Subject: CVE-2021-47182: scsi: core: Fix scsi_mode_sense() buffer length handling

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

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

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

scsi: core: Fix scsi_mode_sense() buffer length handling

Several problems exist with scsi_mode_sense() buffer length handling:

 1) The allocation length field of the MODE SENSE(10) command is 16-bits,
    occupying bytes 7 and 8 of the CDB. With this command, access to mode
    pages larger than 255 bytes is thus possible. However, the CDB
    allocation length field is set by assigning len to byte 8 only, thus
    truncating buffer length larger than 255.

 2) If scsi_mode_sense() is called with len smaller than 8 with
    sdev->use_10_for_ms set, or smaller than 4 otherwise, the buffer length
    is increased to 8 and 4 respectively, and the buffer is zero filled
    with these increased values, thus corrupting the memory following the
    buffer.

Fix these 2 problems by using put_unaligned_be16() to set the allocation
length field of MODE SENSE(10) CDB and by returning an error when len is
too small.

Furthermore, if len is larger than 255B, always try MODE SENSE(10) first,
even if the device driver did not set sdev->use_10_for_ms. In case of
invalid opcode error for MODE SENSE(10), access to mode pages larger than
255 bytes are not retried using MODE SENSE(6). To avoid buffer length
overflows for the MODE_SENSE(10) case, check that len is smaller than 65535
bytes.

While at it, also fix the folowing:

 * Use get_unaligned_be16() to retrieve the mode data length and block
   descriptor length fields of the mode sense reply header instead of using
   an open coded calculation.

 * Fix the kdoc dbd argument explanation: the DBD bit stands for Disable
   Block Descriptor, which is the opposite of what the dbd argument
   description was.

The Linux kernel CVE team has assigned CVE-2021-47182 to this issue.

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

	Fixed in 5.15.5 with commit e15de347faf4
	Fixed in 5.16 with commit 17b49bcbf835

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-2021-47182
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/scsi/scsi_lib.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/e15de347faf4a9f494cbd4e9a623d343dc1b5851
	https://git.kernel.org/stable/c/17b49bcbf8351d3dbe57204468ac34f033ed60bc