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Subject[GIT PULL] security: device_cgroup RCU warning fix
This was posted a while back and been baking in -next for a while, please 
consider for 5.9.


The following changes since commit bcf876870b95592b52519ed4aafcf9d95999bc9c:

Linux 5.8 (2020-08-02 14:21:45 -0700)

are available in the Git repository at:

git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git tags/fixes-v5.9a

for you to fetch changes up to bc62d68e2a0a69fcdcf28aca8edb01abf306b698:

device_cgroup: Fix RCU list debugging warning (2020-08-20 11:25:03 -0700)

----------------------------------------------------------------
device_cgroup RCU warning fix from Amol Grover <frextrite@gmail.com>

----------------------------------------------------------------

Amol Grover (1):
device_cgroup: Fix RCU list debugging warning

security/device_cgroup.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)


commit bc62d68e2a0a69fcdcf28aca8edb01abf306b698
Author: Amol Grover <frextrite@gmail.com>
Date: Mon Apr 6 16:29:50 2020 +0530

device_cgroup: Fix RCU list debugging warning

exceptions may be traversed using list_for_each_entry_rcu()
outside of an RCU read side critical section BUT under the
protection of decgroup_mutex. Hence add the corresponding
lockdep expression to fix the following false-positive
warning:

[ 2.304417] =============================
[ 2.304418] WARNING: suspicious RCU usage
[ 2.304420] 5.5.4-stable #17 Tainted: G E
[ 2.304422] -----------------------------
[ 2.304424] security/device_cgroup.c:355 RCU-list traversed in non-reader section!!

Signed-off-by: Amol Grover <frextrite@gmail.com>
Signed-off-by: James Morris <jmorris@namei.org>

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 43ab0ad45c1b..04375df52fc9 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -354,7 +354,8 @@ static bool match_exception_partial(struct list_head *exceptions, short type,
{
struct dev_exception_item *ex;

- list_for_each_entry_rcu(ex, exceptions, list) {
+ list_for_each_entry_rcu(ex, exceptions, list,
+ lockdep_is_held(&devcgroup_mutex)) {
if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
continue;
if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
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