m32r: hole in shifting pc back

It's a userland pointer; worse, an untrustable one since ptrace
has just provided a chance to modify it.

X-Roothole-Covering-Cabal: TINRCC
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 17 insertions, 21 deletions

diff --git a/arch/m32r/kernel/signal.c b/arch/m32r/kernel/signal.c
index a56fcbd8abe6..7bbe38645ed5 100644
--- a/arch/m32r/kernel/signal.c
+++ b/arch/m32r/kernel/signal.c
@@ -251,6 +251,19 @@ give_sigsegv:
         return -EFAULT;
 }
 
+static int prev_insn(struct pt_regs *regs)
+{
+        u16 inst;
+        if (get_user(&inst, (u16 __user *)(regs->bpc - 2)))
+                return -EFAULT;
+        if ((inst & 0xfff0) == 0x10f0)  /* trap ? */
+                regs->bpc -= 2;
+        else
+                regs->bpc -= 4;
+        regs->syscall_nr = -1;
+        return 0;
+}
+
 /*
  * OK, we're invoking a handler
  */
@@ -259,8 +272,6 @@ static int
 handle_signal(unsigned long sig, struct k_sigaction *ka, siginfo_t *info,
               sigset_t *oldset, struct pt_regs *regs)
 {
-        unsigned short inst;
-
         /* Are we from a system call? */
         if (regs->syscall_nr >= 0) {
                 /* If so, check system call restarting.. */
@@ -278,12 +289,8 @@ handle_signal(unsigned long sig, struct k_sigaction *ka, siginfo_t *info,
                         /* fallthrough */
                         case -ERESTARTNOINTR:
                                 regs->r0 = regs->orig_r0;
-                                inst = *(unsigned short *)(regs->bpc - 2);
-                                if ((inst & 0xfff0) == 0x10f0)  /* trap ? */
-                                        regs->bpc -= 2;
-                                else
-                                        regs->bpc -= 4;
-                                regs->syscall_nr = -1;
+                                if (prev_insn(regs) < 0)
+                                        return -EFAULT;
                 }
         }
 
@@ -310,7 +317,6 @@ static void do_signal(struct pt_regs *regs)
         siginfo_t info;
         int signr;
         struct k_sigaction ka;
-        unsigned short inst;
         sigset_t *oldset;
 
         /*
@@ -353,21 +359,11 @@ static void do_signal(struct pt_regs *regs)
                     regs->r0 == -ERESTARTSYS ||
                     regs->r0 == -ERESTARTNOINTR) {
                         regs->r0 = regs->orig_r0;
-                        inst = *(unsigned short *)(regs->bpc - 2);
-                        if ((inst & 0xfff0) == 0x10f0)  /* trap ? */
-                                regs->bpc -= 2;
-                        else
-                                regs->bpc -= 4;
-                        regs->syscall_nr = -1;
+                        prev_insn(regs);
                 } else if (regs->r0 == -ERESTART_RESTARTBLOCK){
                         regs->r0 = regs->orig_r0;
                         regs->r7 = __NR_restart_syscall;
-                        inst = *(unsigned short *)(regs->bpc - 2);
-                        if ((inst & 0xfff0) == 0x10f0)  /* trap ? */
-                                regs->bpc -= 2;
-                        else
-                                regs->bpc -= 4;
-                        regs->syscall_nr = -1;
+                        prev_insn(regs);
                 }
         }
         if (test_thread_flag(TIF_RESTORE_SIGMASK)) {