random: add and use memzero_explicit() for clearing data
authorDaniel Borkmann <dborkman@redhat.com>
Wed, 27 Aug 2014 03:16:35 +0000 (23:16 -0400)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Fri, 14 Nov 2014 16:47:55 +0000 (08:47 -0800)
commit25e1465ac3cfeafce34b3a47e773c4bc950054a3
tree31d1c7845bb872d25967f82d253b31b0561bdc1c
parent620c41147d873223d8aac0aa64793882b6217f09
random: add and use memzero_explicit() for clearing data

commit d4c5efdb97773f59a2b711754ca0953f24516739 upstream.

zatimend has reported that in his environment (3.16/gcc4.8.3/corei7)
memset() calls which clear out sensitive data in extract_{buf,entropy,
entropy_user}() in random driver are being optimized away by gcc.

Add a helper memzero_explicit() (similarly as explicit_bzero() variants)
that can be used in such cases where a variable with sensitive data is
being cleared out in the end. Other use cases might also be in crypto
code. [ I have put this into lib/string.c though, as it's always built-in
and doesn't need any dependencies then. ]

Fixes kernel bugzilla: 82041

Reported-by: zatimend@hotmail.co.uk
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/char/random.c
include/linux/string.h
lib/string.c