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

[Christian Schoenebeck]

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));
     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;
-- 
2.20.1