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Re: [libvirt] [PATCH] qemu_driver: avoid NULL dereference



On Mon, May 17, 2010 at 01:04:24PM +0200, Jim Meyering wrote:
> The following theoretical possibility of a NULL dereference
> has been in the code since April 1
> (commit 6e41f30efcac08e50b21d9c943d6d27e90555951).
> It's theoretical, because if that vm = NULL
> statement is ever executed, the very next one,
> calling virDomainObjUnlock would dereference that now-NULL "vm".
> Hence, I think we can conclude the vm = NULL statement is
> effectively dead code.  That conclusion is in line with the
> "should" in the preceding comment.

> 
> 
> >From f88969b986a1c88985671c9d6fa9cb1dc449ed74 Mon Sep 17 00:00:00 2001
> From: Jim Meyering <meyering redhat com>
> Date: Mon, 17 May 2010 12:10:52 +0200
> Subject: [PATCH] qemu_driver: avoid NULL dereference
> 
> * src/qemu/qemu_driver.c (qemudDomainStart): After setting vm to NULL,
> goto cleanup, rather than dereferencing the NULL pointer.
> ---
>  src/qemu/qemu_driver.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 8f69b5a..3559e36 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -6489,8 +6489,11 @@ static int qemudDomainStart(virDomainPtr dom) {
>           * We should still have a reference left to vm but
>           * one should check for 0 anyway
>           */
> -        if (qemuDomainObjEndJob(vm) == 0)
> +        if (qemuDomainObjEndJob(vm) = 0) {
>              vm = NULL;
> +            goto cleanup;
> +        }
> +
>          virDomainObjUnlock(vm);
>          qemuDriverUnlock(driver);
>          ret = qemudDomainRestore(dom->conn, managed_save);

ACK


Daniel
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