9p: attach-per-user

The 9P2000 protocol requires the authentication and permission checks to be
done in the file server. For that reason every user that accesses the file
server tree has to authenticate and attach to the server separately.
Multiple users can share the same connection to the server.

Currently v9fs does a single attach and executes all I/O operations as a
single user. This makes using v9fs in multiuser environment unsafe as it
depends on the client doing the permission checking.

This patch improves the 9P2000 support by allowing every user to attach
separately. The patch defines three modes of access (new mount option
'access'):

- attach-per-user (access=user) (default mode for 9P2000.u)
 If a user tries to access a file served by v9fs for the first time, v9fs
 sends an attach command to the server (Tattach) specifying the user. If
 the attach succeeds, the user can access the v9fs tree.
 As there is no uname->uid (string->integer) mapping yet, this mode works
 only with the 9P2000.u dialect.

- allow only one user to access the tree (access=<uid>)
 Only the user with uid can access the v9fs tree. Other users that attempt
 to access it will get EPERM error.

- do all operations as a single user (access=any) (default for 9P2000)
 V9fs does a single attach and all operations are done as a single user.
 If this mode is selected, the v9fs behavior is identical with the current
 one.

Signed-off-by: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/Documentation/filesystems/9p.txt b/Documentation/filesystems/9p.txt
index e694cd1b52cf..d6fd6c6e4244 100644
--- a/Documentation/filesystems/9p.txt
+++ b/Documentation/filesystems/9p.txt
@@ -88,6 +88,16 @@ OPTIONS
                 This can be used to share devices/named pipes/sockets between
                 hosts.  This functionality will be expanded in later versions.
 
+  access        there are three access modes.
+                        user  = if a user tries to access a file on v9fs
+                                filesystem for the first time, v9fs sends an
+                                attach command (Tattach) for that user.
+                                This is the default mode.
+                        <uid> = allows only user with uid=<uid> to access
+                                the files on the mounted filesystem
+                        any   = v9fs does single attach and performs all
+                                operations as one user
+
 RESOURCES
 =========