[Emacs-diffs] /srv/bzr/emacs/trunk r104398: avoid a sign-extension bug in crypto_hash_function

[Jim Meyering]

------------------------------------------------------------
revno: 104398
committer: Jim Meyering <address@hidden>
branch nick: trunk
timestamp: Sat 2011-05-28 14:19:08 +0200
message:
  avoid a sign-extension bug in crypto_hash_function
  
  * fns.c (to_uchar): Define.
  (crypto_hash_function): Use it to convert some newly-signed
  variables to unsigned, to avoid sign-extension bugs.  For example,
  without this change, (md5 "truc") would evaluate to
  45723a2aff78ff4fff7fff1114760e62 rather than the expected
  45723a2af3788c4ff17f8d1114760e62.  Reported by Antoine Levitt in
  http://thread.gmane.org/gmane.emacs.devel/139824
modified:
  src/ChangeLog
  src/fns.c

=== modified file 'src/ChangeLog'
--- a/src/ChangeLog     2011-05-27 19:58:54 +0000
+++ b/src/ChangeLog     2011-05-28 12:19:08 +0000
@@ -1,3 +1,14 @@
+2011-05-28  Jim Meyering  <address@hidden>
+
+       avoid a sign-extension bug in crypto_hash_function
+       * fns.c (to_uchar): Define.
+       (crypto_hash_function): Use it to convert some newly-signed
+       variables to unsigned, to avoid sign-extension bugs.  For example,
+       without this change, (md5 "truc") would evaluate to
+       45723a2aff78ff4fff7fff1114760e62 rather than the expected
+       45723a2af3788c4ff17f8d1114760e62.  Reported by Antoine Levitt in
+       http://thread.gmane.org/gmane.emacs.devel/139824
+
 2011-05-27  Paul Eggert  <address@hidden>
 
        Integer overflow fixes.

=== modified file 'src/fns.c'
--- a/src/fns.c 2011-05-27 19:37:32 +0000
+++ b/src/fns.c 2011-05-28 12:19:08 +0000
@@ -4520,6 +4520,11 @@
 #include "md5.h"
 #include "sha1.h"
 
+/* Convert a possibly-signed character to an unsigned character.  This is
+   a bit safer than casting to unsigned char, since it catches some type
+   errors that the cast doesn't.  */
+static inline unsigned char to_uchar (char ch) { return ch; }
+
 /* TYPE: 0 for md5, 1 for sha1. */
 
 static Lisp_Object
@@ -4717,7 +4722,7 @@
          {
            char value[33];
            for (i = 0; i < 16; i++)
-             sprintf (&value[2 * i], "%02x", digest[i]);
+             sprintf (&value[2 * i], "%02x", to_uchar (digest[i]));
            res = make_string (value, 32);
          }
        else
@@ -4735,7 +4740,7 @@
          {
            char value[41];
            for (i = 0; i < 20; i++)
-             sprintf (&value[2 * i], "%02x", digest[i]);
+             sprintf (&value[2 * i], "%02x", to_uchar (digest[i]));
            res = make_string (value, 40);
          }
        else