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Subject[PATCH] signal: always clear sa_restorer on execve
When the new signal handlers are set up for a fork, 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().

$ 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
...
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: stable@vger.kernel.org
---
kernel/signal.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/signal.c b/kernel/signal.c
index 2ec870a..8c8e3ca 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 __ARCH_HAS_SA_RESTORER
+ ka->sa.sa_restorer = NULL;
+#endif
sigemptyset(&ka->sa.sa_mask);
ka++;
}
--
1.7.9.5

--
Kees Cook
Chrome OS Security


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