Subject: CVE-2024-46735: ublk_drv: fix NULL pointer dereference in ublk_ctrl_start_recovery()

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

ublk_drv: fix NULL pointer dereference in ublk_ctrl_start_recovery()

When two UBLK_CMD_START_USER_RECOVERY commands are submitted, the
first one sets 'ubq->ubq_daemon' to NULL, and the second one triggers
WARN in ublk_queue_reinit() and subsequently a NULL pointer dereference
issue.

Fix it by adding the check in ublk_ctrl_start_recovery() and return
immediately in case of zero 'ub->nr_queues_ready'.

  BUG: kernel NULL pointer dereference, address: 0000000000000028
  RIP: 0010:ublk_ctrl_start_recovery.constprop.0+0x82/0x180
  Call Trace:
   <TASK>
   ? __die+0x20/0x70
   ? page_fault_oops+0x75/0x170
   ? exc_page_fault+0x64/0x140
   ? asm_exc_page_fault+0x22/0x30
   ? ublk_ctrl_start_recovery.constprop.0+0x82/0x180
   ublk_ctrl_uring_cmd+0x4f7/0x6c0
   ? pick_next_task_idle+0x26/0x40
   io_uring_cmd+0x9a/0x1b0
   io_issue_sqe+0x193/0x3f0
   io_wq_submit_work+0x9b/0x390
   io_worker_handle_work+0x165/0x360
   io_wq_worker+0xcb/0x2f0
   ? finish_task_switch.isra.0+0x203/0x290
   ? finish_task_switch.isra.0+0x203/0x290
   ? __pfx_io_wq_worker+0x10/0x10
   ret_from_fork+0x2d/0x50
   ? __pfx_io_wq_worker+0x10/0x10
   ret_from_fork_asm+0x1a/0x30
   </TASK>

The Linux kernel CVE team has assigned CVE-2024-46735 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.1 with commit c732a852b419 and fixed in 6.1.110 with commit ca249435893d
	Issue introduced in 6.1 with commit c732a852b419 and fixed in 6.6.51 with commit 136a29d8112d
	Issue introduced in 6.1 with commit c732a852b419 and fixed in 6.10.10 with commit 7c890ef60bf4
	Issue introduced in 6.1 with commit c732a852b419 and fixed in 6.11 with commit e58f5142f883

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-46735
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/block/ublk_drv.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/ca249435893dda766f3845c15ca77ca5672022d8
	https://git.kernel.org/stable/c/136a29d8112df4ea0a57f9602ddf3579e04089dc
	https://git.kernel.org/stable/c/7c890ef60bf417d3fe5c6f7a9f6cef0e1d77f74f
	https://git.kernel.org/stable/c/e58f5142f88320a5b1449f96a146f2f24615c5c7