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Re: [libvirt] [PATCH] qemu: avoid pass null pointer as an argument



On 08/04/2011 09:31 AM, Alex Jia wrote:
In fact, 'pos' is always -1, this reason is because qemuProcessStart function
assigns -1 to 'pos' variable then call qemuProcessWaitForMonitor,

Actually, qemuProcessStart always calls qemuProcessWaitForMonitor with non-negative pos (pos was set by lseek()ing to the end of the log file).

> meanwhile,
qemuProcessAttach function also call qemuProcessWaitForMonitor and directly
pass -1 as an argument, so if (pos != -1) statement can't been run for ever,

Rather, this merely means that the if (pos != -1) statement wasn't run when called by qemuProcessAttach.

it also means we can't allocate memory to 'buf' variable, that is, 'buf' is
a initial value NULL, however, the function
qemuProcessReadLogFD(logfd, buf, buf_size, strlen(buf)) will be called
on 'cleanup' section, null pointer passed as an argument.

* src/qemu/qemu_process.c: avoid null pointer passed as an argument to a
  'nonnull' parameter.

We definitely have a bug here, but this is not the right fix. The bug is that the cleanup: label is trying to read from logfd if the vm crashed, without having opened logfd in the qemuProcessAttach case.

I think the more appropriate patch is this:

diff --git i/src/qemu/qemu_process.c w/src/qemu/qemu_process.c
index 8508ff6..1eea45f 100644
--- i/src/qemu/qemu_process.c
+++ w/src/qemu/qemu_process.c
@@ -1214,7 +1214,7 @@ qemuProcessWaitForMonitor(struct qemud_driver* driver,
 cleanup:
     virHashFree(paths);

-    if (kill(vm->pid, 0) == -1 && errno == ESRCH) {
+    if (pos != -1 && kill(vm->pid, 0) == -1 && errno == ESRCH) {
         /* VM is dead, any other error raised in the interim is probably
          * not as important as the qemu cmdline output */
         qemuProcessReadLogFD(logfd, buf, buf_size, strlen(buf));

--
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org


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