9p: fix fid refcount leak in v9fs_vfs_get_link

we check for protocol version later than required, after a fid has
been obtained. Just move the version check earlier.

Link: https://lkml.kernel.org/r/20220612085330.1451496-3-asmadeus@codewreck.org
Fixes: 6636b6dcc3db ("9p: add refcount to p9_fid struct")
Cc: stable@vger.kernel.org
Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>

diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 419d2f3..3d82977 100644 (file)
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -1251,15 +1251,15 @@ static const char *v9fs_vfs_get_link(struct dentry *dentry,
                return ERR_PTR(-ECHILD);
 
        v9ses = v9fs_dentry2v9ses(dentry);
-       fid = v9fs_fid_lookup(dentry);
+       if (!v9fs_proto_dotu(v9ses))
+               return ERR_PTR(-EBADF);
+
        p9_debug(P9_DEBUG_VFS, "%pd\n", dentry);
+       fid = v9fs_fid_lookup(dentry);
 
        if (IS_ERR(fid))
                return ERR_CAST(fid);
 
-       if (!v9fs_proto_dotu(v9ses))
-               return ERR_PTR(-EBADF);
-
        st = p9_client_stat(fid);
        p9_client_clunk(fid);
        if (IS_ERR(st))