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Re: [libvirt] [PATCH] network: plug unininitialized read found by valgrind



On 01/10/2011 05:28 PM, Eric Blake wrote:
* src/util/network.c (virSocketAddrMask): Zero out port, so that
iptables can initialize just the netmask, then call
virSocketFormatAddr without an uninitialized read in getnameinfo.
---

I'm not sure if this is the best patch; an alternative would be
to call memset(network,0,sizeof network) in iptablesFormatNetwork
prior to virSocketAddrMaskByPrefix.  But with this patch in place,
valgrind no longer complained about:

==31478== Use of uninitialised value of size 8
==31478==    at 0x3021643DAB: _itoa_word (in /lib64/libc-2.12.so)
==31478==    by 0x3021644E74: vfprintf (in /lib64/libc-2.12.so)
==31478==    by 0x302166EFB1: vsnprintf (in /lib64/libc-2.12.so)
==31478==    by 0x302164F022: snprintf (in /lib64/libc-2.12.so)
==31478==    by 0x3021705135: getnameinfo (in /lib64/libc-2.12.so)
==31478==    by 0x4E4FE00: virSocketFormatAddrFull (network.c:194)
==31478==    by 0x4E4FCAE: virSocketFormatAddr (network.c:152)
==31478==    by 0x4E43688: iptablesFormatNetwork (iptables.c:307)
==31478==    by 0x4E43FDE: iptablesForwardMasquerade (iptables.c:761)
==31478==    by 0x4E44392: iptablesRemoveForwardMasquerade (iptables.c:863)
==31478==    by 0x4A8BEF: networkRemoveMasqueradingIptablesRules (bridge_driver.c:893)
==31478==    by 0x4A9BCA: networkRemoveIpSpecificIptablesRules (bridge_driver.c:1244)
==31478==  Uninitialised value was created by a stack allocation
==31478==    at 0x4E43570: iptablesFormatNetwork (iptables.c:289)

So I'm assuming that the uninitialized read was due to gethostname
looking at the port field which was still filled with uninitialized
stack data.

  src/util/network.c |    6 +++++-
  1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/src/util/network.c b/src/util/network.c
index a7e7423..33028aa 100644
--- a/src/util/network.c
+++ b/src/util/network.c
@@ -1,7 +1,7 @@
  /*
   * network.c: network helper APIs for libvirt
   *
- * Copyright (C) 2009-2010 Red Hat, Inc.
+ * Copyright (C) 2009-2011 Red Hat, Inc.
   *
   * See COPYING.LIB for the License of this software
   *
@@ -291,6 +291,7 @@ int virSocketAddrIsNetmask(virSocketAddrPtr netmask) {
   * virSocketAddrMask:
   * @addr: address that needs to be masked
   * @netmask: the netmask address
+ * @network: where to store the result, can be same as @addr
   *
   * Mask off the host bits of @addr according to @netmask, turning it
   * into a network address.
@@ -311,6 +312,7 @@ virSocketAddrMask(const virSocketAddrPtr addr,
          network->data.inet4.sin_addr.s_addr
              = (addr->data.inet4.sin_addr.s_addr
                 &  netmask->data.inet4.sin_addr.s_addr);
+        network->data.inet4.sin_port = 0;
          network->data.stor.ss_family = AF_INET;
          network->len = addr->len;
          return 0;
@@ -322,6 +324,7 @@ virSocketAddrMask(const virSocketAddrPtr addr,
                  = (addr->data.inet6.sin6_addr.s6_addr[ii]
                     &  netmask->data.inet6.sin6_addr.s6_addr[ii]);
          }
+        network->data.inet6.sin6_port = 0;
          network->data.stor.ss_family = AF_INET6;
          network->len = addr->len;
          return 0;
@@ -334,6 +337,7 @@ virSocketAddrMask(const virSocketAddrPtr addr,
   * virSocketAddrMaskByPrefix:
   * @addr: address that needs to be masked
   * @prefix: prefix (# of 1 bits) of netmask to apply
+ * @network: where to store the result, can be same as @addr
   *
   * Mask off the host bits of @addr according to @prefix, turning it
   * into a network address.
ACK.

   Stefan


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