In the Linux kernel, the following vulnerability has been resolved: 9p: avoid putting oldfid in p9_client_walk() error path When p9_client_walk() is… (CVE-2026-63795)
In the Linux kernel, the following vulnerability has been resolved: 9p: avoid putting oldfid in p9_client_walk() error path When p9_client_walk() is called with clone set to false, fid aliases oldfid. If the walk subsequently fails after the request has been sent, the error path jumps to clunk_fid, which currently calls p9_fid_put(fid) unconditionally. This drops a reference to oldfid even though ownership of oldfid remains with the caller. If this is the last reference, oldfid can be clunked and destroyed while the caller still expects it to be valid. A later use or put of oldfid can then trigger a use-after-free or refcount underflow. Fix this by only putting fid in the clunk_fid error path when it does not alias oldfid, matching the existing guard in the error path below. This can be triggered when a multi-component walk is split into multiple p9_client_walk() calls and a later non-cloning walk fails. A reproducer and refcount warning logs are available on request.
AI Analysis
Technical Summary
The vulnerability in the Linux kernel's 9p client implementation involves improper reference counting in the p9_client_walk() function. When clone is false, fid aliases oldfid, but if a walk fails after the request is sent, the error path unconditionally calls p9_fid_put(fid), dropping a reference to oldfid incorrectly. If this was the last reference, oldfid is destroyed prematurely, leading to use-after-free or refcount underflow conditions. The fix ensures fid is only put in the error path when it does not alias oldfid, preventing premature destruction.
Potential Impact
This vulnerability can cause use-after-free or reference count underflow in the Linux kernel's 9p client code, potentially leading to memory corruption or kernel instability. There is no indication of known exploits in the wild.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance.
In the Linux kernel, the following vulnerability has been resolved: 9p: avoid putting oldfid in p9_client_walk() error path When p9_client_walk() is… (CVE-2026-63795)
Description
In the Linux kernel, the following vulnerability has been resolved: 9p: avoid putting oldfid in p9_client_walk() error path When p9_client_walk() is called with clone set to false, fid aliases oldfid. If the walk subsequently fails after the request has been sent, the error path jumps to clunk_fid, which currently calls p9_fid_put(fid) unconditionally. This drops a reference to oldfid even though ownership of oldfid remains with the caller. If this is the last reference, oldfid can be clunked and destroyed while the caller still expects it to be valid. A later use or put of oldfid can then trigger a use-after-free or refcount underflow. Fix this by only putting fid in the clunk_fid error path when it does not alias oldfid, matching the existing guard in the error path below. This can be triggered when a multi-component walk is split into multiple p9_client_walk() calls and a later non-cloning walk fails. A reproducer and refcount warning logs are available on request.
CVSS v3.1
Score 10.0critical
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in the Linux kernel's 9p client implementation involves improper reference counting in the p9_client_walk() function. When clone is false, fid aliases oldfid, but if a walk fails after the request is sent, the error path unconditionally calls p9_fid_put(fid), dropping a reference to oldfid incorrectly. If this was the last reference, oldfid is destroyed prematurely, leading to use-after-free or refcount underflow conditions. The fix ensures fid is only put in the error path when it does not alias oldfid, preventing premature destruction.
Potential Impact
This vulnerability can cause use-after-free or reference count underflow in the Linux kernel's 9p client code, potentially leading to memory corruption or kernel instability. There is no indication of known exploits in the wild.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-jj7f-gfpp-fxfg
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-63795"]
- Ecosystems
- []
- Database Specific Severity
- null
- Cvss Version
- 3.1
Threat ID: 6a5d27ad2a4a8d59891318e1
Added to database: 07/19/2026, 19:38:21 UTC
Last enriched: 07/19/2026, 20:20:34 UTC
Last updated: 09/01/2026, 10:52:10 UTC
Views: 79
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