UBUNTU-CVE-2026-68217: Medium severity ubuntu/linux vulnerability
In the Linux kernel, the following vulnerability has been resolved: media: pwc: Drain fillbuf on startstreaming() failure pwcisocinit() submits its isochronous URBs with usbsubmiturb(.., GFPKERNEL) in a loop. After the first URB is submitted, its completion handler pwcisochandler() can run on another CPU before the loop finishes: startstreaming() pwcisocinit() usbsubmiturb(urbs[0], GFPKERNEL) pwcisochandler(urbs[0]) pdev->fillbuf = pwcgetnextfillbuf(pdev) usbsubmiturb(urbs[i>0], ..) -> fails pwcisoccleanup(pdev) / kills URBs / return ret; pwccleanupqueuedbufs(pdev, VB2BUFSTATEQUEUED) pwcgetnextfillbuf() detaches a buffer from pdev->queuedbufs and stores it in pdev->fillbuf. The error path in startstreaming() only drains pdev->queuedbufs, so the buffer parked in pdev->fillbuf is leaked. vb2startstreaming() then triggers WARNON(ownedbydrvcount). stopstreaming() already handles this since commit 80b0963e1698 ("[media] pwc: fix WARNON"), which added the fillbuf drain in the teardown path but not in the startstreaming() error path. Mirror that handling on failure so startstreaming() returns with no buffer owned by the driver. Issue identified by automated review of the INV-003 series at https://sashiko.dev/
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-147.147+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79+fips1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-38.38 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 7.0.0-1016.16 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 7.0.0-1008.9 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Compensating control
On the start_streaming() failure path, drain pdev->fill_buf in addition to pdev->queued_bufs before returning, so no buffer remains owned by the driver.
Event History
Frequently Asked Questions
Which systems are exposed to this issue?
Systems using the affected Ubuntu kernel packages are exposed when the pwc media driver is used. The issue is in the driver's video-buffer handling during USB isochronous streaming startup.
What condition is required to trigger the problem?
An isochronous USB request must be submitted successfully, its completion handler must obtain a fill buffer, and submission of a later request must then fail while streaming is starting. This leaves a buffer parked in the driver's fill_buf field while the startup error path only drains the queued buffer list.
How could an administrator recognize that the issue has occurred?
The failure can result in a WARN_ON involving owned_by_drv_count when vb2_start_streaming() detects that a buffer is still owned by the driver after startup fails. The underlying symptom is a leaked video buffer in the pwc driver's fill_buf state.