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[PR #6761] [MERGED] feature: use non-blocking flock calls #6159

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opened 2026-05-05 10:51:50 -06:00 by gitea-mirror · 0 comments
gitea-mirror commented 2026-05-05 10:51:50 -06:00
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📋 Pull Request Information

Original PR: https://github.com/netblue30/firejail/pull/6761
Author: @jlimor-kl
Created: 5/28/2025
Status: ✅ Merged
Merged: 6/22/2025
Merged by: @kmk3

Base: master ← Head: master

📝 Commits (1)

  • 9ea281f feature: use non-blocking flock calls

📊 Changes

1 file changed (+30 additions, -3 deletions)

View changed files

📝 src/firejail/preproc.c (+30 -3)

📄 Description

As reported by @hlein in #6729, if a firejailed process is ^Z'd at the
wrong time during startup, other firejail processes will be unable to
proceed because they'll wait forever for an flock on
/run/firejail/firejail-run.lock.

This builds upon commit f4b8c6dbb ("bugfix: fix potential deadlock with
flock + SIGTSTP (#6750)", 2025-05-21) to add a busy wait while
attempting to acquire a lock. This allows the application to bail out if
it fails to acquire a lock after a given timeout.

Behavior after this patch (we use SIGSTOP, as that cannot be
caught/ignored):

$ firejail --debug id & P=$!;sleep 0.00001;kill -STOP $P
[1] 14411
Looking for kernel processes
Found kthreadd process, we are not running in a sandbox
pid=14411: locking /run/firejail/firejail-run.lock ...
pid=14411: locked /run/firejail/firejail-run.lock

[1]+  Stopped                 firejail --debug id
$ firejail --debug ls
Looking for kernel processes
Found kthreadd process, we are not running in a sandbox
pid=14413: locking /run/firejail/firejail-run.lock ...
pid=14413: sleeping 500us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 1000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 2000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 4000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 8000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 16000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 32000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 64000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 128000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 256000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock
pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock
Error: timeout occurred while trying to lock /run/firejail/firejail-run.lock
Error: ../../src/firejail/preproc.c:112: preproc_lock_file: flock: Resource temporarily unavailable

Enhances commit f4b8c6dbb ("bugfix: fix potential deadlock with flock +
SIGTSTP (#6750)", 2025-05-21).

Suggested-by: @hlein
Co-authored-by: @kmk3

🔄 This issue represents a GitHub Pull Request. It cannot be merged through Gitea due to API limitations.

## 📋 Pull Request Information **Original PR:** https://github.com/netblue30/firejail/pull/6761 **Author:** [@jlimor-kl](https://github.com/jlimor-kl) **Created:** 5/28/2025 **Status:** ✅ Merged **Merged:** 6/22/2025 **Merged by:** [@kmk3](https://github.com/kmk3) **Base:** `master` ← **Head:** `master` --- ### 📝 Commits (1) - [`9ea281f`](https://github.com/netblue30/firejail/commit/9ea281f7033b372fed6ea5a9a41cb360c61c260f) feature: use non-blocking flock calls ### 📊 Changes **1 file changed** (+30 additions, -3 deletions) <details> <summary>View changed files</summary> 📝 `src/firejail/preproc.c` (+30 -3) </details> ### 📄 Description As reported by @hlein in #6729, if a firejailed process is `^Z`'d at the wrong time during startup, other firejail processes will be unable to proceed because they'll wait forever for an flock on `/run/firejail/firejail-run.lock`. This builds upon commit f4b8c6dbb ("bugfix: fix potential deadlock with flock + SIGTSTP (#6750)", 2025-05-21) to add a busy wait while attempting to acquire a lock. This allows the application to bail out if it fails to acquire a lock after a given timeout. Behavior after this patch (we use SIGSTOP, as that cannot be caught/ignored): $ firejail --debug id & P=$!;sleep 0.00001;kill -STOP $P [1] 14411 Looking for kernel processes Found kthreadd process, we are not running in a sandbox pid=14411: locking /run/firejail/firejail-run.lock ... pid=14411: locked /run/firejail/firejail-run.lock [1]+ Stopped firejail --debug id $ firejail --debug ls Looking for kernel processes Found kthreadd process, we are not running in a sandbox pid=14413: locking /run/firejail/firejail-run.lock ... pid=14413: sleeping 500us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 1000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 2000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 4000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 8000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 16000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 32000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 64000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 128000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 256000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock pid=14413: sleeping 500000us while trying to lock /run/firejail/firejail-run.lock Error: timeout occurred while trying to lock /run/firejail/firejail-run.lock Error: ../../src/firejail/preproc.c:112: preproc_lock_file: flock: Resource temporarily unavailable Enhances commit f4b8c6dbb ("bugfix: fix potential deadlock with flock + SIGTSTP (#6750)", 2025-05-21). Suggested-by: @hlein Co-authored-by: @kmk3 --- <sub>🔄 This issue represents a GitHub Pull Request. It cannot be merged through Gitea due to API limitations.</sub>
gitea-mirror 2026-05-05 10:51:50 -06:00
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