[PATCH 1/2] cgroups: Fix to return errno in a failure path

Li Zefan lizf at cn.fujitsu.com
Tue Jan 26 00:16:44 PST 2010


In cgroup_create(), if alloc_css_id() returns failure, the errno
is not propagated to userspace, so mkdir will fail silently.

To trigger this bug, we mount blkio (or memory subsystem), and
create more then 65534 cgroups. (The number of cgroups is limited
to 65535 if a subsystem has use_id == 1)

 # mount -t cgroup -o blkio xxx /mnt
 # for ((i = 0; i < 65534; i++)); do mkdir /mnt/$i; done
 # mkdir /mnt/65534
 (should return ENOSPC)
 #

Signed-off-by: Li Zefan <lizf at cn.fujitsu.com>
---
 cgroup.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/kernel/cgroup.c.orig	2010-01-19 16:37:37.000000000 +0800
+++ a/kernel/cgroup.c	2010-01-19 16:39:07.000000000 +0800
@@ -3279,14 +3279,17 @@ static long cgroup_create(struct cgroup 
 
 	for_each_subsys(root, ss) {
 		struct cgroup_subsys_state *css = ss->create(ss, cgrp);
+
 		if (IS_ERR(css)) {
 			err = PTR_ERR(css);
 			goto err_destroy;
 		}
 		init_cgroup_css(css, ss, cgrp);
-		if (ss->use_id)
-			if (alloc_css_id(ss, parent, cgrp))
+		if (ss->use_id) {
+			err = alloc_css_id(ss, parent, cgrp);
+			if (err)
 				goto err_destroy;
+		}
 		/* At error, ->destroy() callback has to free assigned ID. */
 	}
 


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