mirror of
https://gitlab.com/libvirt/libvirt.git
synced 2025-02-08 04:31:33 +00:00
ba2b5b7dbf
So, recently I was testing the LXC driver. You know, startup some
domains. But to my surprise, I was not able to start a single one:
virsh # start --console test
error: Reconnected to the hypervisor
error: Failed to start domain test
error: internal error: guest failed to start: unexpected exit status 125
So I've start digging. It turns out, that in virExec(), when I printed
out the @cmd, I got strange values: *(cmd->outfdptr) was certainly not
valid FD number: it has random value of several millions. This
obviously made prepareStdFd(childout, STDOUT_FILENO) fail (line 611).
But outfdptr is set in virCommandSetOutputFD(). The only place within
LXC driver where the function is called is in
virLXCProcessBuildControllerCmd(). If you take a closer look at the
function it looks like this:
static virCommandPtr
virLXCProcessBuildControllerCmd(virLXCDriverPtr driver,
..
int logfd,
const char *pidfile)
{
...
virCommandSetOutputFD(cmd, &logfd);
virCommandSetErrorFD(cmd, &logfd);
...
}
Yes, you guessed it. @logfd is passed into the function by value.
However, in the function we try to get its address (an address of a
local variable) which is no longer valid once function is finished and
stack is cleaned. Therefore when cmd->outfdptr is evaluated at any
point after this function, we may get a random number, depending on
what's currently on the stack. Of course, this may work sometimes too
- it depends on the compiler how it arranges the code, when the stack
is wiped out.
In order to fix this, lets pass a pointer to @logfd instead of
figuring out (wrong) its value in a function.
The bug was introduced in e1de5521.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
(cherry picked from commit 302146b16d204e3feb8f04a9f81b8f587c827302)
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>