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+ signal-always-clear-sa_restorer-on-execve.patch added to -mm tree

The patch titled
     Subject: signal: always clear sa_restorer on execve
has been added to the -mm tree.  Its filename is

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From: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: signal: always clear sa_restorer on execve

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

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reported-by: Emese Revfy <re.emese@xxxxxxxxx>
Cc: Emese Revfy <re.emese@xxxxxxxxx>
Cc: PaX Team <pageexec@xxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Cc: Julien Tinnes <jln@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

 kernel/signal.c |    3 +++
 1 file changed, 3 insertions(+)

diff -puN kernel/signal.c~signal-always-clear-sa_restorer-on-execve kernel/signal.c
--- a/kernel/signal.c~signal-always-clear-sa_restorer-on-execve
+++ a/kernel/signal.c
@@ -485,6 +485,9 @@ flush_signal_handlers(struct task_struct
 		if (force_default || ka->sa.sa_handler != SIG_IGN)
 			ka->sa.sa_handler = SIG_DFL;
 		ka->sa.sa_flags = 0;
+		ka->sa.sa_restorer = NULL;

Patches currently in -mm which might be from keescook@xxxxxxxxxxxx are


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