Re: [Qemu-devel] [PATCH v4 2/5] 9p: Treat multiple devices on one export as an error

[Greg Kurz]

On Wed, 26 Jun 2019 20:30:41 +0200
Christian Schoenebeck via Qemu-devel <address@hidden> wrote:

> 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/wile/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 <address@hidden>

You should mention here the changes you made to the original patch.

> Signed-off-by: Christian Schoenebeck <address@hidden>
> ---
>  hw/9pfs/9p.c | 71 
> ++++++++++++++++++++++++++++++++++++++++++++++++------------
>  hw/9pfs/9p.h |  1 +
>  2 files changed, 58 insertions(+), 14 deletions(-)
> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index 586a6dccba..cbaa212625 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -572,10 +572,20 @@ 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) {
> +        pdu->s->dev_id = stbuf->st_dev;

st_dev should be captured in v9fs_device_realize_common() since we
lstat() the root there, instead of every request doing the check.

> +    } else if (pdu->s->dev_id != stbuf->st_dev) {
> +        error_report_once(
> +            "9p: Multiple devices detected in same VirtFS export. "
> +            "You must use a separate export for each device."
> +        );
> +        return -ENOSYS;

This error is likely to end up as the return value of a
syscall in the guest and -ENOSYS usually means the syscall
isn't implemented, which is obviously not the case. Maybe
return -EPERM instead ?

> +    }
> +
>      memset(&qidp->path, 0, sizeof(qidp->path));
>      size = MIN(sizeof(stbuf->st_ino), sizeof(qidp->path));
>      memcpy(&qidp->path, &stbuf->st_ino, size);
> @@ -587,6 +597,8 @@ 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,
> @@ -599,7 +611,10 @@ 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;
>  }
>  
> @@ -830,7 +845,10 @@ 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;
> @@ -891,7 +909,7 @@ 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));
> @@ -913,7 +931,7 @@ 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)
> @@ -1115,7 +1133,6 @@ 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) {
> @@ -1136,7 +1153,10 @@ 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) {
> @@ -1381,7 +1401,10 @@ 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));
> @@ -1483,7 +1506,10 @@ 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) {
> @@ -1593,7 +1619,10 @@ 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;
> @@ -2327,7 +2356,10 @@ 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;
> @@ -2384,7 +2416,10 @@ 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;
> @@ -3064,7 +3099,10 @@ 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;
> @@ -3222,7 +3260,10 @@ 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;
> @@ -3633,6 +3674,8 @@ int v9fs_device_realize_common(V9fsState *s, const 
> V9fsTransport *t,
>          goto out;
>      }
>  
> +    s->dev_id = 0;
> +

Set it to stat->st_dev after lstat() was called later in this function.

>      s->ctx.fst = &fse->fst;
>      fsdev_throttle_init(s->ctx.fst);
>  
> diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
> index 8883761b2c..5e316178d5 100644
> --- a/hw/9pfs/9p.h
> +++ b/hw/9pfs/9p.h
> @@ -256,6 +256,7 @@ struct V9fsState
>      Error *migration_blocker;
>      V9fsConf fsconf;
>      V9fsQID root_qid;
> +    dev_t dev_id;
>  };
>  
>  /* 9p2000.L open flags */