[tor-commits] [tor/release-0.2.5] Check for len < 4 in dn_indicates_v3_cert

[nickm at torproject.org]

commit 35bf07b8d67d018f7740ca195cf8c7c86b1b4ef9
Author: Nick Mathewson <nickm at torproject.org>
Date:   Wed Oct 21 11:44:43 2015 -0400

    Check for len < 4 in dn_indicates_v3_cert
    
    Without this check, we potentially look up to 3 characters before
    the start of a malloc'd segment, which could provoke a crash under
    certain (weird afaik) circumstances.
    
    Fixes 17404; bugfix on 0.2.6.3-alpha.
---
 changes/bug17404    | 6 ++++++
 src/common/tortls.c | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/changes/bug17404 b/changes/bug17404
new file mode 100644
index 0000000..d524f66
--- /dev/null
+++ b/changes/bug17404
@@ -0,0 +1,6 @@
+  o Major bugfixes (security, correctness):
+    - Fix a programming error that could cause us to read 4 bytes before
+      the beginning of an openssl string. This could be used to provoke
+      a crash on systems with an unusual malloc implementation, or
+      systems with unsual hardening installed. Fixes bug 17404; bugfix
+      on 0.2.3.6-alpha.
diff --git a/src/common/tortls.c b/src/common/tortls.c
index 4222f6d..75ca47d 100644
--- a/src/common/tortls.c
+++ b/src/common/tortls.c
@@ -2676,6 +2676,10 @@ dn_indicates_v3_cert(X509_NAME *name)
   len = ASN1_STRING_to_UTF8(&s, str);
   if (len < 0)
     return 0;
+  if (len < 4) {
+    OPENSSL_free(s);
+    return 0;
+  }
   r = fast_memneq(s + len - 4, ".net", 4);
   OPENSSL_free(s);
   return r;