cgroup1: don't call release_agent when it is ""

[ Upstream commit 2e5383d7904e60529136727e49629a82058a5607 ]

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>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 84bedb87ae137284b024dfe32e1353a4a034755b..a1fbf500d0af7f34b487a12b2d530b8df845fa46 100644 (file)
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -785,7 +785,7 @@ 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);