CVE-2021-47225

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

mac80211: fix deadlock in AP/VLAN handling

Syzbot reports that when you have AP_VLAN interfaces that are up and close the AP interface they belong to, we get a deadlock. No surprise - since we dev_close() them with the wiphy mutex held, which goes back into the netdev notifier in cfg80211 and tries to acquire the wiphy mutex there.

To fix this, we need to do two things:

1. prevent changing iftype while AP_VLANs are up, we cant easily fix this case since cfg80211 already calls us with the wiphy mutex held, but change_interface() is relatively rare in drivers anyway, so changing iftype isnt used much (and userspace has to fall back to down/change/up anyway)
2. pull the dev_close() loop over VLANs out of the wiphy mutex section in the normal stop case

Weakness

The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.

Affected Software

Extended Description

Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/25.html
• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/27.html

References

• https://git.kernel.org/stable/c/8043903fcb72f545c52e3ec74d6fd82ef79ce7c5
• https://git.kernel.org/stable/c/d5befb224edbe53056c2c18999d630dafb4a08b9
• https://git.kernel.org/stable/c/8043903fcb72f545c52e3ec74d6fd82ef79ce7c5
• https://git.kernel.org/stable/c/d5befb224edbe53056c2c18999d630dafb4a08b9