Re: [PATCH 2/3] 9pfs: capture root stat

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

On Donnerstag, 27. Mai 2021 19:04:11 CEST Christian Schoenebeck wrote:
> We already capture the QID of the exported 9p root path, i.e. to
> prevent client access outside the defined, exported filesystem's tree.
> This is currently checked by comparing the root QID with another FID's
> QID.
> 
> The problem with the latter is that resolving a QID of any given 9p path
> can only be done on 9p server's main thread, that's because it might
> mutate the server's state if inode remapping is enabled.
> 
> For that reason also capture the POSIX stat info of the root path for
> being able to identify on any (e.g. worker) thread whether an
> arbitrary given path is identical to the export root.
> 
> Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> ---
>  hw/9pfs/9p.c | 10 +++++++++-
>  hw/9pfs/9p.h |  1 +
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index 89aa07db78..825de1561d 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -1400,6 +1400,7 @@ static void coroutine_fn v9fs_attach(void *opaque)
>      size_t offset = 7;
>      V9fsQID qid;
>      ssize_t err;
> +    struct stat stbuf;
> 
>      v9fs_string_init(&uname);
>      v9fs_string_init(&aname);
> @@ -1422,7 +1423,13 @@ static void coroutine_fn v9fs_attach(void *opaque)
>          clunk_fid(s, fid);
>          goto out;
>      }
> -    err = fid_to_qid(pdu, fidp, &qid);
> +    err = v9fs_co_lstat(pdu, &fidp->path, &stbuf);
> +    if (err < 0) {
> +        err = -EINVAL;
> +        clunk_fid(s, fid);
> +        goto out;
> +    }
> +    err = stat_to_qid(pdu, &stbuf, &qid);
>      if (err < 0) {
>          err = -EINVAL;
>          clunk_fid(s, fid);
> @@ -1455,6 +1462,7 @@ static void coroutine_fn v9fs_attach(void *opaque)
>      err += offset;
> 
>      memcpy(&s->root_qid, &qid, sizeof(qid));
> +    memcpy(&s->root_st, &stbuf, sizeof(struct stat));

I'll make that sizeof(stbuf) instead to match with common code style here.

>      trace_v9fs_attach_return(pdu->tag, pdu->id,
>                               qid.type, qid.version, qid.path);
>  out:
> diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
> index 00381591ff..6f0b4c78c0 100644
> --- a/hw/9pfs/9p.h
> +++ b/hw/9pfs/9p.h
> @@ -356,6 +356,7 @@ struct V9fsState {
>      Error *migration_blocker;
>      V9fsConf fsconf;
>      V9fsQID root_qid;
> +    struct stat root_st;
>      dev_t dev_id;
>      struct qht qpd_table;
>      struct qht qpp_table;