Patchwork [Lucid,Oneiric,Precise,Quantal,Raring,CVE-2013-0914] signal: always clear sa_restorer on execve

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Submitter Luis Henriques
Date March 18, 2013, 4:30 p.m.
Message ID <1363624255-8181-1-git-send-email-luis.henriques@canonical.com>
Download mbox | patch
Permalink /patch/228684/
State New
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Luis Henriques - March 18, 2013, 4:30 p.m.
From: Kees Cook <keescook@chromium.org>

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>
---
 kernel/signal.c | 3 +++
 1 file changed, 3 insertions(+)
Tim Gardner - March 18, 2013, 4:42 p.m.

Patch

diff --git a/kernel/signal.c b/kernel/signal.c
index 3d09cf6..7591ccc 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -485,6 +485,9 @@  flush_signal_handlers(struct task_struct *t, int force_default)
 		if (force_default || ka->sa.sa_handler != SIG_IGN)
 			ka->sa.sa_handler = SIG_DFL;
 		ka->sa.sa_flags = 0;
+#ifdef SA_RESTORER
+		ka->sa.sa_restorer = NULL;
+#endif
 		sigemptyset(&ka->sa.sa_mask);
 		ka++;
 	}