CVE-2021-47192

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

scsi: core: sysfs: Fix hang when device state is set via sysfs

This fixes a regression added with:

commit f0f82e2476f6 (scsi: core: Fix capacity set to zero after offlinining device)

The problem is that after iSCSI recovery, iscsid will call into the kernel to set the devs state to running, and with that patch we now call scsi_rescan_device() with the state_mutex held. If the SCSI error handler thread is just starting to test the device in scsi_send_eh_cmnd() then its going to try to grab the state_mutex.

We are then stuck, because when scsi_rescan_device() tries to send its I/O scsi_queue_rq() calls -> scsi_host_queue_ready() -> scsi_host_in_recovery() which will return true (the host state is still in recovery) and I/O will just be requeued. scsi_send_eh_cmnd() will then never be able to grab the state_mutex to finish error handling.

To prevent the deadlock move the rescan-related code to after we drop the state_mutex.

This also adds a check for if we are already in the running state. This prevents extra scans and helps the iscsid case where if the transport class has already onlined the device during its recovery process then we dont need userspace to do it again plus possibly block that daemon.

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/4edd8cd4e86dd3047e5294bbefcc0a08f66a430f
• https://git.kernel.org/stable/c/a792e0128d232251edb5fdf42fb0f9fbb0b44a73
• https://git.kernel.org/stable/c/bcc0e3175a976b7fa9a353960808adb0bb49ead8
• https://git.kernel.org/stable/c/edd783162bf2385b43de6764f2d4c6e9f4f6be27
• https://git.kernel.org/stable/c/4edd8cd4e86dd3047e5294bbefcc0a08f66a430f
• https://git.kernel.org/stable/c/a792e0128d232251edb5fdf42fb0f9fbb0b44a73
• https://git.kernel.org/stable/c/bcc0e3175a976b7fa9a353960808adb0bb49ead8
• https://git.kernel.org/stable/c/edd783162bf2385b43de6764f2d4c6e9f4f6be27