powerpc/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: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org

diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index ed799e9947737084a02183ddee12bd1a93d7e4ac..5dc47ebb3840144aee53b0f75ea31d9e37a643d5 100644 (file)
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -1788,7 +1788,7 @@ static int do_seccomp(struct pt_regs *regs)
 
        /*
         * The syscall was allowed by seccomp, restore the register
-        * state to what ptrace and audit expect.
+        * state to what audit expects.
         * Note that we use orig_gpr3, which means a seccomp tracer can
         * modify the first syscall parameter (in orig_gpr3) and also
         * allow the syscall to proceed.
@@ -1822,22 +1822,25 @@ static inline int do_seccomp(struct pt_regs *regs) { return 0; }
  */
 long do_syscall_trace_enter(struct pt_regs *regs)
 {
-       bool abort = false;
-
        user_exit();
 
+       /*
+        * The tracer may decide to abort the syscall, if so tracehook
+        * will return !0. Note that the tracer may also just change
+        * regs->gpr[0] to an invalid syscall number, that is handled
+        * below on the exit path.
+        */
+       if (test_thread_flag(TIF_SYSCALL_TRACE) &&
+           tracehook_report_syscall_entry(regs))
+               goto skip;
+
+       /* Run seccomp after ptrace; allow it to set gpr[3]. */
        if (do_seccomp(regs))
                return -1;
 
-       if (test_thread_flag(TIF_SYSCALL_TRACE)) {
-               /*
-                * The tracer may decide to abort the syscall, if so tracehook
-                * will return !0. Note that the tracer may also just change
-                * regs->gpr[0] to an invalid syscall number, that is handled
-                * below on the exit path.
-                */
-               abort = tracehook_report_syscall_entry(regs) != 0;
-       }
+       /* Avoid trace and audit when syscall is invalid. */
+       if (regs->gpr[0] >= NR_syscalls)
+               goto skip;
 
        if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
                trace_sys_enter(regs, regs->gpr[0]);
@@ -1854,17 +1857,16 @@ long do_syscall_trace_enter(struct pt_regs *regs)
                                    regs->gpr[5] & 0xffffffff,
                                    regs->gpr[6] & 0xffffffff);
 
-       if (abort || regs->gpr[0] >= NR_syscalls) {
-               /*
-                * If we are aborting explicitly, or if the syscall number is
-                * now invalid, set the return value to -ENOSYS.
-                */
-               regs->gpr[3] = -ENOSYS;
-               return -1;
-       }
-
        /* Return the possibly modified but valid syscall number */
        return regs->gpr[0];
+
+skip:
+       /*
+        * If we are aborting explicitly, or if the syscall number is
+        * now invalid, set the return value to -ENOSYS.
+        */
+       regs->gpr[3] = -ENOSYS;
+       return -1;
 }
 
 void do_syscall_trace_leave(struct pt_regs *regs)