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Mon, 11 Mar 2013 13:13:43 -0700
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Date: Mon, 11 Mar 2013 13:13:42 -0700
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From: Kees Cook <keescook@chromium.org>
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To: linux-kernel@vger.kernel.org
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Cc: Al Viro <viro@zeniv.linux.org.uk>, Oleg Nesterov <oleg@redhat.com>,
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Andrew Morton <akpm@linux-foundation.org>,
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"Eric W. Biederman" <ebiederm@xmission.com>,
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Serge Hallyn <serge.hallyn@canonical.com>,
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Emese Revfy <re.emese@gmail.com>,
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PaX Team <pageexec@freemail.hu>, jln@google.com
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Subject: [PATCH v2] signal: always clear sa_restorer on execve
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Message-ID: <20130311201342.GA19824@www.outflux.net>
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When the new signal handlers are set up, the location of sa_restorer
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is not cleared, leaking a parent process's address space location to
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children. This allows for a potential bypass of the parent's ASLR by
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examining the sa_restorer value returned when calling sigaction().
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Based on what should be considered "secret" about addresses, it only
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matters across the exec not the fork (since the VMAs haven't changed
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until the exec). But since exec sets SIG_DFL and keeps sa_restorer,
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this is where it should be fixed.
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Given the few uses of sa_restorer, a "set" function was not written
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since this would be the only use. Instead, we use __ARCH_HAS_SA_RESTORER,
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as already done in other places.
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Example of the leak before applying this patch:
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$ cat /proc/$$/maps
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...
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7fb9f3083000-7fb9f3238000 r-xp 00000000 fd:01 404469 .../libc-2.15.so
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...
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$ ./leak
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...
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7f278bc74000-7f278be29000 r-xp 00000000 fd:01 404469 .../libc-2.15.so
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...
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1 0 (nil) 0x7fb9f30b94a0
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2 4000000 (nil) 0x7f278bcaa4a0
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3 4000000 (nil) 0x7f278bcaa4a0
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4 0 (nil) 0x7fb9f30b94a0
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...
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Signed-off-by: Kees Cook <keescook@chromium.org>
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Reported-by: Emese Revfy <re.emese@gmail.com>
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Cc: Emese Revfy <re.emese@gmail.com>
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Cc: PaX Team <pageexec@freemail.hu>
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Cc: stable@vger.kernel.org
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---
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v2:
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- clarify commit, explain use of #ifdef.
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---
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kernel/signal.c | 3 +++
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1 file changed, 3 insertions(+)
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diff --git a/kernel/signal.c b/kernel/signal.c
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index 2ec870a..8c8e3ca 100644
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--- a/kernel/signal.c
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+++ b/kernel/signal.c
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@@ -485,6 +485,9 @@ flush_signal_handlers(struct task_struct *t, int force_default)
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if (force_default || ka->sa.sa_handler != SIG_IGN)
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ka->sa.sa_handler = SIG_DFL;
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ka->sa.sa_flags = 0;
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+#ifdef __ARCH_HAS_SA_RESTORER
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+ ka->sa.sa_restorer = NULL;
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+#endif
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sigemptyset(&ka->sa.sa_mask);
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ka++;
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}
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--
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1.7.9.5
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18917ef |
--
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Kees Cook
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Chrome OS Security
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--
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