d0e1f200fd26c71270c6e6bfcf0fc6ff082
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/6c32496964da0dc230cea763a0e934b2e02dabd5
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/d6a597450e686d4c6388bd3cdcb17224b4dae7f0
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/e2b2f0e2e34d71ae6c2a1114fd3c525930e84bc7
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/e7e3e90d671078455a3a08189f89d85b3da2de9e
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/eeaa345e128515135ccb864c04482180c08e3259
    Patch

Remediation

  • git.kernel.org https://git.kernel.org/stable/c/0515cc9b6b24877f59b222ade704bfaa42caa2a6
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/197e257da473c725dfe47759c3ee02f2398d8ea5
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/308c6d0e1f200fd26c71270c6e6bfcf0fc6ff082
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/6c32496964da0dc230cea763a0e934b2e02dabd5
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/d6a597450e686d4c6388bd3cdcb17224b4dae7f0
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/e2b2f0e2e34d71ae6c2a1114fd3c525930e84bc7
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/e7e3e90d671078455a3a08189f89d85b3da2de9e
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/eeaa345e128515135ccb864c04482180c08e3259
    Patch