[PATCH] cgroup1: don't call release_agent when it is ""

[PATCH] cgroup1: don't call release_agent when it is ""

[Tycho Andersen]

Older (and maybe current) versions of systemd set release_agent to "" when
shutting down, but do not set notify_on_release to 0.

Since 64e90a8acb85 ("Introduce STATIC_USERMODEHELPER to mediate
call_usermodehelper()"), we filter out such calls when the user mode helper
path is "". However, when used in conjunction with an actual (i.e. non "")
STATIC_USERMODEHELPER, the path is never "", so the real usermode helper
will be called with argv[0] == "".

Let's avoid this by not invoking the release_agent when it is "".

Signed-off-by: Tycho Andersen <tycho@tycho.ws>
---
 kernel/cgroup/cgroup-v1.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index be1a1c83cdd1..b3626c3c6f92 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -782,7 +782,7 @@ void cgroup1_release_agent(struct work_struct *work)
 
 	pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
 	agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
-	if (!pathbuf || !agentbuf)
+	if (!pathbuf || !agentbuf || !strlen(agentbuf))
 		goto out;
 
 	spin_lock_irq(&css_set_lock);
-- 
2.20.1

Re: [PATCH] cgroup1: don't call release_agent when it is ""

[Tejun Heo]

On Wed, Feb 19, 2020 at 12:01:29PM -0700, Tycho Andersen wrote:
> Older (and maybe current) versions of systemd set release_agent to "" when
> shutting down, but do not set notify_on_release to 0.
> 
> Since 64e90a8acb85 ("Introduce STATIC_USERMODEHELPER to mediate
> call_usermodehelper()"), we filter out such calls when the user mode helper
> path is "". However, when used in conjunction with an actual (i.e. non "")
> STATIC_USERMODEHELPER, the path is never "", so the real usermode helper
> will be called with argv[0] == "".
> 
> Let's avoid this by not invoking the release_agent when it is "".
> 
> Signed-off-by: Tycho Andersen <tycho@tycho.ws>

Applied to cgroup/for-5.6-fixes.

Thanks.

-- 
tejun