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authorKees Cook <keescook@chromium.org>2013-03-13 14:59:33 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-03-13 15:21:44 -0700
commit2ca39528c01a933f6689cd6505ce65bd6d68a530 (patch)
treedac5eb0adf524fcfe14558ad8e24b076f61951e4 /kernel
parentf8749452adcddd62e3707709ec2ae4856e70a3f2 (diff)
downloadvexpress-lsk-2ca39528c01a933f6689cd6505ce65bd6d68a530.tar.gz
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 ... [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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/signal.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index d63c79e7e41..43b0d4a1b7b 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++;
}