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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.

(Sigh. I had visited this exact piece of the code due to an error during getnameinfo, and thought that setting network->len was the only thing missing.)

I think this is the right place to fix it; A caller to virSocketAddrMaskByPrefix (or virSocketAddrMask) shouldn't need to initialize the virSocketAddr (I think it really should be an opaque type outside of network.c, although it isn't always treated that way, even by me).

ACK.

  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.


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