[tor-commits] [tor/master] scan-build: memarea_strndup() undefined behavior

[nickm at torproject.org]

commit 3b1f7f75a7efa51ae5549a6413e90066cfe307a8
Author: Nick Mathewson <nickm at torproject.org>
Date:   Sat Apr 19 13:16:56 2014 -0400

    scan-build: memarea_strndup() undefined behavior
    
    The memarea_strndup() function would have hit undefined behavior by
    creating an 'end' pointer off the end of a string if it had ever been
    given an 'n' argument bigger than the length of the memory ares that
    it's scanning.  Fortunately, we never did that except in the unit
    tests.  But it's not a safe behavior to leave lying around.
---
 src/common/memarea.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/src/common/memarea.c b/src/common/memarea.c
index e2d07fc..bcaea09 100644
--- a/src/common/memarea.c
+++ b/src/common/memarea.c
@@ -291,14 +291,11 @@ memarea_strdup(memarea_t *area, const char *s)
 char *
 memarea_strndup(memarea_t *area, const char *s, size_t n)
 {
-  size_t ln;
+  size_t ln = 0;
   char *result;
-  const char *cp, *end = s+n;
   tor_assert(n < SIZE_T_CEILING);
-  for (cp = s; cp < end && *cp; ++cp)
+  for (ln = 0; ln < n && s[ln]; ++ln)
     ;
-  /* cp now points to s+n, or to the 0 in the string. */
-  ln = cp-s;
   result = memarea_alloc(area, ln+1);
   memcpy(result, s, ln);
   result[ln]='\0';