From 9e9d78057dd0292ce226bc7f33844d49a7e79192 Mon Sep 17 00:00:00 2001
From: Michal Privoznik <mprivozn@redhat.com>
Date: Sat, 19 Oct 2019 12:09:32 +0200
Subject: [PATCH] src: Don't rely on virAsprintf() returning string length
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

In a few places our code relies on the fact that virAsprintf()
not only prints to allocated string but also that it returns the
length of that string. Fortunately, only few such places were
identified:

  https://www.redhat.com/archives/libvir-list/2019-September/msg01382.html

In case of virNWFilterSnoopLeaseFileWrite() and virFilePrintf()
we can use strlen() right after virAsprintf() to calculate the
length. In case of virDoubleToStr() it's only caller checks for
error case only, so we can limit the set of returned values to
just [-1, 0].

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
---
 src/nwfilter/nwfilter_dhcpsnoop.c |  7 +++----
 src/util/virfile.c                |  5 +++--
 src/util/virstring.c              | 10 ++++++----
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/src/nwfilter/nwfilter_dhcpsnoop.c b/src/nwfilter/nwfilter_dhcpsnoop.c
index bf25345e2c..665e7bff9c 100644
--- a/src/nwfilter/nwfilter_dhcpsnoop.c
+++ b/src/nwfilter/nwfilter_dhcpsnoop.c
@@ -1766,13 +1766,12 @@ virNWFilterSnoopLeaseFileWrite(int lfd, const char *ifkey,
     }
 
     /* time intf ip dhcpserver */
-    len = virAsprintf(&lbuf, "%u %s %s %s\n", ipl->timeout,
-                      ifkey, ipstr, dhcpstr);
-
-    if (len < 0) {
+    if (virAsprintf(&lbuf, "%u %s %s %s\n", ipl->timeout,
+                    ifkey, ipstr, dhcpstr) < 0) {
         ret = -1;
         goto cleanup;
     }
+    len = strlen(lbuf);
 
     if (safewrite(lfd, lbuf, len) != len) {
         virReportSystemError(errno, "%s", _("lease file write failed"));
diff --git a/src/util/virfile.c b/src/util/virfile.c
index c4d544be73..7c97317994 100644
--- a/src/util/virfile.c
+++ b/src/util/virfile.c
@@ -3394,12 +3394,13 @@ int virFilePrintf(FILE *fp, const char *msg, ...)
 {
     va_list vargs;
     g_autofree char *str = NULL;
-    int ret;
+    int ret = -1;
 
     va_start(vargs, msg);
 
-    if ((ret = virVasprintf(&str, msg, vargs)) < 0)
+    if (virVasprintf(&str, msg, vargs) < 0)
         goto cleanup;
+    ret = strlen(str);
 
     if (fwrite(str, 1, ret, fp) != ret) {
         virReportSystemError(errno, "%s",
diff --git a/src/util/virstring.c b/src/util/virstring.c
index 1494eab132..52e36fe4da 100644
--- a/src/util/virstring.c
+++ b/src/util/virstring.c
@@ -703,23 +703,25 @@ virStrToDouble(char const *s,
  *
  * converts double to string with C locale (thread-safe).
  *
- * Returns -1 on error, size of the string otherwise.
+ * Returns: 0 on success, -1 otherwise.
  */
 int
 virDoubleToStr(char **strp, double number)
 {
     virLocale oldlocale;
-    int ret = -1;
+    int rc;
 
     if (virLocaleSetRaw(&oldlocale) < 0)
         return -1;
 
-    ret = virAsprintf(strp, "%lf", number);
+    rc = virAsprintf(strp, "%lf", number);
 
     virLocaleRevert(&oldlocale);
     virLocaleFixupRadix(strp);
 
-    return ret;
+    if (rc < 0)
+        return -1;
+    return 0;
 }