Subject: CVE-2021-47375: blktrace: Fix uaf in blk_trace access after removing by sysfs

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

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

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

blktrace: Fix uaf in blk_trace access after removing by sysfs

There is an use-after-free problem triggered by following process:

      P1(sda)				P2(sdb)
			echo 0 > /sys/block/sdb/trace/enable
			  blk_trace_remove_queue
			    synchronize_rcu
			    blk_trace_free
			      relay_close
rcu_read_lock
__blk_add_trace
  trace_note_tsk
  (Iterate running_trace_list)
			        relay_close_buf
				  relay_destroy_buf
				    kfree(buf)
    trace_note(sdb's bt)
      relay_reserve
        buf->offset <- nullptr deference (use-after-free) !!!
rcu_read_unlock

[  502.714379] BUG: kernel NULL pointer dereference, address:
0000000000000010
[  502.715260] #PF: supervisor read access in kernel mode
[  502.715903] #PF: error_code(0x0000) - not-present page
[  502.716546] PGD 103984067 P4D 103984067 PUD 17592b067 PMD 0
[  502.717252] Oops: 0000 [#1] SMP
[  502.720308] RIP: 0010:trace_note.isra.0+0x86/0x360
[  502.732872] Call Trace:
[  502.733193]  __blk_add_trace.cold+0x137/0x1a3
[  502.733734]  blk_add_trace_rq+0x7b/0xd0
[  502.734207]  blk_add_trace_rq_issue+0x54/0xa0
[  502.734755]  blk_mq_start_request+0xde/0x1b0
[  502.735287]  scsi_queue_rq+0x528/0x1140
...
[  502.742704]  sg_new_write.isra.0+0x16e/0x3e0
[  502.747501]  sg_ioctl+0x466/0x1100

Reproduce method:
  ioctl(/dev/sda, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])
  ioctl(/dev/sda, BLKTRACESTART)
  ioctl(/dev/sdb, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])
  ioctl(/dev/sdb, BLKTRACESTART)

  echo 0 > /sys/block/sdb/trace/enable &
  // Add delay(mdelay/msleep) before kernel enters blk_trace_free()

  ioctl$SG_IO(/dev/sda, SG_IO, ...)
  // Enters trace_note_tsk() after blk_trace_free() returned
  // Use mdelay in rcu region rather than msleep(which may schedule out)

Remove blk_trace from running_list before calling blk_trace_free() by
sysfs if blk_trace is at Blktrace_running state.

The Linux kernel CVE team has assigned CVE-2021-47375 to this issue.

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

	Issue introduced in 2.6.30 with commit c71a89615411 and fixed in 4.4.286 with commit 488da313edf3
	Issue introduced in 2.6.30 with commit c71a89615411 and fixed in 4.9.285 with commit dacfd5e4d114
	Issue introduced in 2.6.30 with commit c71a89615411 and fixed in 4.14.249 with commit d56171d9360c
	Issue introduced in 2.6.30 with commit c71a89615411 and fixed in 4.19.209 with commit 677e362ba807
	Issue introduced in 2.6.30 with commit c71a89615411 and fixed in 5.4.150 with commit ebb8d26d93c3
	Issue introduced in 2.6.30 with commit c71a89615411 and fixed in 5.10.70 with commit 3815fe7371d2
	Issue introduced in 2.6.30 with commit c71a89615411 and fixed in 5.14.9 with commit a5f8e8619261
	Issue introduced in 2.6.30 with commit c71a89615411 and fixed in 5.15 with commit 5afedf670caf

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-2021-47375
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:
	kernel/trace/blktrace.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/488da313edf3abea7f7733efe011c96b23740ab5
	https://git.kernel.org/stable/c/dacfd5e4d1142bfb3809aab3634a375f6f373269
	https://git.kernel.org/stable/c/d56171d9360c0170c5c5f8f7e2362a2e999eca40
	https://git.kernel.org/stable/c/677e362ba807f3aafe6f405c07e0b37244da5222
	https://git.kernel.org/stable/c/ebb8d26d93c3ec3c7576c52a8373a2309423c069
	https://git.kernel.org/stable/c/3815fe7371d2411ce164281cef40d9fc7b323dee
	https://git.kernel.org/stable/c/a5f8e86192612d0183047448d8bbe7918b3f1a26
	https://git.kernel.org/stable/c/5afedf670caf30a2b5a52da96eb7eac7dee6a9c9