[patch 2/5] Instantiate comments in ip(6)tables rules

[Stefan Berger <stefanb@xxxxxxxxxx>]

In this patch I am extending the rule instantiator to create the comment
node where supported, which is the case for iptables and ip6tables.

Since commands are written in the format

cmd="iptables ...-m comment --comment \"\" "

certain characters ("$`\) in the comment need to be escaped (twice) to
prevent comments from becoming commands themselves or cause other
forms of (bash) substitutions. I have tested this with various input and in
my tests the input made it straight into the comment. A test case for TCK
will be provided separately that tests this.

To prevent consecutive spaces in comments from becoming a single space
(by bash), the IFS variable is now set to an empty string. Also, commands
are now executed using bash's 'eval' command.

Since the regular strchr() function causes a compiler warning when neither
one of the parameters is a constant, I reimplemented this function and
called it _strchr(). Here is the reference to this bug

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36513


Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxx>

---
 src/nwfilter/nwfilter_ebiptables_driver.c |   68 +++++++++++++++++++++++++++++-
 src/nwfilter/nwfilter_ebiptables_driver.h |    3 +
 2 files changed, 69 insertions(+), 2 deletions(-)

Index: libvirt-acl/src/nwfilter/nwfilter_ebiptables_driver.c
===================================================================
--- libvirt-acl.orig/src/nwfilter/nwfilter_ebiptables_driver.c
+++ libvirt-acl/src/nwfilter/nwfilter_ebiptables_driver.c
@@ -55,7 +55,7 @@
 #define CMD_DEF_PRE  "cmd=\""
 #define CMD_DEF_POST "\""
 #define CMD_DEF(X) CMD_DEF_PRE X CMD_DEF_POST
-#define CMD_EXEC   "res=`${cmd}`" CMD_SEPARATOR
+#define CMD_EXEC   "res=`eval ${cmd}`" CMD_SEPARATOR
 #define CMD_STOPONERR(X) \
     X ? "if [ $? -ne 0 ]; then" \
         "  echo \"Failure to execute command '${cmd}'.\";" \
@@ -291,6 +291,58 @@ printDataTypeAsHex(virNWFilterHashTableP
 }
 
 
+/* avoiding a compiler warning trough own implementation */
+static const char *
+_strchr(const char *s, int c)
+{
+    while (*s && *s != (char)c)
+        s++;
+    if (*s)
+        return s;
+    return NULL;
+}
+
+
+static char *
+shellEscapeString(const char *data, size_t maxlen,
+                  const char *s, bool doubleEscape)
+{
+    char *res;
+    size_t i, j, add = 0, len = strlen(data);
+
+    if (len > maxlen)
+        len = maxlen;
+
+    for (i = 0; i < len; i++) {
+        if (_strchr(s, data[i])) {
+            add += 1;
+            if (doubleEscape)
+                add += 2;
+        }
+    }
+
+    if (VIR_ALLOC_VAR(res, char, len+add+1) < 0) {
+        virReportOOMError();
+        return NULL;
+    }
+
+    j = 0;
+    for (i = 0; i < len; i++) {
+        if (_strchr(s, data[i])) {
+            res[j++] = '\\';
+            if (doubleEscape) {
+                res[j++] = '\\';
+                res[j++] = '\\';
+            }
+        }
+        res[j++] = data[i];
+    }
+    res[j] = 0;
+
+    return res;
+}
+
+
 static void
 ebiptablesRuleInstFree(ebiptablesRuleInstPtr inst)
 {
@@ -993,6 +1045,18 @@ iptablesHandleIpHdr(virBufferPtr buf,
         }
     }
 
+    if (HAS_ENTRY_ITEM(&ipHdr->dataComment)) {
+        char *cmt = shellEscapeString(ipHdr->dataComment.u.string,
+                                      IPTABLES_MAX_COMMENT_SIZE,
+                                      "\"`\\$", true);
+        if (!cmt)
+            goto err_exit;
+        virBufferVSprintf(buf,
+                          " -m comment --comment \\\"%s\\\"",
+                          cmt);
+        VIR_FREE(cmt);
+    }
+
     return 0;
 
 err_exit:
@@ -2211,7 +2275,7 @@ ebiptablesWriteToTempFile(const char *st
     char *header;
     size_t written;
 
-    virBufferVSprintf(&buf, "#!%s\n", bash_cmd_path);
+    virBufferVSprintf(&buf, "#!%s\nIFS=""\n", bash_cmd_path);
 
     if (virBufferError(&buf)) {
         virBufferFreeAndReset(&buf);
Index: libvirt-acl/src/nwfilter/nwfilter_ebiptables_driver.h
===================================================================
--- libvirt-acl.orig/src/nwfilter/nwfilter_ebiptables_driver.h
+++ libvirt-acl/src/nwfilter/nwfilter_ebiptables_driver.h
@@ -45,4 +45,7 @@ extern virNWFilterTechDriver ebiptables_
 
 # define EBIPTABLES_DRIVER_ID "ebiptables"
 
+
+# define IPTABLES_MAX_COMMENT_SIZE  256
+
 #endif

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