cgroup: Replace all non-returning strlcpy with strscpy

strlcpy() reads the entire source buffer first.
This read may exceed the destination size limit.
This is both inefficient and can lead to linear read
overflows if a source string is not NUL-terminated [1].
In an effort to remove strlcpy() completely [2], replace
strlcpy() here with strscpy().
No return values were used, so direct replacement is safe.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
[2] https://github.com/KSPP/linux/issues/89

Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/cgroup-v1.c

@@ -563,7 +563,7 @@ static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
 	if (!cgrp)
 		return -ENODEV;
 	spin_lock(&release_agent_path_lock);
-	strlcpy(cgrp->root->release_agent_path, strstrip(buf),
+	strscpy(cgrp->root->release_agent_path, strstrip(buf),
 		sizeof(cgrp->root->release_agent_path));
 	spin_unlock(&release_agent_path_lock);
 	cgroup_kn_unlock(of->kn);
@@ -797,7 +797,7 @@ void cgroup1_release_agent(struct work_struct *work)
 		goto out_free;
 
 	spin_lock(&release_agent_path_lock);
-	strlcpy(agentbuf, cgrp->root->release_agent_path, PATH_MAX);
+	strscpy(agentbuf, cgrp->root->release_agent_path, PATH_MAX);
 	spin_unlock(&release_agent_path_lock);
 	if (!agentbuf[0])
 		goto out_free;