CVE-2025-71304: smack: /smack/doi: accept previously used values
In the Linux kernel, the following vulnerability has been resolved:
smack: /smack/doi: accept previously used values
Writing to /smack/doi a value that has ever been written there in the past disables networking for non-ambient labels. E.g.
# cat /smack/doi 3 # netlabelctl -p cipso list Configured CIPSO mappings (1) DOI value : 3 mapping type : PASSTHROUGH # netlabelctl -p map list Configured NetLabel domain mappings (3) domain: "" (IPv4) protocol: UNLABELED domain: DEFAULT (IPv4) protocol: CIPSO, DOI = 3 domain: DEFAULT (IPv6) protocol: UNLABELED
# cat /smack/ambient # cat /proc/$$/attr/smack/current # ping -c1 10.1.95.12 64 bytes from 10.1.95.12: icmpseq=1 ttl=64 time=0.964 ms # echo foo >/proc/$$/attr/smack/current # ping -c1 10.1.95.12 64 bytes from 10.1.95.12: icmpseq=1 ttl=64 time=0.956 ms unknown option 86
# echo 4 >/smack/doi # echo 3 >/smack/doi !> [ 214.050395] smkcipsodoi:691 cipso add rc = -17 # echo 3 >/smack/doi !> [ 249.402261] smkcipsodoi:678 remove rc = -2 !> [ 249.402261] smkcipsodoi:691 cipso add rc = -17
# ping -c1 10.1.95.12 !!> ping: 10.1.95.12: Address family for hostname not supported
# echo >/proc/$$/attr/smack/current # ping -c1 10.1.95.12 64 bytes from 10.1.95.12: icmpseq=1 ttl=64 time=0.617 ms
This happens because Smack keeps decommissioned DOIs, fails to re-add them, and consequently refuses to add the “default” domain map:
# netlabelctl -p cipso list Configured CIPSO mappings (2) DOI value : 3 mapping type : PASSTHROUGH DOI value : 4 mapping type : PASSTHROUGH # netlabelctl -p map list Configured NetLabel domain mappings (2) domain: "" (IPv4) protocol: UNLABELED !> (no ipv4 map for default domain here) domain: DEFAULT (IPv6) protocol: UNLABELED
Fix by clearing decommissioned DOI definitions and serializing concurrent DOI updates with a new lock.
Also: - allow /smack/doi to live unconfigured, since adding a map (netlblcfgcipsov4mapadd) may fail. CIPSOV4DOIUNKNOWN(0) indicates the unconfigured DOI - add new DOI before removing the old default map, so the old map remains if the add fails
(2008-02-04, Casey Schaufler)
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 6.8.0-134.134 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 6.8.0-1058.64 - Upgrade
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ubuntu/linux-gkeopto a version that resolves this vulnerability.Fixed in 6.8.0-1045.48 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 6.8.0-1060.61 - Upgrade
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ubuntu/linux-lowlatencyto a version that resolves this vulnerability.Fixed in 6.8.0-134.134.1 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 6.8.0-1058.61 - Upgrade
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ubuntu/linux-nvidia-lowlatencyto a version that resolves this vulnerability.Fixed in 6.8.0-1058.61.1 - Upgrade
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ubuntu/linux-nvidia-tegrato a version that resolves this vulnerability.Fixed in 6.8.0-1029.30 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1062.69+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1063.69+fips1 - Configuration
Allow /smack/doi to remain unconfigured by using CIPSO_V4_DOI_UNKNOWN(0) when no DOI is configured.
Smack /smack/doi = CIPSO_V4_DOI_UNKNOWN(0) - Operational
Clear decommissioned DOI definitions, serialize concurrent DOI updates with a lock, and add the new DOI before removing the old default map so the old map remains if adding the new map fails.
Event History
Frequently Asked Questions
Which systems and users are exposed?
Exposure is limited to Linux systems using Smack where a local user with low privileges can write to /smack/doi. The issue affects networking for non-ambient Smack labels; no user interaction is required.
What is the practical impact after exploitation?
Reusing a DOI value that was written previously can disable networking for processes running with non-ambient labels. The supplied example shows subsequent network attempts failing with an address-family error.
How can administrators identify a suspected occurrence?
Kernel messages may show CIPSO removal and addition failures, including "remove rc = -2" and "cipso add rc = -17", after writes to /smack/doi. Affected non-ambient-labeled processes may then be unable to communicate over the network while the ambient label remains able to do so.