[PATCH proxmox] fix #6267: rest-server: fix task log rotation race

["Fabian Grünbichler" <f.gruenbichler@proxmox.com>]

if the task log archive files get rotated, the base `archive` file is renamed
to `archive.1`. until it is recreated, iterating over the archive files returns
no files.

on systems with a lot of task activity, task rotation could be effectively
broken:
- every logrotate task rotated the task archive files
- the subsequent handling of the archive files to find out which task logs to
  clean found no task archive files at all - only rotated copies existed

there's a small race window in rotation task:
- archives are rotated (and too old archives removed)
- old task logs are cleaned up

if the base archive file got recreated inbetween (e.g., by an unrelated task
finishing), then log rotation would clean up old task logs despite the bug.

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---

Notes:
    confirmed the problematic sequence by adding a sleep at the end of the
    logrotate task in PBS, with an otherwise quiet system the archive file gets
    rotated but not recreated until the tasks exits, and not ask log cleanup
    happens.
    
    with this patch in place, old task logs get cleaned up as expected.

 proxmox-rest-server/src/worker_task.rs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/proxmox-rest-server/src/worker_task.rs b/proxmox-rest-server/src/worker_task.rs
index 63f0c14c..a901985b 100644
--- a/proxmox-rest-server/src/worker_task.rs
+++ b/proxmox-rest-server/src/worker_task.rs
@@ -303,6 +303,21 @@ pub fn rotate_task_log_archive(
 
     let mut rotated = logrotate.rotate(size_threshold)?;
 
+    // need to recreate base file after rotation
+    if rotated {
+        let options = setup
+            .file_opts
+            .perm(nix::sys::stat::Mode::from_bits_truncate(0o660));
+
+        atomic_open_or_create_file(
+            &setup.task_archive_fn,
+            OFlag::O_APPEND | OFlag::O_RDWR,
+            &[],
+            options,
+            false,
+        )?;
+    }
+
     if let Some(max_days) = max_days {
         // NOTE: not on exact day-boundary but close enough for what's done here
         let cutoff_time = proxmox_time::epoch_i64() - (max_days * 24 * 60 * 60) as i64;
-- 
2.47.3