[PATCH 4/6] UML - Don't allow processes to call into stub

[Jeff Dike <jdike@addtoit.com>]

Kill a process that tries to branch into a stub and execute a system
call.  There are no security implications here - a system call in a
stub is treated the same as a system call anywhere else.  But if a
process is trying to branch into a stub, either it is trying something
nasty or it has gone haywire, so it's a good idea to get rid of it in
either case.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
---
 arch/um/os-Linux/skas/process.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-2.6.22/arch/um/os-Linux/skas/process.c
===================================================================
--- linux-2.6.22.orig/arch/um/os-Linux/skas/process.c	2007-12-05 12:51:53.000000000 -0500
+++ linux-2.6.22/arch/um/os-Linux/skas/process.c	2007-12-05 16:34:55.000000000 -0500
@@ -146,6 +146,9 @@ static void handle_trap(int pid, struct 
 {
 	int err, status;
 
+	if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
+		fatal_sigsegv();
+
 	/* Mark this as a syscall */
 	UPT_SYSCALL_NR(regs) = PT_SYSCALL_NR(regs->gp);
 
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