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Kees Cook e52432e164 tpm: vtpm_proxy: Check length to avoid compiler warning
When building with -Warray-bounds under GCC 11.2, this warning was
emitted:

In function 'memset',
    inlined from 'vtpm_proxy_fops_read' at drivers/char/tpm/tpm_vtpm_proxy.c:102:2:
./include/linux/fortify-string.h:43:33: warning: '__builtin_memset' pointer overflow between offset 164 and size [2147483648, 4294967295]
[-Warray-bounds]
   43 | #define __underlying_memset     __builtin_memset
      |                                 ^

This warning appears to be triggered due to the "count < len"
check in vtpm_proxy_fops_read() splitting the CFG[1], and the compiler
attempting to reason about the possible value range in len compared
to the buffer size.

In order to silence this warning, and to keep this code robust if the
use of proxy_dev->req_len ever changes in the future, explicitly check
the size of len before reaching the memset().

[1] https://lore.kernel.org/lkml/CAG48ez1iTF9KegKJrW5a3WzXgCPZJ73nS2_e5esKJRppdzvv8g@mail.gmail.com

Cc: Peter Huewe <peterhuewe@gmx.de>
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: linux-integrity@vger.kernel.org
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Link: https://lore.kernel.org/lkml/4b59d305-6858-1514-751a-37853ad777be@linux.ibm.com
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220119184354.3367603-1-keescook@chromium.org
History 2022-02-27 10:58:04 -08:00
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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.