linux-kernel - [PATCH] kernel/taskstats: fix wrong nla type for {cgroup,task}stats policy

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Date:   Wed, 25 Mar 2020 22:50:42 -0400
From:   Yafang Shao <laoar.shao@...il.com>
To:     bsingharora@...il.com, akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, Yafang Shao <laoar.shao@...il.com>,
        stable@...r.kernel.org
Subject: [PATCH] kernel/taskstats: fix wrong nla type for {cgroup,task}stats policy

After our server is upgraded to a newer kernel, we found that it
continuesly print a warning in the kernel message. The warning is,
[832984.946322] netlink: 'irmas.lc': attribute type 1 has an invalid length.

irmas.lc is one of our container monitor daemons, and it will use
CGROUPSTATS_CMD_GET to get the cgroupstats, that is similar with
tools/accounting/getdelays.c. We can also produce this warning with
getdelays. For example, after running bellow command
	$ ./getdelays -C /sys/fs/cgroup/memory
then you can find a warning in dmesg,
[61607.229318] netlink: 'getdelays': attribute type 1 has an invalid length.

This warning is introduced in commit 6e237d099fac ("netlink: Relax attr
validation for fixed length types"), which is used to check whether
attributes using types NLA_U* and NLA_S* have an exact length.

Regarding this issue, the root cause is cgroupstats_cmd_get_policy defines
a wrong type as NLA_U32, while it should be NLA_NESTED an its minimal
length is NLA_HDRLEN. That is similar to taskstats_cmd_get_policy.

As this behavior change really breaks our application, we'd better
cc stable as well.

Signed-off-by: Yafang Shao <laoar.shao@...il.com>
Cc: stable@...r.kernel.org
---
 kernel/taskstats.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index e2ac0e3..b90a520 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -35,8 +35,8 @@
 static struct genl_family family;
 
 static const struct nla_policy taskstats_cmd_get_policy[TASKSTATS_CMD_ATTR_MAX+1] = {
-	[TASKSTATS_CMD_ATTR_PID]  = { .type = NLA_U32 },
-	[TASKSTATS_CMD_ATTR_TGID] = { .type = NLA_U32 },
+	[TASKSTATS_CMD_ATTR_PID]  = { .type = NLA_NESTED },
+	[TASKSTATS_CMD_ATTR_TGID] = { .type = NLA_NESTED },
 	[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK] = { .type = NLA_STRING },
 	[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK] = { .type = NLA_STRING },};
 
@@ -45,7 +45,7 @@
  * Make sure they are always aligned.
  */
 static const struct nla_policy cgroupstats_cmd_get_policy[TASKSTATS_CMD_ATTR_MAX+1] = {
-	[CGROUPSTATS_CMD_ATTR_FD] = { .type = NLA_U32 },
+	[CGROUPSTATS_CMD_ATTR_FD] = { .type = NLA_NESTED },
 };
 
 struct listener {
-- 
1.8.3.1