Xen bends own embargo rules to unbork risky Cirrus video emulation

It's 2017 and a VGA driver can take down a cloud. Seriously


The Xen Project has bent its own rules of vulnerability disclosure for a buggy and possibly exploitable video component that needs urgent attention.

It's not a hypervisor escape yet, but as the Xen advisory notes, it could be a pathway to one.

The crashable component is a VGA driver, of all things – the default Cirrus video emulator, which can be crashed by fiddling with display settings.

The bug is triggered by changing the display geometry, while simultaneously selecting a blank screen mode. The resize doesn't happen, but “will be properly handled during the next time a non-blank mode is selected during an update.”

So far so good. The problem is that other console components (the advisory picks out VNC emulation) see the resize and try to apply it. “When the display is resized to be larger than before, this can result in a heap overflow as console components will expect the display buffer to be larger than it is currently allocated.”

For Hardware Virtual Machine (HVM) guests, the process will crash through, but should only get the privileges of their guest kernel.

The Xen Project usually slaps a two-week embargo on bugs, so that clouds that use the hypervisor can sort things out before every hacker capable of spelling "HTML" descends on the millions of VMs they run.

However, what led to this one being shipped ahead of the normal embargo cycle is that the developers couldn't rule out a more serious exploit emerging.

“But the ability of a userspace process to trigger this vulnerability via legitimate commands to the kernel driver (thus elevating its privileges to that of the guest kernel) cannot be ruled out,” the advisory says. It also offers another reason for the early public disclosure, namely "to enable the community to have oversight of the Xen Project Security Team's decision-making."

The advisory includes patches. Users can also mitigate by running HVM with a stub domain; the advisory says it can also be mitigated by using the stgvga, but warns against this until the embargo period ends:

“It is NOT permitted during the embargo to switch from Cirrus VGA to Stdvga on public-facing systems with untrusted guest users or administrators. This is because it may give a clue where the issue lies. This mitigation is only permitted AFTER the embargo ends.” ®

Similar topics


Other stories you might like

  • DigitalOcean tries to take sting out of price hike with $4 VM
    Cloud biz says it is reacting to customer mix largely shifting from lone devs to SMBs

    DigitalOcean attempted to lessen the sting of higher prices this week by announcing a cut-rate instance aimed at developers and hobbyists.

    The $4-a-month droplet — what the infrastructure-as-a-service outfit calls its virtual machines — pairs a single virtual CPU with 512 MB of memory, 10 GB of SSD storage, and 500 GB a month in network bandwidth.

    The launch comes as DigitalOcean plans a sweeping price hike across much of its product portfolio, effective July 1. On the low-end, most instances will see pricing increase between $1 and $16 a month, but on the high-end, some products will see increases of as much as $120 in the case of DigitalOceans’ top-tier storage-optimized virtual machines.

    Continue reading
  • GPL legal battle: Vizio told by judge it will have to answer breach-of-contract claims
    Fine-print crucially deemed contractual agreement as well as copyright license in smartTV source-code case

    The Software Freedom Conservancy (SFC) has won a significant legal victory in its ongoing effort to force Vizio to publish the source code of its SmartCast TV software, which is said to contain GPLv2 and LGPLv2.1 copyleft-licensed components.

    SFC sued Vizio, claiming it was in breach of contract by failing to obey the terms of the GPLv2 and LGPLv2.1 licenses that require source code to be made public when certain conditions are met, and sought declaratory relief on behalf of Vizio TV owners. SFC wanted its breach-of-contract arguments to be heard by the Orange County Superior Court in California, though Vizio kicked the matter up to the district court level in central California where it hoped to avoid the contract issue and defend its corner using just federal copyright law.

    On Friday, Federal District Judge Josephine Staton sided with SFC and granted its motion to send its lawsuit back to superior court. To do so, Judge Staton had to decide whether or not the federal Copyright Act preempted the SFC's breach-of-contract allegations; in the end, she decided it didn't.

    Continue reading
  • US brings first-of-its-kind criminal charges of Bitcoin-based sanctions-busting
    Citizen allegedly moved $10m-plus in BTC into banned nation

    US prosecutors have accused an American citizen of illegally funneling more than $10 million in Bitcoin into an economically sanctioned country.

    It's said the resulting criminal charges of sanctions busting through the use of cryptocurrency are the first of their kind to be brought in the US.

    Under the United States' International Emergency Economic Powers Act (IEEA), it is illegal for a citizen or institution within the US to transfer funds, directly or indirectly, to a sanctioned country, such as Iran, Cuba, North Korea, or Russia. If there is evidence the IEEA was willfully violated, a criminal case should follow. If an individual or financial exchange was unwittingly involved in evading sanctions, they may be subject to civil action. 

    Continue reading
  • Meta hires network chip guru from Intel: What does this mean for future silicon?
    Why be a customer when you can develop your own custom semiconductors

    Analysis Here's something that should raise eyebrows in the datacenter world: Facebook parent company Meta has hired a veteran networking chip engineer from Intel to lead silicon design efforts in the internet giant's infrastructure hardware engineering group.

    Jon Dama started as director of silicon in May for Meta's infrastructure hardware group, a role that has him "responsible for several design teams innovating the datacenter for scale," according to his LinkedIn profile. In a blurb, Dama indicated that a team is already in place at Meta, and he hopes to "scale the next several doublings of data processing" with them.

    Though we couldn't confirm it, we think it's likely that Dama is reporting to Alexis Bjorlin, Meta's vice president of infrastructure hardware who previously worked with Dama when she was general manager of Intel's Connectivity group before serving a two-year stint at Broadcom.

    Continue reading
  • Lithium production needs investment to keep pace with battery demand
    Report says $42b will need to be poured into industry over next decade

    Growing demand for lithium for batteries means the sector will need $42 billion of investment to meet the anticipated level of orders by the end of the decade, according to a report.

    Lithium is used in batteries that power smartphones and laptops, but there is also rising use in electric vehicles which is putting additional pressure on supplies.

    The report, Benchmark Mineral Intelligence, predicts that demand will reach 2.4 million tons of lithium carbonate equivalent by 2030, roughly four times the 600,000 tons of lithium forecast to be produced this year.

    Continue reading

Biting the hand that feeds IT © 1998–2022