Re: [Qemu-devel] [PATCH 2/4] 9pfs: check for file device to avoid QID path collisions

[Greg Kurz <groug@kaod.org>]

On Thu, 8 Feb 2018 19:00:17 +0100
<antonios.motakis@huawei.com> wrote:

> From: Antonios Motakis <antonios.motakis@huawei.com>
> 
> The QID path should uniquely identify a file. However, the
> inode of a file is currently used as the QID path, which
> on its own only uniquely identifies wiles within a device.
                                      ^^^^^
                                    s/wiles/files

> Here we track the device hosting the 9pfs share, in order
> to prevent security issues with QID path collisions from
> other devices.
> 
> Signed-off-by: Antonios Motakis <antonios.motakis@huawei.com>
> ---
>  hw/9pfs/9p.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++-------------
>  hw/9pfs/9p.h |  1 +
>  2 files changed, 54 insertions(+), 14 deletions(-)
> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index 85a1ed8..4da858f 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -573,10 +573,16 @@ static void coroutine_fn virtfs_reset(V9fsPDU *pdu)
>                                  P9_STAT_MODE_SOCKET)
>  
>  /* This is the algorithm from ufs in spfs */
> -static void stat_to_qid(const struct stat *stbuf, V9fsQID *qidp)
> +static int stat_to_qid(V9fsPDU *pdu, const struct stat *stbuf, V9fsQID *qidp)
>  {
>      size_t size;
>  
> +    if (pdu->s->dev_id == 0) {

This check would then be performed by nearly all
requests. I'd rather set stbuf->st_dev at realize
time since we lstat() the root of the 9pfs share.

> +        pdu->s->dev_id = stbuf->st_dev;
> +    } else if (pdu->s->dev_id != stbuf->st_dev) {
> +        return -ENOSYS;

Not sure ENOSYS is an appropriate return value for most guest
syscalls that would land here. Maybe ENOENT like if the path
doesn't exist instead ?

This being said, this st_dev related logic gets reverted in the
next patch IIUC... maybe this patch should just care to add a
return value to stat_to_qid() ?

> +    }
> +
>      memset(&qidp->path, 0, sizeof(qidp->path));
>      size = MIN(sizeof(stbuf->st_ino), sizeof(qidp->path));
>      memcpy(&qidp->path, &stbuf->st_ino, size);
> @@ -588,6 +594,8 @@ static void stat_to_qid(const struct stat *stbuf, V9fsQID *qidp)
>      if (S_ISLNK(stbuf->st_mode)) {
>          qidp->type |= P9_QID_TYPE_SYMLINK;
>      }
> +
> +    return 0;
>  }
>  
>  static int coroutine_fn fid_to_qid(V9fsPDU *pdu, V9fsFidState *fidp,
> @@ -600,7 +608,10 @@ static int coroutine_fn fid_to_qid(V9fsPDU *pdu, V9fsFidState *fidp,
>      if (err < 0) {
>          return err;
>      }
> -    stat_to_qid(&stbuf, qidp);
> +    err = stat_to_qid(pdu, &stbuf, qidp);
> +    if (err < 0) {
> +        return err;
> +    }
>      return 0;
>  }
>  
> @@ -831,7 +842,10 @@ static int coroutine_fn stat_to_v9stat(V9fsPDU *pdu, V9fsPath *path,
>  
>      memset(v9stat, 0, sizeof(*v9stat));
>  
> -    stat_to_qid(stbuf, &v9stat->qid);
> +    err = stat_to_qid(pdu, stbuf, &v9stat->qid);
> +    if (err < 0) {
> +        return err;
> +    }
>      v9stat->mode = stat_to_v9mode(stbuf);
>      v9stat->atime = stbuf->st_atime;
>      v9stat->mtime = stbuf->st_mtime;
> @@ -892,7 +906,7 @@ static int coroutine_fn stat_to_v9stat(V9fsPDU *pdu, V9fsPath *path,
>  #define P9_STATS_ALL           0x00003fffULL /* Mask for All fields above */
>  
>  
> -static void stat_to_v9stat_dotl(V9fsState *s, const struct stat *stbuf,
> +static int stat_to_v9stat_dotl(V9fsPDU *pdu, const struct stat *stbuf,
>                                  V9fsStatDotl *v9lstat)
>  {
>      memset(v9lstat, 0, sizeof(*v9lstat));
> @@ -914,7 +928,7 @@ static void stat_to_v9stat_dotl(V9fsState *s, const struct stat *stbuf,
>      /* Currently we only support BASIC fields in stat */
>      v9lstat->st_result_mask = P9_STATS_BASIC;
>  
> -    stat_to_qid(stbuf, &v9lstat->qid);
> +    return stat_to_qid(pdu, stbuf, &v9lstat->qid);
>  }
>  
>  static void print_sg(struct iovec *sg, int cnt)
> @@ -1116,7 +1130,6 @@ static void coroutine_fn v9fs_getattr(void *opaque)
>      uint64_t request_mask;
>      V9fsStatDotl v9stat_dotl;
>      V9fsPDU *pdu = opaque;
> -    V9fsState *s = pdu->s;
>  
>      retval = pdu_unmarshal(pdu, offset, "dq", &fid, &request_mask);
>      if (retval < 0) {
> @@ -1137,7 +1150,10 @@ static void coroutine_fn v9fs_getattr(void *opaque)
>      if (retval < 0) {
>          goto out;
>      }
> -    stat_to_v9stat_dotl(s, &stbuf, &v9stat_dotl);
> +    retval = stat_to_v9stat_dotl(pdu, &stbuf, &v9stat_dotl);
> +    if (retval < 0) {
> +        goto out;
> +    }
>  
>      /*  fill st_gen if requested and supported by underlying fs */
>      if (request_mask & P9_STATS_GEN) {
> @@ -1377,7 +1393,10 @@ static void coroutine_fn v9fs_walk(void *opaque)
>              if (err < 0) {
>                  goto out;
>              }
> -            stat_to_qid(&stbuf, &qid);
> +            err = stat_to_qid(pdu, &stbuf, &qid);
> +            if (err < 0) {
> +                goto out;
> +            }
>              v9fs_path_copy(&dpath, &path);
>          }
>          memcpy(&qids[name_idx], &qid, sizeof(qid));
> @@ -1477,7 +1496,10 @@ static void coroutine_fn v9fs_open(void *opaque)
>      if (err < 0) {
>          goto out;
>      }
> -    stat_to_qid(&stbuf, &qid);
> +    err = stat_to_qid(pdu, &stbuf, &qid);
> +    if (err < 0) {
> +        goto out;
> +    }
>      if (S_ISDIR(stbuf.st_mode)) {
>          err = v9fs_co_opendir(pdu, fidp);
>          if (err < 0) {
> @@ -1587,7 +1609,10 @@ static void coroutine_fn v9fs_lcreate(void *opaque)
>          fidp->flags |= FID_NON_RECLAIMABLE;
>      }
>      iounit =  get_iounit(pdu, &fidp->path);
> -    stat_to_qid(&stbuf, &qid);
> +    err = stat_to_qid(pdu, &stbuf, &qid);
> +    if (err < 0) {
> +        goto out;
> +    }
>      err = pdu_marshal(pdu, offset, "Qd", &qid, iounit);
>      if (err < 0) {
>          goto out;
> @@ -2308,7 +2333,10 @@ static void coroutine_fn v9fs_create(void *opaque)
>          }
>      }
>      iounit = get_iounit(pdu, &fidp->path);
> -    stat_to_qid(&stbuf, &qid);
> +    err = stat_to_qid(pdu, &stbuf, &qid);
> +    if (err < 0) {
> +        goto out;
> +    }
>      err = pdu_marshal(pdu, offset, "Qd", &qid, iounit);
>      if (err < 0) {
>          goto out;
> @@ -2365,7 +2393,10 @@ static void coroutine_fn v9fs_symlink(void *opaque)
>      if (err < 0) {
>          goto out;
>      }
> -    stat_to_qid(&stbuf, &qid);
> +    err = stat_to_qid(pdu, &stbuf, &qid);
> +    if (err < 0) {
> +        goto out;
> +    }
>      err =  pdu_marshal(pdu, offset, "Q", &qid);
>      if (err < 0) {
>          goto out;
> @@ -3033,7 +3064,10 @@ static void coroutine_fn v9fs_mknod(void *opaque)
>      if (err < 0) {
>          goto out;
>      }
> -    stat_to_qid(&stbuf, &qid);
> +    err = stat_to_qid(pdu, &stbuf, &qid);
> +    if (err < 0) {
> +        goto out;
> +    }
>      err = pdu_marshal(pdu, offset, "Q", &qid);
>      if (err < 0) {
>          goto out;
> @@ -3191,7 +3225,10 @@ static void coroutine_fn v9fs_mkdir(void *opaque)
>      if (err < 0) {
>          goto out;
>      }
> -    stat_to_qid(&stbuf, &qid);
> +    err = stat_to_qid(pdu, &stbuf, &qid);
> +    if (err < 0) {
> +        goto out;
> +    }
>      err = pdu_marshal(pdu, offset, "Q", &qid);
>      if (err < 0) {
>          goto out;
> @@ -3589,6 +3626,8 @@ int v9fs_device_realize_common(V9fsState *s, const V9fsTransport *t,
>          goto out;
>      }
>  
> +    s->dev_id = 0;
> +
>      s->ctx.fst = &fse->fst;
>      fsdev_throttle_init(s->ctx.fst);
>  
> diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
> index 5ced427..afb4ebd 100644
> --- a/hw/9pfs/9p.h
> +++ b/hw/9pfs/9p.h
> @@ -252,6 +252,7 @@ struct V9fsState
>      Error *migration_blocker;
>      V9fsConf fsconf;
>      V9fsQID root_qid;
> +    dev_t dev_id;
>  };
>  
>  /* 9p2000.L open flags */