unshare: don't drop active namespace references that were never taken
Active references on the namespaces of an nsproxy are taken when the
nsproxy is installed into a task in switch_task_namespaces() and
copy_namespaces() and dropped again by put_nsproxy() through
deactivate_nsproxy().
But ksys_unshare() calls put_nsproxy() on an nsproxy that was never
installed when set_cred_ucounts() fails. The new namespaces of that
nsproxy go from zero to minus one and the namespaces shared with the
caller lose a reference that belongs to the nsproxy the caller keeps
using:
WARNING: kernel/nscommon.c:171 at __ns_ref_active_put+0x1cd/0x230
nsproxy_ns_active_put
deactivate_nsproxy
ksys_unshare
Afterwards the namespaces the caller lives in aren't listed by listns()
anymore. set_cred_ucounts() only fails when alloc_ucounts() can't
allocate and it only allocates when the real uid of the caller differs
from its effective uid.
Commit cefd55bd2159 ("nsproxy: fix free_nsproxy() and simplify
create_new_namespaces()") separated the two cases on purpose.
nsproxy_free() frees an nsproxy that was prepared but never installed
and that's what a failed setns() uses in put_nsset(). Export it and use
it for a failed unshare() as well.
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Solution
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Workaround
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Fri, 23 Oct 2026 17:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-416 |
Fri, 23 Oct 2026 12:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: unshare: don't drop active namespace references that were never taken Active references on the namespaces of an nsproxy are taken when the nsproxy is installed into a task in switch_task_namespaces() and copy_namespaces() and dropped again by put_nsproxy() through deactivate_nsproxy(). But ksys_unshare() calls put_nsproxy() on an nsproxy that was never installed when set_cred_ucounts() fails. The new namespaces of that nsproxy go from zero to minus one and the namespaces shared with the caller lose a reference that belongs to the nsproxy the caller keeps using: WARNING: kernel/nscommon.c:171 at __ns_ref_active_put+0x1cd/0x230 nsproxy_ns_active_put deactivate_nsproxy ksys_unshare Afterwards the namespaces the caller lives in aren't listed by listns() anymore. set_cred_ucounts() only fails when alloc_ucounts() can't allocate and it only allocates when the real uid of the caller differs from its effective uid. Commit cefd55bd2159 ("nsproxy: fix free_nsproxy() and simplify create_new_namespaces()") separated the two cases on purpose. nsproxy_free() frees an nsproxy that was prepared but never installed and that's what a failed setns() uses in put_nsset(). Export it and use it for a failed unshare() as well. | |
| Title | unshare: don't drop active namespace references that were never taken | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-23T12:20:00.918Z
Reserved: 2026-09-25T10:25:14.384Z
Link: CVE-2026-98983
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-23T13:17:20.160
Modified: 2026-10-23T13:17:20.160
Link: CVE-2026-98983
Redhat
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OpenCVE Enrichment
Updated: 2026-10-23T17:00:15Z