CVE-2021-47349: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47349 affects the Linux kernel's mwifiex driver, where a deadlock vulnerability was discovered when removing the driver (rmmod) or during firmware reset. The issue occurs because cfg80211_unregister_wdev() needs to bring down the link while holding the wiphy lock, which can lead to a deadlock condition. This vulnerability affects Linux kernel versions from 5.12 up to (excluding) 5.12.18 and from 5.13 up to (excluding) 5.13.3 (NVD).

The vulnerability stems from a locking issue in the mwifiex driver's interface deletion process. When unregistering the wireless device, the cfg80211_unregister_wdev() function needs to bring down the link, but this operation requires acquiring the same wiphy lock that's already held, resulting in a deadlock. The issue manifests when the netdev notifiers attempt to acquire the wiphy lock again during the device closure process. The CVSS v3.1 base score for this vulnerability is 5.5 (Medium), with the vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (NVD).

The primary impact of this vulnerability is a potential denial of service condition. When triggered, the system can become unresponsive for extended periods, as evidenced by the sample deadlock trace showing a task being blocked for more than 123 seconds. This affects system stability and availability, particularly during driver removal or firmware reset operations (Kernel Patch).

The vulnerability requires local access and can be triggered during specific operations such as removing the mwifiex driver (rmmod) or during firmware reset. While the attack complexity is low, it requires local privileged access to execute these operations (NVD).

The issue has been fixed in the Linux kernel through a patch that modifies the driver's behavior to bring down the network link before attempting to delete the interface. The fix ensures that the netdev is closed before acquiring the wiphy lock, preventing the deadlock condition. Users should upgrade to Linux kernel versions 5.12.18, 5.13.3 or later to receive the fix (Kernel Patch).