CVE-2021-47111

In the Linux kernel, the following vulnerability has been resolved:

xen-netback: take a reference to the RX task thread

Do this in order to prevent the task from being freed if the thread returns (which can be triggered by the frontend) before the call to kthread_stop done as part of the backend tear down. Not taking the reference will lead to a use-after-free in that scenario. Such reference was taken before but dropped as part of the rework done in 2ac061ce97f4.

Reintroduce the reference taking and add a comment this time explaining why its needed.

This is XSA-374 / CVE-2021-28691.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/107866a8eb0b664675a260f1ba0655010fac1e08
• https://git.kernel.org/stable/c/6b53db8c4c14b4e7256f058d202908b54a7b85b4
• https://git.kernel.org/stable/c/caec9bcaeb1a5f03f2d406305355c853af10c13e
• https://git.kernel.org/stable/c/107866a8eb0b664675a260f1ba0655010fac1e08
• https://git.kernel.org/stable/c/6b53db8c4c14b4e7256f058d202908b54a7b85b4
• https://git.kernel.org/stable/c/caec9bcaeb1a5f03f2d406305355c853af10c13e