[libxslt] Fix double free in libexslt hash functions

[Nick Wellnhofer <nwellnhof src gnome org>]

commit d8862309f08054218b28e2c8f5fb3cb2f650cac7
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Wed Apr 20 14:35:43 2016 +0200

    Fix double free in libexslt hash functions
    
    Thanks to Nicolas Gregoire for the report.
    
    Fixes bug #765271:
    
    https://bugzilla.gnome.org/show_bug.cgi?id=765271

 libexslt/crypto.c             |   15 +++------------
 tests/exslt/crypto/hash.1.out |    2 ++
 tests/exslt/crypto/hash.1.xml |    5 +++++
 3 files changed, 10 insertions(+), 12 deletions(-)
---
diff --git a/libexslt/crypto.c b/libexslt/crypto.c
index 6aa9dd2..e13db8b 100644
--- a/libexslt/crypto.c
+++ b/libexslt/crypto.c
@@ -499,11 +499,8 @@ exsltCryptoMd4Function (xmlXPathParserContextPtr ctxt, int nargs) {
     unsigned char hex[MD5_DIGEST_LENGTH * 2 + 1];
 
     str_len = exsltCryptoPopString (ctxt, nargs, &str);
-    if (str_len == 0) {
-       xmlXPathReturnEmptyString (ctxt);
-       xmlFree (str);
+    if (str_len == 0)
        return;
-    }
 
     PLATFORM_HASH (ctxt, PLATFORM_MD4, (const char *) str, str_len,
                   (char *) hash);
@@ -532,11 +529,8 @@ exsltCryptoMd5Function (xmlXPathParserContextPtr ctxt, int nargs) {
     unsigned char hex[MD5_DIGEST_LENGTH * 2 + 1];
 
     str_len = exsltCryptoPopString (ctxt, nargs, &str);
-    if (str_len == 0) {
-       xmlXPathReturnEmptyString (ctxt);
-       xmlFree (str);
+    if (str_len == 0)
        return;
-    }
 
     PLATFORM_HASH (ctxt, PLATFORM_MD5, (const char *) str, str_len,
                   (char *) hash);
@@ -565,11 +559,8 @@ exsltCryptoSha1Function (xmlXPathParserContextPtr ctxt, int nargs) {
     unsigned char hex[SHA1_DIGEST_LENGTH * 2 + 1];
 
     str_len = exsltCryptoPopString (ctxt, nargs, &str);
-    if (str_len == 0) {
-       xmlXPathReturnEmptyString (ctxt);
-       xmlFree (str);
+    if (str_len == 0)
        return;
-    }
 
     PLATFORM_HASH (ctxt, PLATFORM_SHA1, (const char *) str, str_len,
                   (char *) hash);
diff --git a/tests/exslt/crypto/hash.1.out b/tests/exslt/crypto/hash.1.out
index a3b93d1..ce6f6ab 100644
--- a/tests/exslt/crypto/hash.1.out
+++ b/tests/exslt/crypto/hash.1.out
@@ -17,3 +17,5 @@ text = _Hello, World._     md5 = e9db5cf8349b1166e96a742e198a0dd1     sha1 = 179
 text = _Hello, World9_     md5 = faf56df200d7f645a7911c4179614ca8     sha1 = 
8a420fad2ccc0504448871245cb5769a42a16cdb
 text = _Hello, WorldЖ_     md5 = ffa8f2b84083d767a672debbe535a68e     sha1 = 
4a57c7b5874d38a98b6de30496fd51894039334f
 text = _Hello, WorldZ_     md5 = d6ec5883599d8ad6da7a32a094c1375b     sha1 = 
cdc052e9c8e42b61fd3d45c72211b4d0bafcd39f
+
+text = __     md5 =      sha1 = 
diff --git a/tests/exslt/crypto/hash.1.xml b/tests/exslt/crypto/hash.1.xml
index 57bf45f..a9a792d 100644
--- a/tests/exslt/crypto/hash.1.xml
+++ b/tests/exslt/crypto/hash.1.xml
@@ -23,4 +23,9 @@
        <pattern>Hello, WorldЖ</pattern>
        <pattern>Hello, WorldZ</pattern>
 
+       <br/>
+
+        <!-- Empty string. -->
+        <pattern/>
+
 </patterns>