In fact, the 'tapfd' is always NULL, the function 'virNetDevTapCreate()' hasn't assign 'fd' to 'tapfd', when the function 'virNetDevSetMAC()' is failed then goto 'error' lable, finally, the VIR_FORCE_CLOSE() will deref a NULL 'tapfd'. * util/virnetdevtap.c (virNetDevTapCreateInBridgePort): fix a NULL pointer derefing. * How to reproduce? $ cat > /tmp/net.xml <<EOF <network> <name>test</name> <forward mode='nat'/> <bridge name='br1' stp='off' delay='1' /> <mac address='00:00:00:00:00:00'/> <ip address='192.168.100.1' netmask='255.255.255.0'> <dhcp> <range start='192.168.100.2' end='192.168.100.254' /> </dhcp> </ip> </network> EOF $ virsh net-define /tmp/net.xml $ virsh net-start test error: Failed to start network brTest error: End of file while reading data: Input/output error Signed-off-by: Alex Jia <ajia(a)redhat.com&gt; --- src/util/virnetdevtap.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/src/util/virnetdevtap.c b/src/util/virnetdevtap.c index 0b3ac46..5d21164 100644 --- a/src/util/virnetdevtap.c +++ b/src/util/virnetdevtap.c @@ -341,7 +341,8 @@ int virNetDevTapCreateInBridgePort(const char *brname, return 0; error: - VIR_FORCE_CLOSE(*tapfd); + if (tapfd) + VIR_FORCE_CLOSE(*tapfd); return errno; } -- 1.7.1