From: Jiri Slaby <jslaby@xxxxxxx>
Commit "device_cgroup: convert device_cgroup internally to policy +
exceptions" removed rcu locks which are needed in task_devcgroup
called in this chain: devcgroup_inode_mknod OR
__devcgroup_inode_permission -> __devcgroup_inode_permission ->
task_devcgroup -> task_subsys_state -> task_subsys_state_check.
Change the code so that task_devcgroup is safely called with rcu read
lock held.
===============================
[ INFO: suspicious RCU usage. ]
3.6.0-rc5-next-20120913+ #42 Not tainted
-------------------------------
include/linux/cgroup.h:553 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 1, debug_locks = 0
2 locks held by kdevtmpfs/23:
#0: (sb_writers){.+.+.+}, at: [<ffffffff8116873f>]
mnt_want_write+0x1f/0x50
#1: (&sb->s_type->i_mutex_key#3/1){+.+.+.}, at: [<ffffffff811558af>]
kern_path_create+0x7f/0x170
stack backtrace:
Pid: 23, comm: kdevtmpfs Not tainted 3.6.0-rc5-next-20120913+ #42
Call Trace:
[<ffffffff810c638d>] lockdep_rcu_suspicious+0xfd/0x130
[<ffffffff8121541d>] devcgroup_inode_mknod+0x19d/0x240
[<ffffffff8107bf54>] ? ns_capable+0x44/0x80
[<ffffffff81156b21>] vfs_mknod+0x71/0xf0
[<ffffffff813a8332>] handle_create.isra.2+0x72/0x200
[<ffffffff813a85d4>] devtmpfsd+0x114/0x140
[<ffffffff813a84c0>] ? handle_create.isra.2+0x200/0x200
[<ffffffff81093ad6>] kthread+0xd6/0xe0
[<ffffffff81654f24>] kernel_thread_helper+0x4/0x10
[<ffffffff8165369d>] ? retint_restore_args+0xe/0xe
[<ffffffff81093a00>] ? kthread_create_on_node+0x140/0x140
[<ffffffff81654f20>] ? gs_change+0xb/0xb
Cc: Dave Jones <davej@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Li Zefan <lizefan@xxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxx>
Cc: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
And this should fix it.
security/device_cgroup.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
--- github.orig/security/device_cgroup.c 2012-10-17 11:11:08.514793906 -0400
+++ github/security/device_cgroup.c 2012-10-19 16:35:37.936804289 -0400
@@ -533,10 +533,10 @@ struct cgroup_subsys devices_subsys = {
*
* returns 0 on success, -EPERM case the operation is not permitted
*/
-static int __devcgroup_check_permission(struct dev_cgroup *dev_cgroup,
- short type, u32 major, u32 minor,
+static int __devcgroup_check_permission(short type, u32 major, u32 minor,
short access)
{
+ struct dev_cgroup *dev_cgroup;
struct dev_exception_item ex;
int rc;
@@ -547,6 +547,7 @@ memset(&ex, 0, sizeof(ex));
ex.access = access;
rcu_read_lock();
+ dev_cgroup = task_devcgroup(current);
rc = may_access(dev_cgroup, &ex);
rcu_read_unlock();
@@ -558,7 +559,6 @@ return 0;
int __devcgroup_inode_permission(struct inode *inode, int mask)
{
- struct dev_cgroup *dev_cgroup = task_devcgroup(current);
short type, access = 0;
if (S_ISBLK(inode->i_mode))
@@ -570,13 +570,12 @@ short type, access = 0;
if (mask & MAY_READ)
access |= ACC_READ;
- return __devcgroup_check_permission(dev_cgroup, type, imajor(inode),
- iminor(inode), access);
+ return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
+ access);
}
int devcgroup_inode_mknod(int mode, dev_t dev)
{
- struct dev_cgroup *dev_cgroup = task_devcgroup(current);
short type;
if (!S_ISBLK(mode) && !S_ISCHR(mode))
@@ -587,7 +586,7 @@ return 0;
else
type = DEV_CHAR;
- return __devcgroup_check_permission(dev_cgroup, type, MAJOR(dev),
- MINOR(dev), ACC_MKNOD);
+ return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
+ ACC_MKNOD);
}
--
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