UBUNTU-CVE-2026-98314: Medium severity ubuntu/linux vulnerability
In the Linux kernel, the following vulnerability has been resolved: ALSA: pcm: set timer->privatedata before registering the PCM timer sndpcmtimerinit() calls snddeviceregister() to link the new struct sndtimer into the global timer list while it still carries hw.cresolution = sndpcmtimerresolution (and hw.start/hw.stop), and only afterwards sets timer->privatedata = substream. Once the timer is on the list under registermutex, a concurrent reader can already reach it through the same mutex and invoke these callbacks. /proc/asound/timers does this via cresolution(), and sndtimeropen()+sndtimerstart() reach start()/stop() the same way. All three dereference timer->privatedata, which for this brief window is NULL, giving a NULL-pointer dereference: substream = timer->privatedata; return substream->runtime ? ... // substream is NULL Move the privatedata/privatefree assignment before snddeviceregister() so the timer is never visible on the list without its privatedata set. On the snddeviceregister() failure path, privatefree() (sndpcmtimerfree()) can now run, but it only does substream->timer = NULL, which is already NULL at that point since substream->timer is set to the new timer just once, after a successful registration -- so the failure path stays safe.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1119.126~20.04.1 - Upgrade
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ubuntu/linux-azure-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1125.134~20.04.1 - Upgrade
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ubuntu/linux-azure-fde-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1124.133~20.04.1 - Upgrade
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ubuntu/linux-gcp-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1120.130~20.04.1 - Upgrade
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ubuntu/linux-hwe-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-202.212~20.04.1 - Upgrade
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ubuntu/linux-ibm-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1113.117~20.04.1 - Upgrade
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ubuntu/linux-intel-iotg-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1114.120~20.04.1 - Upgrade
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ubuntu/linux-lowlatency-hwe-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-197.207~20.04.1 - Upgrade
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ubuntu/linux-nvidia-tegra-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1070.72~20.04.1 - Upgrade
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ubuntu/linux-oracle-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1116.122~20.04.1 - Upgrade
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ubuntu/linux-riscv-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1113.117~20.04.2 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 5.15.0-202.212 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 5.15.0-1119.126 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 5.15.0-1125.134 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 5.15.0-1120.130 - Upgrade
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ubuntu/linux-lowlatencyto a version that resolves this vulnerability.Fixed in 5.15.0-197.207 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 5.15.0-1114.115 - Upgrade
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ubuntu/linux-bluefieldto a version that resolves this vulnerability.Fixed in 5.15.0-1103.105 - Upgrade
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ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 5.15.0-1119.126+fips1 - Upgrade
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ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-42.42~24.04.1 - Upgrade
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ubuntu/linux-riscv-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1~24.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-42.42 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1016.17 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1016.18 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1015.16 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1 - Compensating control
In snd_pcm_timer_init(), assign timer->private_data = substream before calling snd_device_register(), so the PCM timer cannot become visible on the global timer list before its private_data is initialized.
Event History
Frequently Asked Questions
What conditions are required to trigger the issue?
A concurrent reader must access a newly registered PCM timer during the brief interval before its private_data pointer is assigned. The described paths include reading /proc/asound/timers or opening and starting the timer through ALSA timer operations.
What is the practical impact of a successful trigger?
The affected callbacks dereference a NULL private_data pointer, causing a NULL-pointer dereference. The data describes this as a race during PCM timer initialization.