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Linux kernel modifications for the Kernel Hacking exam
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Martin K. Petersen c92a6b5d63 scsi: core: Query VPD size before getting full page 
We currently default to 255 bytes when fetching VPD pages during discovery.
However, we have had a few devices that are known to wedge if the requested
buffer exceeds a certain size. See commit af73623f5f ("[SCSI] sd: Reduce
buffer size for vpd request") which works around one example of this
problem in the SCSI disk driver.

With commit d188b0675b ("scsi: core: Add sysfs attributes for VPD pages
0h and 89h") we now risk triggering the same issue in the generic midlayer
code.

The problem with the ATA VPD page in particular is that the SCSI portion of
the page is trailed by 512 bytes of verbatim ATA Identify Device
information.  However, not all controllers actually provide the additional
512 bytes and will lock up if one asks for more than the 64 bytes
containing the SCSI protocol fields.

Instead of picking a new, somewhat arbitrary, number of bytes for the VPD
buffer size, start fetching the 4-byte header for each page. The header
contains the size of the page as far as the device is concerned. We can use
the reported size to specify the correct allocation length when
subsequently fetching the full page.

The header validation is done by a new helper function scsi_get_vpd_size()
and both scsi_get_vpd_page() and scsi_get_vpd_buf() now rely on this to
query the page size.

In addition, scsi_get_vpd_page() is simplified to mirror the logic in
scsi_get_vpd_page(). This involves removing the Supported VPD Pages lookup
prior to attempting to query a page. There does not appear any evidence,
even in the oldest SCSI specs, that this step is required. We already rely
on scsi_get_vpd_page() throughout the stack and this function never
consulted the Supported VPD Pages. Since this has not caused any problems
it should be safe to remove the precondition from scsi_get_vpd_page().

Instrumented runs also revealed that the Supported VPD Pages lookup had
little effect since the device page index often was larger than the
supplied buffer size. As a result, inquiries frequently bypassed the index
check and went through the "If we ran off the end of the buffer, give us
the benefit of the doubt" code path which assumed the page was present
despite not being listed. The revised code takes both the page size
reported by the device as well as the size of the buffer provided by the
scsi_get_vpd_page() caller into account.

Link: https://lore.kernel.org/r/20220302053559.32147-3-martin.petersen@oracle.com
Fixes: d188b0675b ("scsi: core: Add sysfs attributes for VPD pages 0h and 89h")
Reported-by: Maciej W. Rozycki <macro@orcam.me.uk>
Tested-by: Maciej W. Rozycki <macro@orcam.me.uk>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
2022-05-02 16:59:10 -04:00
arch A set of x86 fixes and updates: 2022-04-03 12:15:47 -07:00
block for-5.18/block-2022-04-01 2022-04-01 16:20:00 -07:00
certs Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
crypto for-5.18/64bit-pi-2022-03-25 2022-03-26 12:01:35 -07:00
Documentation Updates to Tracing: 2022-04-03 12:26:01 -07:00
drivers scsi: core: Query VPD size before getting full page 2022-05-02 16:59:10 -04:00
fs Updates to Tracing: 2022-04-03 12:26:01 -07:00
include scsi: core: Query VPD size before getting full page 2022-05-02 16:59:10 -04:00
init Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
ipc fs: allocate inode by using alloc_inode_sb() 2022-03-22 15:57:03 -07:00
kernel Updates to Tracing: 2022-04-03 12:26:01 -07:00
lib for-5.18/block-2022-04-01 2022-04-01 16:20:00 -07:00
LICENSES
mm Filesystem/VFS changes for 5.18, part two 2022-04-01 13:50:50 -07:00
net Networking fixes for 5.18-rc1 and rethook patches. 2022-03-31 11:23:31 -07:00
samples dma-mapping updates for Linux 5.18 2022-03-29 08:50:14 -07:00
scripts modpost: restore the warning message for missing symbol versions 2022-04-03 03:11:51 +09:00
security hardening updates for v5.18-rc1-fix1 2022-03-31 11:43:01 -07:00
sound sound fixes for 5.18-rc1 2022-04-01 10:32:46 -07:00
tools A set of x86 fixes and updates: 2022-04-03 12:15:47 -07:00
usr Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
virt KVM: Remove dirty handling from gfn_to_pfn_cache completely 2022-04-02 05:34:41 -04:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap mailmap: update Kirill's email 2022-04-01 11:46:09 -07:00
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS scsi: iscsi: MAINTAINERS: Add Mike Christie as co-maintainer 2022-04-11 22:09:35 -04:00
Makefile Linux 5.18-rc1 2022-04-03 14:08:21 -07:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.