s390/ptrace: run seccomp after ptrace

Close the hole where ptrace can change a syscall out from under seccomp.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: linux-s390@vger.kernel.org

diff --git a/arch/s390/kernel/ptrace.c b/arch/s390/kernel/ptrace.c
index c238e99..cea1701 100644 (file)
--- a/arch/s390/kernel/ptrace.c
+++ b/arch/s390/kernel/ptrace.c
@@ -821,15 +821,6 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 
 asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
 {
-       long ret = 0;
-
-       /* Do the secure computing check first. */
-       if (secure_computing(NULL)) {
-               /* seccomp failures shouldn't expose any additional code. */
-               ret = -1;
-               goto out;
-       }
-
        /*
         * The sysc_tracesys code in entry.S stored the system
         * call number to gprs[2].
@@ -843,7 +834,13 @@ asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
                 * the system call and the system call restart handling.
                 */
                clear_pt_regs_flag(regs, PIF_SYSCALL);
-               ret = -1;
+               return -1;
+       }
+
+       /* Do the secure computing check after ptrace. */
+       if (secure_computing(NULL)) {
+               /* seccomp failures shouldn't expose any additional code. */
+               return -1;
        }
 
        if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
@@ -852,8 +849,8 @@ asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
        audit_syscall_entry(regs->gprs[2], regs->orig_gpr2,
                            regs->gprs[3], regs->gprs[4],
                            regs->gprs[5]);
-out:
-       return ret ?: regs->gprs[2];
+
+       return regs->gprs[2];
 }
 
 asmlinkage void do_syscall_trace_exit(struct pt_regs *regs)