Re: [Qemu-stable] [PATCH] 9pfs: fix potential segfault during walk

[Greg Kurz]

On Fri, 16 Sep 2016 01:05:11 +0200
Greg Kurz <address@hidden> wrote:

> If the call to fid_to_qid() returns an error, we will call v9fs_path_free()
> on uninitialized paths.
> 

I'll add this to the changelog:

It is a regression introduced by the following commit:

56f101ecce0e 9pfs: handle walk of ".." in the root directory

> Let's fix this by initializing dpath and path before calling fid_to_qid().
> 
> Signed-off-by: Greg Kurz <address@hidden>
> ---
> 
> Thanks Paolo (and Coverity) for spotting this.
> 
> Cc'ing stable as this is a regression introduced in 2.7. It is also present
> in Michael's stable-2.6-staging branch.
> 
>  hw/9pfs/9p.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index dfe293d11d1c..91a497079acb 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -1320,13 +1320,14 @@ static void v9fs_walk(void *opaque)
>          goto out_nofid;
>      }
>  
> +    v9fs_path_init(&dpath);
> +    v9fs_path_init(&path);
> +
>      err = fid_to_qid(pdu, fidp, &qid);
>      if (err < 0) {
>          goto out;
>      }
>  
> -    v9fs_path_init(&dpath);
> -    v9fs_path_init(&path);
>      /*
>       * Both dpath and path initially poin to fidp.
>       * Needed to handle request with nwnames == 0
>