mutt: Fix potential memory leak in rfc2047_encode. (closes #3825)

[Brendan Cully]

changeset: 6611:b8240918eded
user:      Kevin McCarthy <ke...@8t8.us>
date:      Fri Apr 08 18:38:27 2016 -0700
link:      http://dev.mutt.org/hg/mutt/rev/b8240918eded

Fix potential memory leak in rfc2047_encode.  (closes #3825)

If convert_string() has nonreversible characters, the allocated output
buffer would be overwritten (and not freed) in rfc2047_encode().

Thanks to Richard Russon for the bug report and initial patch, and to
TAKAHASHI Tamotsu for the analysis and revised fix suggestion.

diffs (21 lines):

diff -r 180a90d05ed4 -r b8240918eded rfc2047.c
--- a/rfc2047.c Fri Apr 08 15:27:17 2016 -0700
+++ b/rfc2047.c Fri Apr 08 18:38:27 2016 -0700
@@ -410,7 +410,7 @@
   int ret = 0;
   char *buf;
   size_t bufpos, buflen;
-  char *u, *t0, *t1, *t;
+  char *u = NULL, *t0, *t1, *t;
   char *s0, *s1;
   size_t ulen, r, n, wlen;
   encoder_t encoder;
@@ -423,7 +423,7 @@
   {
     ret = 1; 
     icode = 0;
-    u = safe_malloc ((ulen = dlen) + 1);
+    safe_realloc (&u, (ulen = dlen) + 1);
     memcpy (u, d, dlen);
     u[ulen] = 0;
   }