CVE-2021-47505

Technical Description

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

aio: fix use-after-free due to missing POLLFREE handling

signalfd_poll() and binder_poll() are special in that they use a

waitqueue whose lifetime is the current task, rather than the struct

file as is normally the case. This is okay for blocking polls, since a

blocking poll occurs within one task; however, non-blocking polls

require another solution. This solution is for the queue to be cleared

before it is freed, by sending a POLLFREE notification to all waiters.

Unfortunately, only eventpoll handles POLLFREE. A second type of

non-blocking poll, aio poll, was added in kernel v4.18, and it doesn't

handle POLLFREE. This allows a use-after-free to occur if a signalfd or

binder fd is polled with aio poll, and the waitqueue gets freed.

Fix this by making aio poll handle POLLFREE.

A patch by Ramji Jiyani <[email protected]>

(https://lore.kernel.org/r/[email protected])

tried to do th

Remediation

Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected Products

References