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Linus Torvalds 16d7ceb04b mmap: introduce sane default mmap limits 
commit be83bbf806 upstream.

The internal VM "mmap()" interfaces are based on the mmap target doing
everything using page indexes rather than byte offsets, because
traditionally (ie 32-bit) we had the situation that the byte offset
didn't fit in a register.  So while the mmap virtual address was limited
by the word size of the architecture, the backing store was not.

So we're basically passing "pgoff" around as a page index, in order to
be able to describe backing store locations that are much bigger than
the word size (think files larger than 4GB etc).

But while this all makes a ton of sense conceptually, we've been dogged
by various drivers that don't really understand this, and internally
work with byte offsets, and then try to work with the page index by
turning it into a byte offset with "pgoff << PAGE_SHIFT".

Which obviously can overflow.

Adding the size of the mapping to it to get the byte offset of the end
of the backing store just exacerbates the problem, and if you then use
this overflow-prone value to check various limits of your device driver
mmap capability, you're just setting yourself up for problems.

The correct thing for drivers to do is to do their limit math in page
indices, the way the interface is designed.  Because the generic mmap
code _does_ test that the index doesn't overflow, since that's what the
mmap code really cares about.

HOWEVER.

Finding and fixing various random drivers is a sisyphean task, so let's
just see if we can just make the core mmap() code do the limiting for
us.  Realistically, the only "big" backing stores we need to care about
are regular files and block devices, both of which are known to do this
properly, and which have nice well-defined limits for how much data they
can access.

So let's special-case just those two known cases, and then limit other
random mmap users to a backing store that still fits in "unsigned long".
Realistically, that's not much of a limit at all on 64-bit, and on
32-bit architectures the only worry might be the GPU drivers, which can
have big physical address spaces.

To make it possible for drivers like that to say that they are 64-bit
clean, this patch does repurpose the "FMODE_UNSIGNED_OFFSET" bit in the
file flags to allow drivers to mark their file descriptors as safe in
the full 64-bit mmap address space.

[ The timing for doing this is less than optimal, and this should really
  go in a merge window. But realistically, this needs wide testing more
  than it needs anything else, and being main-line is the only way to do
  that.

  So the earlier the better, even if it's outside the proper development
  cycle        - Linus ]

Cc: Kees Cook <keescook@chromium.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Dave Airlie <airlied@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2018-06-11 22:49:18 +02:00
Documentation pinctrl: artpec6: dt: add missing pin group uart5nocts 2018-05-30 07:52:37 +02:00
arch powerpc/mm/slice: Fix hugepage allocation at hint address on 8xx 2018-06-05 11:42:00 +02:00
block block: display the correct diskname for bio 2018-05-30 07:52:09 +02:00
certs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
crypto PKCS#7: fix direct verification of SignerInfo signature 2018-05-30 07:52:01 +02:00
drivers scsi: sd_zbc: Avoid that resetting a zone fails sporadically 2018-06-11 22:49:17 +02:00
firmware License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fs xfs: detect agfl count corruption and reset agfl 2018-06-05 11:41:55 +02:00
include iio:buffer: make length types match kfifo types 2018-06-05 11:41:58 +02:00
init kmemcheck: stop using GFP_NOTRACK and SLAB_NOTRACK 2018-02-22 15:42:23 +01:00
ipc ipc/shm: fix shmat() nil address after round-down when remapping 2018-05-30 07:51:49 +02:00
kernel tracing: Make the snapshot trigger work with instances 2018-06-05 11:41:56 +02:00
lib lib/test_kmod.c: fix limit check on number of test devices created 2018-05-30 07:52:14 +02:00
mm mmap: introduce sane default mmap limits 2018-06-11 22:49:18 +02:00
net tcp: avoid integer overflows in tcp_rcv_space_adjust() 2018-06-05 11:41:58 +02:00
samples samples/bpf: Partially fixes the bpf.o build 2018-04-26 11:02:12 +02:00
scripts builddeb: Fix header package regarding dtc source links 2018-05-30 07:52:21 +02:00
security selinux: KASAN: slab-out-of-bounds in xattr_getsecurity 2018-06-05 11:41:56 +02:00
sound ASoC: Intel: sst: remove redundant variable dma_dev_name 2018-06-05 11:41:57 +02:00
tools objtool: Fix "noreturn" detection for recursive sibling calls 2018-06-05 11:41:55 +02:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt KVM: arm/arm64: vgic: Add missing irq_lock to vgic_mmio_read_pending 2018-05-30 07:52:15 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING
…
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS dt-bindings: Document mti,mips-cpc binding 2018-03-15 10:54:35 +01:00
Makefile Linux 4.14.48 2018-06-05 11:42:00 +02:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

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

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

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.