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CVE-2022-50335: 9p: set req refcount to zero to avoid uninitialized usage

In the Linux kernel, the following vulnerability has been resolved: 9p: set req refcount to zero to avoid uninitialized usage When a new request is allocated, the refcount will be zero if it is reused, but if the request is newly allocated from slab, it is not fully initialized before being added to idr. If the p9_read_work got a response before the refcount initiated. It will use a uninitialized req, which will result in a bad request data struct. Here is the logs from syzbot. Corrupted memory at 0xffff88807eade00b [ 0xff 0x07 0x00 0x00 0x00 0x00 0x00 0x00 . . . . . . . . ] (in kfence-#110): p9_fcall_fini net/9p/client.c:248 [inline] p9_req_put net/9p/client.c:396 [inline] p9_req_put+0x208/0x250 net/9p/client.c:390 p9_client_walk+0x247/0x540 net/9p/client.c:1165 clone_fid fs/9p/fid.h:21 [inline] v9fs_fid_xattr_set+0xe4/0x2b0 fs/9p/xattr.c:118 v9fs_xattr_set fs/9p/xattr.c:100 [inline] v9fs_xattr_handler_set+0x6f/0x120 fs/9p/xattr.c:159 __vfs_setxattr+0x119/0x180 fs/xattr.c:182 __vfs_setxattr_noperm+0x129/0x5f0 fs/xattr.c:216 __vfs_setxattr_locked+0x1d3/0x260 fs/xattr.c:277 vfs_setxattr+0x143/0x340 fs/xattr.c:309 setxattr+0x146/0x160 fs/xattr.c:617 path_setxattr+0x197/0x1c0 fs/xattr.c:636 __do_sys_setxattr fs/xattr.c:652 [inline] __se_sys_setxattr fs/xattr.c:648 [inline] __ia32_sys_setxattr+0xc0/0x160 fs/xattr.c:648 do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline] __do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178 do_fast_syscall_32+0x33/0x70 arch/x86/entry/common.c:203 entry_SYSENTER_compat_after_hwframe+0x70/0x82 Below is a similar scenario, the scenario in the syzbot log looks more complicated than this one, but this patch can fix it. T21124 p9_read_work ======================== second trans ================================= p9_client_walk p9_client_rpc p9_client_prepare_req p9_tag_alloc req = kmem_cache_alloc(p9_req_cache, GFP_NOFS); tag = idr_alloc << preempted >> req->tc.tag = tag; /* req->[refcount/tag] == uninitialized */ m->rreq = p9_tag_lookup(m->client, m->rc.tag); /* increments uninitalized refcount */ refcount_set(&req->refcount, 2); /* cb drops one ref */ p9_client_cb(req) /* reader thread drops its ref: request is incorrectly freed */ p9_req_put(req) /* use after free and ref underflow */ p9_req_put(req) To fix it, we can initialize the refcount to zero before add to idr.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2022-50335 is a Linux kernel 9p request-lifecycle bug. A race can expose an uninitialized request reference counter, leading to memory corruption and possible use-after-free behavior. The source bundle does not provide CVSS, confirmed impact beyond kernel memory safety, or active exploitation evidence.

Executive priority

Track and remediate through normal kernel patch governance unless your environment relies heavily on 9p or exposes it to untrusted workloads. Urgency increases for shared, virtualized, or multi-user systems, but the bundle does not justify an emergency exploitation-driven response.

Technical view

In Linux 9p, a request can be added to the IDR before its refcount is initialized. If p9_read_work receives a response during that window, it can look up the request and operate on an uninitialized refcount, corrupting request state and causing incorrect free, ref underflow, or use-after-free.

Likely exposure

Exposure is tied to Linux systems running affected kernel versions and using the 9p client/filesystem code path. The bundle lists Linux as affected but has ambiguous version notation, so teams should confirm status through their distribution kernel advisories and backport records.

Exploitation context

The provided sources include syzbot-derived crash evidence and a race scenario, but no public active exploitation claim. KEV status is false in the bundle. Treat this as a kernel memory-safety issue requiring patch tracking, not as confirmed exploited-in-the-wild activity.

Researcher notes

The key primitive is a race between request allocation/IDR publication and refcount initialization in net/9p/client.c. The described fix sets refcount to zero before IDR insertion. The source bundle lacks CVSS, CWE mapping, and downstream fixed-version detail.

Mitigation direction

  • Apply vendor or distribution kernel updates containing the referenced stable fixes.
  • Confirm whether your kernel includes the 9p refcount initialization patch.
  • Review Linux distribution advisories for backported fixed kernel versions.
  • Disable or avoid 9p usage where it is not operationally required.
  • Prioritize systems where untrusted users can influence 9p operations.

Validation and detection

  • Inventory Linux kernel versions across hosts and images.
  • Check whether 9p modules or filesystem usage are present.
  • Map deployed kernels against vendor fixed-version or backport advisories.
  • Verify the referenced stable commits exist in your kernel source package.
  • Review crash telemetry for 9p, refcount, or use-after-free indicators.
Prepared
Confidence
medium
Sources
6

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

Conservative CVE-to-ATT&CK context

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CVE-2022-50335 mapping review

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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
0Timeline events
0ADP providers
5Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux728356dedeff8ef999cb436c71333ef4ac51a81c, 728356dedeff8ef999cb436c71333ef4ac51a81c, 728356dedeff8ef999cb436c71333ef4ac51a81c, 728356dedeff8ef999cb436c71333ef4ac51a81c, 3665a4d9dca1bd06bc34afb72e637fe01b2776eeunaffected
LinuxLinux4.20, 0, 5.15.86, 6.0.16, 6.1.2, 6.2affected
Weakness

CWE details

No CWE listed

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