Re: [Qemu-devel] [Virtio-fs] [PATCH 2/5] virtiofsd: prevent lo_lookup() NULL pointer dereference

[piaojun]

Hi Stefan,

On 2019/7/26 17:11, Stefan Hajnoczi wrote:
> Most lo_do_lookup() have already checked that the parent inode exists.
> lo_lookup() hasn't and can therefore hit a NULL pointer dereference when
> lo_inode(req, parent) returns NULL.
> 
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
>  contrib/virtiofsd/passthrough_ll.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/contrib/virtiofsd/passthrough_ll.c 
> b/contrib/virtiofsd/passthrough_ll.c
> index 9ae1381618..277a17fc03 100644
> --- a/contrib/virtiofsd/passthrough_ll.c
> +++ b/contrib/virtiofsd/passthrough_ll.c
> @@ -766,6 +766,10 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t 
> parent, const char *name,
>       struct lo_data *lo = lo_data(req);
>       struct lo_inode *inode, *dir = lo_inode(req, parent);
>  
> +     if (!dir) {
> +             return EBADF;
> +     }
> +

I worry about that dir will be released or set NULL just after NULL
checking. Or could we use some lock to prevent the simultaneity?

Thanks,
Jun

>       memset(e, 0, sizeof(*e));
>       e->attr_timeout = lo->timeout;
>       e->entry_timeout = lo->timeout;
>