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[libvirt] [PATCH 5/7] lxc: avoid large stacks with veth creation



* src/lxc/veth.h (vethCreate): Change prototype.
* src/lxc/veth.c (vethCreate): Always malloc veth2, and allocate
veth1 if needed.
(getFreeVethName): Adjust signature, and use virAsprintf.
* src/lxc/lxc_driver.c (lxcSetupInterfaces): Adjust caller.
---

This issue crossed file boundaries.  It was a bit tricky, since
vethCreate was used in two patterns - one where the parent name was
already known, and another where the parent name is picked as the
first available option.  But the end result avoids strdup'ing a
fixed-width buffer, and I think I correctly avoided any leaks (in
lxcSetupInterfaces, once a string is transferred to *veths, then
returning failure will cause that string to be freed in the caller).
It also gets rid of a PATH_MAX stack over-allocation.

 src/lxc/lxc_driver.c |   32 ++++++++-----------
 src/lxc/veth.c       |   84 ++++++++++++++++++++++++++++++-------------------
 src/lxc/veth.h       |    6 ++--
 3 files changed, 67 insertions(+), 55 deletions(-)

diff --git a/src/lxc/lxc_driver.c b/src/lxc/lxc_driver.c
index 6fe20b1..326fee6 100644
--- a/src/lxc/lxc_driver.c
+++ b/src/lxc/lxc_driver.c
@@ -812,14 +812,16 @@ static int lxcSetupInterfaces(virConnectPtr conn,
         return -1;

     for (i = 0 ; i < def->nnets ; i++) {
-        char parentVeth[PATH_MAX] = "";
-        char containerVeth[PATH_MAX] = "";
+        char *parentVeth;
+        char *containerVeth = NULL;

         switch (def->nets[i]->type) {
         case VIR_DOMAIN_NET_TYPE_NETWORK:
         {
-            virNetworkPtr network = virNetworkLookupByName(conn,
-                                                           def->nets[i]->data.network.name);
+            virNetworkPtr network;
+
+            network = virNetworkLookupByName(conn,
+                                             def->nets[i]->data.network.name);
             if (!network) {
                 goto error_exit;
             }
@@ -852,31 +854,23 @@ static int lxcSetupInterfaces(virConnectPtr conn,
         }

         DEBUG0("calling vethCreate()");
-        if (NULL != def->nets[i]->ifname) {
-            strcpy(parentVeth, def->nets[i]->ifname);
-        }
-        DEBUG("parentVeth: %s, containerVeth: %s", parentVeth, containerVeth);
-        if (vethCreate(parentVeth, PATH_MAX, containerVeth, PATH_MAX) < 0)
+        parentVeth = def->nets[i]->ifname;
+        if (vethCreate(&parentVeth, &containerVeth) < 0)
             goto error_exit;
+        DEBUG("parentVeth: %s, containerVeth: %s", parentVeth, containerVeth);

         if (NULL == def->nets[i]->ifname) {
-            def->nets[i]->ifname = strdup(parentVeth);
+            def->nets[i]->ifname = parentVeth;
         }
+
         if (VIR_REALLOC_N(*veths, (*nveths)+1) < 0) {
             virReportOOMError();
+            VIR_FREE(containerVeth);
             goto error_exit;
         }
-        if (((*veths)[(*nveths)] = strdup(containerVeth)) == NULL) {
-            virReportOOMError();
-            goto error_exit;
-        }
+        (*veths)[(*nveths)] = containerVeth;
         (*nveths)++;

-        if (NULL == def->nets[i]->ifname) {
-            virReportOOMError();
-            goto error_exit;
-        }
-
         {
             char macaddr[VIR_MAC_STRING_BUFLEN];
             virFormatMacAddr(def->nets[i]->mac, macaddr);
diff --git a/src/lxc/veth.c b/src/lxc/veth.c
index 5f038d6..14cfaa2 100644
--- a/src/lxc/veth.c
+++ b/src/lxc/veth.c
@@ -13,6 +13,7 @@
 #include <config.h>

 #include <string.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <sys/types.h>
 #include <sys/wait.h>
@@ -33,42 +34,46 @@
 /* Functions */
 /**
  * getFreeVethName:
- * @veth: name for veth device (NULL to find first open)
- * @maxLen: max length of veth name
+ * @veth: pointer to store returned name for veth device
  * @startDev: device number to start at (x in vethx)
  *
  * Looks in /sys/class/net/ to find the first available veth device
  * name.
  *
- * Returns 0 on success or -1 in case of error
+ * Returns non-negative device number on success or -1 in case of error
  */
-static int getFreeVethName(char *veth, int maxLen, int startDev)
+static int getFreeVethName(char **veth, int startDev)
 {
-    int rc = -1;
     int devNum = startDev-1;
-    char path[PATH_MAX];
+    char *path = NULL;

     do {
+        VIR_FREE(path);
         ++devNum;
-        snprintf(path, PATH_MAX, "/sys/class/net/veth%d/", devNum);
+        if (virAsprintf(&path, "/sys/class/net/veth%d/", devNum) < 0) {
+            virReportOOMError();
+            return -1;
+        }
     } while (virFileExists(path));
+    VIR_FREE(path);

-    snprintf(veth, maxLen, "veth%d", devNum);
-
-    rc = devNum;
-
-    return rc;
+    if (virAsprintf(veth, "veth%d", devNum) < 0) {
+        virReportOOMError();
+        return -1;
+    }
+    return devNum;
 }

 /**
  * vethCreate:
- * @veth1: name for one end of veth pair
- * @veth1MaxLen: max length of veth1 name
- * @veth2: name for one end of veth pair
- * @veth2MaxLen: max length of veth1 name
+ * @veth1: pointer to name for parent end of veth pair
+ * @veth2: pointer to return name for container end of veth pair
  *
  * Creates a veth device pair using the ip command:
  * ip link add veth1 type veth peer name veth2
+ * If veth1 points to NULL on entry, it will be a valid interface on
+ * return.  veth2 should point to NULL on entry.
+ *
  * NOTE: If veth1 and veth2 names are not specified, ip will auto assign
  *       names.  There seems to be two problems here -
  *       1) There doesn't seem to be a way to determine the names of the
@@ -78,43 +83,56 @@ static int getFreeVethName(char *veth, int maxLen, int startDev)
  *       2) Once one of the veth devices is moved to another namespace, it
  *          is no longer visible in the parent namespace.  This seems to
  *          confuse the name assignment causing it to fail with File exists.
- *       Because of these issues, this function currently forces the caller
- *       to fully specify the veth device names.
+ *       Because of these issues, this function currently allocates names
+ *       prior to using the ip command, and returns any allocated names
+ *       to the caller.
  *
  * Returns 0 on success or -1 in case of error
  */
-int vethCreate(char* veth1, int veth1MaxLen,
-               char* veth2, int veth2MaxLen)
+int vethCreate(char** veth1, char** veth2)
 {
     int rc;
     const char *argv[] = {
-        "ip", "link", "add", veth1, "type", "veth", "peer", "name", veth2, NULL
+        "ip", "link", "add", NULL, "type", "veth", "peer", "name", NULL, NULL
     };
     int cmdResult = 0;
     int vethDev = 0;
+    bool veth1_alloc = false;

-    DEBUG("veth1: %s veth2: %s", veth1, veth2);
+    DEBUG("veth1: %s veth2: %s", NULLSTR(*veth1), NULLSTR(*veth2));

-    while ((1 > strlen(veth1)) || STREQ(veth1, veth2)) {
-        vethDev = getFreeVethName(veth1, veth1MaxLen, 0);
-        ++vethDev;
-        DEBUG("Assigned veth1: %s", veth1);
+    if (*veth1 == NULL) {
+        vethDev = getFreeVethName(veth1, vethDev);
+        if (vethDev < 0)
+            return vethDev;
+        DEBUG("Assigned veth1: %s", *veth1);
+        veth1_alloc = true;
     }
-
-    while ((1 > strlen(veth2)) || STREQ(veth1, veth2)) {
-        vethDev = getFreeVethName(veth2, veth2MaxLen, vethDev);
-        ++vethDev;
-        DEBUG("Assigned veth2: %s", veth2);
+    argv[3] = *veth1;
+
+    while (*veth2 == NULL || STREQ(*veth1, *veth2)) {
+        VIR_FREE(*veth2);
+        vethDev = getFreeVethName(veth2, vethDev + 1);
+        if (vethDev < 0) {
+            if (veth1_alloc)
+                VIR_FREE(*veth1);
+            return vethDev;
+        }
+        DEBUG("Assigned veth2: %s", *veth2);
     }
+    argv[8] = *veth2;

-    DEBUG("veth1: %s veth2: %s", veth1, veth2);
+    DEBUG("veth1: %s veth2: %s", *veth1, *veth2);
     rc = virRun(argv, &cmdResult);

     if (rc != 0 ||
         (WIFEXITED(cmdResult) && WEXITSTATUS(cmdResult) != 0)) {
         vethError(VIR_ERR_INTERNAL_ERROR,
                   _("Failed to create veth device pair '%s', '%s': %d"),
-                  veth1, veth2, WEXITSTATUS(cmdResult));
+                  *veth1, *veth2, WEXITSTATUS(cmdResult));
+        if (veth1_alloc)
+            VIR_FREE(*veth1);
+        VIR_FREE(*veth2);
         rc = -1;
     }

diff --git a/src/lxc/veth.h b/src/lxc/veth.h
index 1ec1ec8..f50a939 100644
--- a/src/lxc/veth.h
+++ b/src/lxc/veth.h
@@ -1,6 +1,7 @@
 /*
  * veth.h: Interface to tools for managing veth pairs
  *
+ * Copyright (C) 2010 Red Hat, Inc.
  * Copyright IBM Corp. 2008
  *
  * See COPYING.LIB for the License of this software
@@ -16,9 +17,8 @@
 # include "internal.h"

 /* Function declarations */
-int vethCreate(char* veth1, int veth1MaxLen, char* veth2,
-               int veth2MaxLen)
-    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(3);
+int vethCreate(char** veth1, char** veth2)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
 int vethDelete(const char* veth)
     ATTRIBUTE_NONNULL(1);
 int vethInterfaceUpOrDown(const char* veth, int upOrDown)
-- 
1.7.2.2


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