[PATCH proxmox-backup 10/28] api: backup: fix possible information leak in multi-tenant datastores

[Christian Ebner <c.ebner@proxmox.com>]

Do not leak the owner of the group in permission checks on backup, as
a user with Datastore.Backup only permissions should never be able to
see other users. This is especially of interest if users gained
unintended access to a namespace they should not be allowed to, e.g.
due to misconfiguration.

Rather include the namespace and group information.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 src/api2/backup/mod.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/api2/backup/mod.rs b/src/api2/backup/mod.rs
index 4d3db731b..fe01636d6 100644
--- a/src/api2/backup/mod.rs
+++ b/src/api2/backup/mod.rs
@@ -155,8 +155,13 @@ fn upgrade_to_backup_protocol(
         let correct_owner =
             owner == auth_id || (owner.is_token() && Authid::from(owner.user().clone()) == auth_id);
         if !correct_owner && worker_type != "benchmark" {
+            let namespace_and_group = if !backup_group.backup_ns().is_root() {
+                format!("[{}]:{}", backup_group.backup_ns(), backup_group.group())
+            } else {
+                backup_group.group().to_string()
+            };
             // only the owner is allowed to create additional snapshots
-            bail!("backup owner check failed ({} != {})", auth_id, owner);
+            bail!("backup owner check failed: {namespace_and_group} not owned by {auth_id}");
         }
 
         let last_backup = {
-- 
2.47.3