[Galene] forbid presenting probably bug

[Z0T <zot@mochela.it>]

Hi,

I think I found a bug in Galene 1.2.1 (also present on master as of 
d2c34df, 4 October 2026): removing a permission from one client 
(unpresent, unop, shutup) can also change the permissions of other 
clients, including clients that join later.

How to reproduce, with a group that has a wildcard user with permissions 
"present":

   1. An operator and a guest ("anna") join; the guest gets ["present", 
"message"].
   2. The operator does "Forbid presenting" (useraction "unpresent") on 
anna.
   3. Another guest ("bruno") joins with the same wildcard password.

bruno gets ["message", "message"] instead of ["present", "message"]: he 
cannot present, and every guest joining after him gets the same, until 
Galene is restarted.

The same happens with stateful tokens: after "unpresent" on one client 
that joined with a token, the other clients that joined with the same 
token lose "present" on the server side (without receiving a 
"joined"/"change" message), and so do new clients joining with that token.

Cause: remove() in rtpconn/webclient.go does append(l[:i], l[i+1:]...), 
which modifies the backing array in place. But c.permissions is not 
always a private slice: Permissions.Permissions() in 
group/description.go returns permissionsMap[p.name] directly (unless 
"record" or "token" is prepended), and for stateful tokens the slice 
comes from the token itself. So unpresent on one client rewrites 
permissionsMap["present"] (or the token's permissions) for everyone. 
addnew() can write into the same shared array afterwards, when its 
capacity allows.

The smallest fix I found is to copy the slice before changing it:

--- a/rtpconn/webclient.go
+++ b/rtpconn/webclient.go
@@ -1216,6 +1216,10 @@
              }
          }
      case changePermissionsAction:
+        // c.permissions may share its backing array with other clients
+        // (permissionsMap, stateful tokens): remove and addnew modify it
+        // in place, so make a private copy first.
+        c.permissions = slices.Clone(c.permissions)
          switch a.kind {
          case "op":
              c.permissions = addnew("op", c.permissions)

With this change, in the scenario above bruno gets ["present", 
"message"], and the clients sharing a token keep their permissions. We 
have been running it in production since today. Perhaps you would prefer 
to fix it at the source instead (Permissions() returning a copy, or 
remove() not working in place); either is fine with us.

Thanks for Galene,

Alberto Brusoni
mochela.it