CVE-2026-93781

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

scsi: core: Do not block on tag allocation in scsi_eh_lock_door()

scsi_eh_lock_door() is called from scsi_restart_operations() while the

host is still in the SHOST_RECOVERY state, i.e. before the host is

switched back to SHOST_RUNNING and scsi_run_host_queues() restarts the

queues. It allocates a request via scsi_alloc_request() with no flags,

so blk_mq_get_tag() may block waiting for a free sched tag when all tags

are already in use.

Those tags can be held by commands that were just requeued by

scsi_eh_flush_done_q() during error handling. Such commands cannot be

dispatched until the host leaves SHOST_RECOVERY and

scsi_run_host_queues() is called - which only happens *after*

scsi_eh_lock_door() returns.

This forms a circular dependency:

- scsi_eh_lock_door(), running in the SCSI error handler thread, waits

for a sched tag held by a requeued command;

- the requeued command cannot complete and release its sched tag until

the error handler thread leaves scsi_restart_operations() and restart

the queues.

For devices with a single driver tag (e.g. USB storage) it is a

guaranteed deadlock and I/O that can never be submitted. This problem

has also been reproduced in our environment.

Locking the door is a best-effort operation, and scsi_eh_lock_door()

already returns silently when the request allocation fails. Pass

BLK_MQ_REQ_NOWAIT to scsi_alloc_request() so the allocation fails

instead of blocking when no tag is available. This breaks the circular

dependency and allows the error handler to finish restarting the queues,

after which the pending commands are dispatched normally.