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Cause: bug in the error handling code of vhost, check whether an unsigned value is greater than zero would make the result always true.
Consequence: qemu-kvm would hang when it met errors when start a vhost_net backend.
Fix: Fix the error handling code.
Result: qemu-kvm would never hang when it fails to start vhost_net backend.
Description of problem:
hw/vhost_net.c:vhost_net_start() seems to have untested error handling.
The code looks like this:
int vhost_net_start(struct vhost_net *net,
VirtIODevice *dev)
{
struct vhost_vring_file file = { };
...
for (file.index = 0; file.index < net->dev.nvqs; ++file.index) {
r = ioctl(net->dev.control, VHOST_NET_SET_BACKEND, &file);
if (r < 0) {
r = -errno;
goto fail;
}
}
return 0;
fail:
file.fd = -1;
while (--file.index >= 0) {
int r = ioctl(net->dev.control, VHOST_NET_SET_BACKEND, &file);
assert(r >= 0);
}
As file.index is an unsigned integer, the while() loop will
always be true, so in case of error we will exit on an assert
or loop forever.
This is present in both RHEL6 and upstream QEMU.
It is not obvious to me what the code was intended to do here,
so please have a look.
Version-Release number of selected component (if applicable):
How reproducible:
Steps to Reproduce:
1.
2.
3.
Actual results:
Expected results:
Additional info:
Technical note added. If any revisions are required, please edit the "Technical Notes" field
accordingly. All revisions will be proofread by the Engineering Content Services team.
New Contents:
Cause: bug in the error handling code of vhost, check whether an unsigned value is greater than zero would make the result always true.
Consequence: qemu-kvm would hang when it met errors when start a vhost_net backend.
Fix: Fix the error handling code.
Result: qemu-kvm would never hang when it fails to start vhost_net backend.
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.
http://rhn.redhat.com/errata/RHSA-2011-0534.html
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.
http://rhn.redhat.com/errata/RHSA-2011-0534.html
Description of problem: hw/vhost_net.c:vhost_net_start() seems to have untested error handling. The code looks like this: int vhost_net_start(struct vhost_net *net, VirtIODevice *dev) { struct vhost_vring_file file = { }; ... for (file.index = 0; file.index < net->dev.nvqs; ++file.index) { r = ioctl(net->dev.control, VHOST_NET_SET_BACKEND, &file); if (r < 0) { r = -errno; goto fail; } } return 0; fail: file.fd = -1; while (--file.index >= 0) { int r = ioctl(net->dev.control, VHOST_NET_SET_BACKEND, &file); assert(r >= 0); } As file.index is an unsigned integer, the while() loop will always be true, so in case of error we will exit on an assert or loop forever. This is present in both RHEL6 and upstream QEMU. It is not obvious to me what the code was intended to do here, so please have a look. Version-Release number of selected component (if applicable): How reproducible: Steps to Reproduce: 1. 2. 3. Actual results: Expected results: Additional info: