[tor-commits] [tor/release-0.3.3] Fix possible UB in an end-of-string check in get_next_token().

[nickm at torproject.org]

commit 368413a321a65234c0256c4ea80c613207cf7587
Author: Nick Mathewson <nickm at torproject.org>
Date:   Thu Oct 25 09:06:13 2018 -0400

    Fix possible UB in an end-of-string check in get_next_token().
    
    Remember, you can't check to see if there are N bytes left in a
    buffer by doing (buf + N < end), since the buf + N computation might
    take you off the end of the buffer and result in undefined behavior.
    
    Fixes 28202; bugfix on 0.2.0.3-alpha.
---
 changes/bug28202     | 4 ++++
 src/or/routerparse.c | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/changes/bug28202 b/changes/bug28202
new file mode 100644
index 000000000..182daac4f
--- /dev/null
+++ b/changes/bug28202
@@ -0,0 +1,4 @@
+  o Minor bugfixes (C correctness):
+    - Avoid undefined behavior in an end-of-string check when parsing the
+      BEGIN line in a directory object.  Fixes bug 28202; bugfix on
+      0.2.0.3-alpha.
diff --git a/src/or/routerparse.c b/src/or/routerparse.c
index 521e237be..063cbbcda 100644
--- a/src/or/routerparse.c
+++ b/src/or/routerparse.c
@@ -4964,7 +4964,7 @@ get_next_token(memarea_t *area,
     goto check_object;
 
   obstart = *s; /* Set obstart to start of object spec */
-  if (*s+16 >= eol || memchr(*s+11,'\0',eol-*s-16) || /* no short lines, */
+  if (eol - *s <= 16 || memchr(*s+11,'\0',eol-*s-16) || /* no short lines, */
       strcmp_len(eol-5, "-----", 5) ||           /* nuls or invalid endings */
       (eol-*s) > MAX_UNPARSED_OBJECT_SIZE) {     /* name too long */
     RET_ERR("Malformed object: bad begin line");