Re: [Qemu-devel] [PATCH v3 1/3] 9pfs: forbid illegal path names

[Greg Kurz]

I forgot to pass --edit-patches to stg mail and some mails managed to get
away before I hit ^C :\

Please ignore this thread:

<address@hidden>

and look at this one instead:

<address@hidden>

Sorry for the noise.

On Tue, 30 Aug 2016 16:59:52 +0200
Greg Kurz <address@hidden> wrote:

> Empty path components don't make sense for most commands and may cause
> undefined behavior, depending on the backend. A notable exception
> would be the target of a symbolic link: POSIX requires implementations
> to support the empty string for target names. But 9p is only supported
> on linux hosts, which don't support empty target names yet, and the
> proposal to error out with ENOENT got approved, as indicated here:
> 
>       http://austingroupbugs.net/view.php?id=649
> 
> For the sake of consistency and simplicity, symlink target names will be
> treated the same as any other file name argument.
> 
> Also, the walk request described in the 9P spec [1] clearly shows that
> the client is supposed to send individual path components: the official
> linux client never sends portions of path containing the / character for
> example.
> 
> Moreover, the 9P spec [2] also states that a system can decide to restrict
> the set of supported characters used in path components, with an explicit
> mention "to remove slashes from name components".
> 
> This patch introduces a new name_is_illegal() helper that checks the
> names sent by the client are not empty and don't contain unwanted chars.
> Since 9pfs is only supported on linux hosts, only the / character is
> checked at the moment. When support for other hosts (AKA. win32) is added,
> other chars may need to be blacklisted as well.
> 
> If a client sends an illegal path component, the request will fail and
> ENOENT is returned to the client.
> 
> [1] http://man.cat-v.org/plan_9/5/walk
> [2] http://man.cat-v.org/plan_9/5/intro
> 
> Suggested-by: Peter Maydell <address@hidden>
> Signed-off-by: Greg Kurz <address@hidden>
> 
> v3: - fix empty string check in name_is_illegal()
>     - return ENOENT instead of EINVAL
>     - added checking of target names for symlinks in create (9P2000.u)
>     - added some details about symlink target names in the changelog
> ---
>  hw/9pfs/9p.c |   61 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index b6b02b46a9da..fe2d27f12ae1 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -1256,6 +1256,11 @@ static int v9fs_walk_marshal(V9fsPDU *pdu, uint16_t 
> nwnames, V9fsQID *qids)
>      return offset;
>  }
>  
> +static bool name_is_illegal(const char *name)
> +{
> +    return !*name || strchr(name, '/') != NULL;
> +}
> +
>  static void v9fs_walk(void *opaque)
>  {
>      int name_idx;
> @@ -1289,6 +1294,10 @@ static void v9fs_walk(void *opaque)
>              if (err < 0) {
>                  goto out_nofid;
>              }
> +            if (name_is_illegal(wnames[i].data)) {
> +                err = -ENOENT;
> +                goto out_nofid;
> +            }
>              offset += err;
>          }
>      } else if (nwnames > P9_MAXWELEM) {
> @@ -1483,6 +1492,11 @@ static void v9fs_lcreate(void *opaque)
>      }
>      trace_v9fs_lcreate(pdu->tag, pdu->id, dfid, flags, mode, gid);
>  
> +    if (name_is_illegal(name.data)) {
> +        err = -ENOENT;
> +        goto out_nofid;
> +    }
> +
>      fidp = get_fid(pdu, dfid);
>      if (fidp == NULL) {
>          err = -ENOENT;
> @@ -2077,6 +2091,11 @@ static void v9fs_create(void *opaque)
>      }
>      trace_v9fs_create(pdu->tag, pdu->id, fid, name.data, perm, mode);
>  
> +    if (name_is_illegal(name.data)) {
> +        err = -ENOENT;
> +        goto out_nofid;
> +    }
> +
>      fidp = get_fid(pdu, fid);
>      if (fidp == NULL) {
>          err = -EINVAL;
> @@ -2099,6 +2118,11 @@ static void v9fs_create(void *opaque)
>          }
>          fidp->fid_type = P9_FID_DIR;
>      } else if (perm & P9_STAT_MODE_SYMLINK) {
> +        if (name_is_illegal(extension.data)) {
> +            err = -ENOENT;
> +            goto out_nofid;
> +        }
> +
>          err = v9fs_co_symlink(pdu, fidp, &name,
>                                extension.data, -1 , &stbuf);
>          if (err < 0) {
> @@ -2242,6 +2266,11 @@ static void v9fs_symlink(void *opaque)
>      }
>      trace_v9fs_symlink(pdu->tag, pdu->id, dfid, name.data, symname.data, 
> gid);
>  
> +    if (name_is_illegal(name.data) || name_is_illegal(symname.data)) {
> +        err = -ENOENT;
> +        goto out_nofid;
> +    }
> +
>      dfidp = get_fid(pdu, dfid);
>      if (dfidp == NULL) {
>          err = -EINVAL;
> @@ -2316,6 +2345,11 @@ static void v9fs_link(void *opaque)
>      }
>      trace_v9fs_link(pdu->tag, pdu->id, dfid, oldfid, name.data);
>  
> +    if (name_is_illegal(name.data)) {
> +        err = -ENOENT;
> +        goto out_nofid;
> +    }
> +
>      dfidp = get_fid(pdu, dfid);
>      if (dfidp == NULL) {
>          err = -ENOENT;
> @@ -2398,6 +2432,12 @@ static void v9fs_unlinkat(void *opaque)
>      if (err < 0) {
>          goto out_nofid;
>      }
> +
> +    if (name_is_illegal(name.data)) {
> +        err = -ENOENT;
> +        goto out_nofid;
> +    }
> +
>      dfidp = get_fid(pdu, dfid);
>      if (dfidp == NULL) {
>          err = -EINVAL;
> @@ -2504,6 +2544,12 @@ static void v9fs_rename(void *opaque)
>      if (err < 0) {
>          goto out_nofid;
>      }
> +
> +    if (name_is_illegal(name.data)) {
> +        err = -ENOENT;
> +        goto out_nofid;
> +    }
> +
>      fidp = get_fid(pdu, fid);
>      if (fidp == NULL) {
>          err = -ENOENT;
> @@ -2616,6 +2662,11 @@ static void v9fs_renameat(void *opaque)
>          goto out_err;
>      }
>  
> +    if (name_is_illegal(old_name.data) || name_is_illegal(new_name.data)) {
> +        err = -ENOENT;
> +        goto out_err;
> +    }
> +
>      v9fs_path_write_lock(s);
>      err = v9fs_complete_renameat(pdu, olddirfid,
>                                   &old_name, newdirfid, &new_name);
> @@ -2826,6 +2877,11 @@ static void v9fs_mknod(void *opaque)
>      }
>      trace_v9fs_mknod(pdu->tag, pdu->id, fid, mode, major, minor);
>  
> +    if (name_is_illegal(name.data)) {
> +        err = -ENOENT;
> +        goto out_nofid;
> +    }
> +
>      fidp = get_fid(pdu, fid);
>      if (fidp == NULL) {
>          err = -ENOENT;
> @@ -2977,6 +3033,11 @@ static void v9fs_mkdir(void *opaque)
>      }
>      trace_v9fs_mkdir(pdu->tag, pdu->id, fid, name.data, mode, gid);
>  
> +    if (name_is_illegal(name.data)) {
> +        err = -ENOENT;
> +        goto out_nofid;
> +    }
> +
>      fidp = get_fid(pdu, fid);
>      if (fidp == NULL) {
>          err = -ENOENT;
> 
>