don't try writing past the end unless we have to

ok gilles millert

1 files changed, 16 insertions, 8 deletions

diff --git a/src/lib/libc/net/base64.c b/src/lib/libc/net/base64.c
index 78ef449a75..7c3d1d319f 100644
--- a/src/lib/libc/net/base64.c
+++ b/src/lib/libc/net/base64.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: base64.c,v 1.6 2013/11/24 23:51:28 deraadt Exp $      */
+/*      $OpenBSD: base64.c,v 1.7 2013/12/31 02:32:56 tedu Exp $ */
 
 /*
  * Copyright (c) 1996 by Internet Software Consortium.
@@ -194,6 +194,7 @@ b64_pton(src, target, targsize)
         size_t targsize;
 {
         int tarindex, state, ch;
+        u_char nextbyte;
         char *pos;
 
         state = 0;
@@ -221,22 +222,28 @@ b64_pton(src, target, targsize)
                         break;
                 case 1:
                         if (target) {
-                                if (tarindex + 1 >= targsize)
+                                if (tarindex >= targsize)
                                         return (-1);
                                 target[tarindex]   |=  (pos - Base64) >> 4;
-                                target[tarindex+1]  = ((pos - Base64) & 0x0f)
-                                                        << 4 ;
+                                nextbyte = ((pos - Base64) & 0x0f) << 4;
+                                if (tarindex + 1 < targsize)
+                                        target[tarindex+1] = nextbyte;
+                                else if (nextbyte)
+                                        return (-1);
                         }
                         tarindex++;
                         state = 2;
                         break;
                 case 2:
                         if (target) {
-                                if (tarindex + 1 >= targsize)
+                                if (tarindex >= targsize)
                                         return (-1);
                                 target[tarindex]   |=  (pos - Base64) >> 2;
-                                target[tarindex+1]  = ((pos - Base64) & 0x03)
-                                                        << 6;
+                                nextbyte = ((pos - Base64) & 0x03) << 6;
+                                if (tarindex + 1 < targsize)
+                                        target[tarindex+1] = nextbyte;
+                                else if (nextbyte)
+                                        return (-1);
                         }
                         tarindex++;
                         state = 3;
@@ -292,7 +299,8 @@ b64_pton(src, target, targsize)
                          * zeros.  If we don't check them, they become a
                          * subliminal channel.
                          */
-                        if (target && target[tarindex] != 0)
+                        if (target && tarindex < targsize &&
+                            target[tarindex] != 0)
                                 return (-1);
                 }
         } else {