2014-02-17 02:42:37

by Zefan Li

Subject: [PATCH] cgroup: add a validation check to cgroup_add_cftyps()

Fengguang reported this bug:

BUG: unable to handle kernel NULL pointer dereference at 0000003c
IP: [<cc90b4ad>] cgroup_cfts_commit+0x27/0x1c1
...
Call Trace:
[<cc9d1129>] ? kmem_cache_alloc_trace+0x33f/0x3b7
[<cc90c6fc>] cgroup_add_cftypes+0x8f/0xca
[<cd78b646>] cgroup_init+0x6a/0x26a
[<cd764d7d>] start_kernel+0x4d7/0x57a
[<cd7642ef>] i386_start_kernel+0x92/0x96

This happens in a corner case. If CGROUP_SCHED=y but CFS_BANDWIDTH=n &&
FAIR_GROUP_SCHED=n && RT_GROUP_SCHED=n, we have:

cpu_files[] = {
{ } /* terminate */
}

When we pass cpu_files to cgroup_apply_cftypes(), as cpu_files[0].ss
is NULL, we'll access NULL pointer.

The bug was introduced by commit de00ffa56ea3132c6013fc8f07133b8a1014cf53
("cgroup: make cgroup_subsys->base_cftypes use cgroup_add_cftypes()").

Reported-by: Fengguang Wu <[email protected]>
Signed-off-by: Li Zefan <[email protected]>
---
kernel/cgroup.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index eaffc08..465c1d8 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2356,6 +2356,9 @@ int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
{
int ret;

+ if (!cfts || cfts[0].name[0] == '\0')
+ return 0;
+
ret = cgroup_init_cftypes(ss, cfts);
if (ret)
return ret;
--
1.8.0.2

2014-02-18 23:21:05

by Tejun Heo

Subject: Re: [PATCH] cgroup: add a validation check to cgroup_add_cftyps()

On Mon, Feb 17, 2014 at 10:41:50AM +0800, Li Zefan wrote:
> Fengguang reported this bug:
>
> BUG: unable to handle kernel NULL pointer dereference at 0000003c
> IP: [<cc90b4ad>] cgroup_cfts_commit+0x27/0x1c1
> ...
> Call Trace:
> [<cc9d1129>] ? kmem_cache_alloc_trace+0x33f/0x3b7
> [<cc90c6fc>] cgroup_add_cftypes+0x8f/0xca
> [<cd78b646>] cgroup_init+0x6a/0x26a
> [<cd764d7d>] start_kernel+0x4d7/0x57a
> [<cd7642ef>] i386_start_kernel+0x92/0x96
>
> This happens in a corner case. If CGROUP_SCHED=y but CFS_BANDWIDTH=n &&
> FAIR_GROUP_SCHED=n && RT_GROUP_SCHED=n, we have:
>
> cpu_files[] = {
> { } /* terminate */
> }
>
> When we pass cpu_files to cgroup_apply_cftypes(), as cpu_files[0].ss
> is NULL, we'll access NULL pointer.
>
> The bug was introduced by commit de00ffa56ea3132c6013fc8f07133b8a1014cf53
> ("cgroup: make cgroup_subsys->base_cftypes use cgroup_add_cftypes()").
>
> Reported-by: Fengguang Wu <[email protected]>
> Signed-off-by: Li Zefan <[email protected]>

Applied to cgroup/for-3.15. Thanks.

--
tejun