signal: always clear sa_restorer on execve

CVE-2013-0914

BugLink: http://bugs.launchpad.net/bugs/1153813

When the new signal handlers are set up, the location of sa_restorer is
not cleared, leaking a parent process's address space location to
children.  This allows for a potential bypass of the parent's ASLR by
examining the sa_restorer value returned when calling sigaction().

Based on what should be considered "secret" about addresses, it only
matters across the exec not the fork (since the VMAs haven't changed
until the exec).  But since exec sets SIG_DFL and keeps sa_restorer,
this is where it should be fixed.

Given the few uses of sa_restorer, a "set" function was not written
since this would be the only use.  Instead, we use
__ARCH_HAS_SA_RESTORER, as already done in other places.

Example of the leak before applying this patch:

  $ cat /proc/$$/maps
  ...
  7fb9f3083000-7fb9f3238000 r-xp 00000000 fd:01 404469 .../libc-2.15.so
  ...
  $ ./leak
  ...
  7f278bc74000-7f278be29000 r-xp 00000000 fd:01 404469 .../libc-2.15.so
  ...
  1 0 (nil) 0x7fb9f30b94a0
  2 4000000 (nil) 0x7f278bcaa4a0
  3 4000000 (nil) 0x7f278bcaa4a0
  4 0 (nil) 0x7fb9f30b94a0
  ...

[akpm@linux-foundation.org: use SA_RESTORER for backportability]
Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Emese Revfy <re.emese@gmail.com>
Cc: Emese Revfy <re.emese@gmail.com>
Cc: PaX Team <pageexec@freemail.hu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Julien Tinnes <jln@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 2ca39528c01a933f6689cd6505ce65bd6d68a530)
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
UBUNTU: Ubuntu-3.0.0-32.51

Signed-off-by: Steve Conklin <sconklin@canonical.com>
UBUNTU: [Config] Created LTS backport branch

Oneiric initial backport.

Signed-off-by: Andy Whitcroft <apw@canonical.com>
UBUNTU: commonise the rebase scripting

Move to the new common rebase scripting framework.  This does not make
a new remote when pulling in the updates.  This avoids corrupting a
local remote if it already exists, limits the fetch only to the required
branch, and finally stops this repo being polluted by unnecessary tags.
Significantly improves rebase performance as a result.

Signed-off-by: Andy Whitcroft <apw@canonical.com>
UBUNTU: Ubuntu-lts-3.0-3.4

Signed-off-by: Andy Whitcroft <apw@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-4.5

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-5.6

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
UBUNTU: ensure we only build on the required architectures

Signed-off-by: Andy Whitcroft <apw@canonical.com>
UBUNTU: Get master branch udeb and firmware changes

 BugLink: http://bugs.launchpad.net/bugs/809584

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Revert "UBUNTU: ensure we only build on the required architectures"

This reverts commit 1b6a49e7668e0736d7feca92b0e1e360363da568.

Signed-off-by: Andy Whitcroft <apw@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-8.11

Signed-off-by: Andy Whitcroft <apw@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-11.18

Signed-off-by: Andy Whitcroft <apw@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-12.20

Signed-off-by: Andy Whitcroft <apw@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-13.21

Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-13.22

Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-14.23

Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-15.25

Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-15.26

Signed-off-by: Andy Whitcroft <apw@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-16.28

Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
UBUNTU: Ubuntu-lts-3.0.0-16.29

Signed-off-by: Brad Figg <brad.figg@canonical.com>