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Heiko Carstens d0290bc20d fs/proc/kcore.c: use probe_kernel_read() instead of memcpy() 
Commit df04abfd18 ("fs/proc/kcore.c: Add bounce buffer for ktext
data") added a bounce buffer to avoid hardened usercopy checks.  Copying
to the bounce buffer was implemented with a simple memcpy() assuming
that it is always valid to read from kernel memory iff the
kern_addr_valid() check passed.

A simple, but pointless, test case like "dd if=/proc/kcore of=/dev/null"
now can easily crash the kernel, since the former execption handling on
invalid kernel addresses now doesn't work anymore.

Also adding a kern_addr_valid() implementation wouldn't help here.  Most
architectures simply return 1 here, while a couple implemented a page
table walk to figure out if something is mapped at the address in
question.

With DEBUG_PAGEALLOC active mappings are established and removed all the
time, so that relying on the result of kern_addr_valid() before
executing the memcpy() also doesn't work.

Therefore simply use probe_kernel_read() to copy to the bounce buffer.
This also allows to simplify read_kcore().

At least on s390 this fixes the observed crashes and doesn't introduce
warnings that were removed with df04abfd18 ("fs/proc/kcore.c: Add
bounce buffer for ktext data"), even though the generic
probe_kernel_read() implementation uses uaccess functions.

While looking into this I'm also wondering if kern_addr_valid() could be
completely removed...(?)

Link: http://lkml.kernel.org/r/20171202132739.99971-1-heiko.carstens@de.ibm.com
Fixes: df04abfd18 ("fs/proc/kcore.c: Add bounce buffer for ktext data")
Fixes: f5509cc18d ("mm: Hardened usercopy")
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2018-02-06 18:32:43 -08:00
Documentation Merge branch 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs 2018-02-05 13:05:20 -08:00
LICENSES
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arch kasan: clean up KASAN_SHADOW_SCALE_SHIFT usage 2018-02-06 18:32:43 -08:00
block for-linus-20180204 2018-02-04 11:16:35 -08:00
certs
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crypto
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drivers remoteproc updates for v4.16 2018-02-05 10:07:40 -08:00
firmware
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fs fs/proc/kcore.c: use probe_kernel_read() instead of memcpy() 2018-02-06 18:32:43 -08:00
include kasan: clean up KASAN_SHADOW_SCALE_SHIFT usage 2018-02-06 18:32:43 -08:00
init
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ipc
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kernel Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-02-04 11:43:30 -08:00
lib kasan: remove redundant initialization of variable 'real_size' 2018-02-06 18:32:43 -08:00
mm kasan: fix prototype author email address 2018-02-06 18:32:43 -08:00
net Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-02-04 11:45:55 -08:00
samples
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scripts kasan: support alloca() poisoning 2018-02-06 18:32:42 -08:00
security Currently, hardened usercopy performs dynamic bounds checking on slab 2018-02-03 16:25:42 -08:00
sound
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tools Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-02-04 11:45:55 -08:00
usr
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virt Currently, hardened usercopy performs dynamic bounds checking on slab 2018-02-03 16:25:42 -08:00
.cocciconfig
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.get_maintainer.ignore
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.gitattributes
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.gitignore
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.mailmap
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COPYING
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CREDITS
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Kbuild
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Kconfig
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MAINTAINERS Bug fixes galore, removal of the ntb atom driver, and updates to the ntb 2018-02-04 11:13:49 -08:00
Makefile kasan: don't emit builtin calls when sanitization is off 2018-02-06 18:32:42 -08:00
README
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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.