Re: [PATCH] lxc: fix lxcContainerMountAllFS() DEREF_BEFORE_CHECK

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On Thu, Sep 07, 2023 at 09:25:14AM +0200, Peter Krempa wrote:
On Thu, Sep 07, 2023 at 09:11:34 +0200, Martin Kletzander wrote:
On Wed, Sep 06, 2023 at 06:34:42PM +0300, Dmitry Frolov wrote:
> Reviewing the sources, I found, that
> in function lxcContainerMountAllFS() pointers
> vmDef->fss[i]->src and vmDef->fss[i]->src->path
> are checked for NULL after dereferencing in
> VIR_DEBUG() macro.
>
> Fixes: 57487085dc ("lxc: don't try to reference NULL when mounting filesystems")
> ---
> src/lxc/lxc_container.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)

[...]

>         if (lxcContainerResolveSymlinks(vmDef->fss[i], false) < 0)
>             return -1;
>
> -        if (!(vmDef->fss[i]->src && vmDef->fss[i]->src->path &&
> -              STRPREFIX(vmDef->fss[i]->src->path, vmDef->fss[i]->dst)) &&
> +        if (!STRPREFIX(vmDef->fss[i]->src->path, vmDef->fss[i]->dst) &&
>             lxcContainerUnmountSubtree(vmDef->fss[i]->dst, false) < 0)

... here it only skips the unmount in such case.  That makes sense
because for example tmpfs does not have a source path, only the
destination and the mount that is not visible in the context here would
not only be skipped as well, but the whole starting of a domain would
fail.

Instead of this patch, you could just conditionally change the
VIR_DEBUG() to report what's actually happening.

And we have a handy NULLSTR() macro for that case.


NULLSTR(a->b) won't help you if a == NULL, unfortunately :(



>             return -1;
>
> --
> 2.34.1
>


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