[PATCH 1/3] signal(i386): alternative signal stack wraparound occurs

[Shi Weihua <shiwh@cn.fujitsu.com>]

Fixing alternative signal stack wraparound.

If a process uses alternative signal stack by using sigaltstack()
and that stack overflow, stack wraparound occurs.
This patch checks whether the signal frame is on the alternative
stack. If the frame is not on there, kill a signal SIGSEGV to the process forcedly
then the process will be terminated.

This patch is for i386,version is 2.6.23-rc8.

Signed-off-by: Shi Weihua <shiwh@cn.fujitsu.com>

diff -pur linux-2.6.23-rc8.orig/arch/i386/kernel/signal.c linux-2.6.23-rc8/arch/i386/kernel/signal.c
--- linux-2.6.23-rc8.orig/arch/i386/kernel/signal.c	2007-09-26 09:44:08.000000000 +0900
+++ linux-2.6.23-rc8/arch/i386/kernel/signal.c	2007-09-26 13:14:25.000000000 +0900
@@ -332,6 +332,10 @@ static int setup_frame(int sig, struct k

  	frame = get_sigframe(ka, regs, sizeof(*frame));

+	if ((ka->sa.sa_flags & SA_ONSTACK) &&
+		!sas_ss_flags((unsigned long)frame))
+		goto give_sigsegv;
+
  	if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
  		goto give_sigsegv;

@@ -425,6 +429,10 @@ static int setup_rt_frame(int sig, struc

  	frame = get_sigframe(ka, regs, sizeof(*frame));

+	if ((ka->sa.sa_flags & SA_ONSTACK) &&
+		!sas_ss_flags((unsigned long)frame))
+		goto give_sigsegv;
+
  	if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
  		goto give_sigsegv;