Fix array overflow in backtrace on PowerPC (bug 25423)

When unwinding through a signal frame the backtrace function on PowerPC
didn't check array bounds when storing the frame address.  Fixes commit
d400dcac5e ("PowerPC: fix backtrace to handle signal trampolines").

(cherry picked from commit d93769405996dfc11d216ddbe415946617b5a494)

4 files changed, 17 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index ace1b86fdb..038541c83b 100644
--- a/NEWS
+++ b/NEWS
@@ -73,6 +73,7 @@ The following bugs are resolved with this release:
   [25204] Ignore LD_PREFER_MAP_32BIT_EXEC for SUID programs
   [25225] ld.so fails to link on x86 if GCC defaults to -fcf-protection
   [25232] No const correctness for strchr et al. for Clang++
+  [25423] Array overflow in backtrace on powerpc
 
 Security related changes:
 
diff --git a/debug/tst-backtrace5.c b/debug/tst-backtrace5.c
index 0e6fb1a024..a117f1544f 100644
--- a/debug/tst-backtrace5.c
+++ b/debug/tst-backtrace5.c
@@ -88,6 +88,18 @@ handle_signal (int signum)
       }
   /* Symbol names are not available for static functions, so we do not
      check do_test.  */
+
+  /* Check that backtrace does not return more than what fits in the array
+     (bug 25423).  */
+  for (int j = 0; j < NUM_FUNCTIONS; j++)
+    {
+      n = backtrace (addresses, j);
+      if (n > j)
+	{
+	  FAIL ();
+	  return;
+	}
+    }
 }
 
 NO_INLINE int
diff --git a/sysdeps/powerpc/powerpc32/backtrace.c b/sysdeps/powerpc/powerpc32/backtrace.c
index 5422fdd50d..c7b64f9e9b 100644
--- a/sysdeps/powerpc/powerpc32/backtrace.c
+++ b/sysdeps/powerpc/powerpc32/backtrace.c
@@ -114,6 +114,8 @@ __backtrace (void **array, int size)
         }
       if (gregset)
 	{
+	  if (count + 1 == size)
+	    break;
 	  array[++count] = (void*)((*gregset)[PT_NIP]);
 	  current = (void*)((*gregset)[PT_R1]);
 	}
diff --git a/sysdeps/powerpc/powerpc64/backtrace.c b/sysdeps/powerpc/powerpc64/backtrace.c
index c0c4b48262..0acf17b37e 100644
--- a/sysdeps/powerpc/powerpc64/backtrace.c
+++ b/sysdeps/powerpc/powerpc64/backtrace.c
@@ -87,6 +87,8 @@ __backtrace (void **array, int size)
       if (is_sigtramp_address (current->return_address))
         {
 	  struct signal_frame_64 *sigframe = (struct signal_frame_64*) current;
+	  if (count + 1 == size)
+	    break;
           array[++count] = (void*) sigframe->uc.uc_mcontext.gp_regs[PT_NIP];
 	  current = (void*) sigframe->uc.uc_mcontext.gp_regs[PT_R1];
 	}