[Devel] [PATCH rh8 v2 1/2] ve/device_cgroup: Introduce "devices.extra_list" cgroup file

[Konstantin Khorenko]

Recent versions of containerd (as a part of k3s-1.19.5)
started to apply strict rules when parsing the contents of
'devices.list' files located in the devices cgroup.
Namely, the access token is allowed to contain only those values [rwm],
that are described in
https://www.kernel.org/doc/Documentation/cgroup-v1/devices.txt

In vzkernel we do have an extra permission in device cgroup to allow
mount of a block device inside a Container ('M'), so this upsets
containerd.

Let's leave 'devices.{allow,deny}' files to be able to handle vz
specific "M" permission, but 'devices.list' to show only [rwm]
permissions suppressing possible "M" presence.

Let's introduce another file 'devices.extra_list' to show all
permissions, including possible "M".

 $ echo "b 253:3182 rmM" > devices.allow
 $ cat devices.list
 ...
 b 253:3182 rm
 $ cat devices.extra_list
 ...
 b 253:3182 rmM

https://jira.sw.ru/browse/PSBM-123743

Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>

Changes:
v2: fix DEVCG_DEFAULT_ALLOW branch in devcgroup_seq_show() to show 'M'
    as well in devices::devices.extra_list.
---
 include/linux/device_cgroup.h |  4 ++--
 security/device_cgroup.c      | 15 +++++++++++++--
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/include/linux/device_cgroup.h b/include/linux/device_cgroup.h
index 5a8fb7f78962..5353e22a6ad0 100644
--- a/include/linux/device_cgroup.h
+++ b/include/linux/device_cgroup.h
@@ -6,8 +6,8 @@
 #define DEVCG_ACC_READ  2
 #define DEVCG_ACC_WRITE 4
 #define DEVCG_ACC_MOUNT 64
-#define DEVCG_ACC_MASK (DEVCG_ACC_MKNOD | DEVCG_ACC_READ | DEVCG_ACC_WRITE | \
-			DEVCG_ACC_MOUNT)
+#define DEVCG_ACC_MASK (DEVCG_ACC_MKNOD | DEVCG_ACC_READ | DEVCG_ACC_WRITE)
+#define DEVCG_ACC_EXTRA_MASK (DEVCG_ACC_MASK | DEVCG_ACC_MOUNT)
 
 #define DEVCG_DEV_BLOCK 1
 #define DEVCG_DEV_CHAR  2
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 97dbc72969ce..8a017fc2e1b0 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -230,6 +230,7 @@ static void devcgroup_css_free(struct cgroup_subsys_state *css)
 #define DEVCG_ALLOW 1
 #define DEVCG_DENY 2
 #define DEVCG_LIST 3
+#define DEVCG_EXTRA_LIST 32
 
 #define MAJMINLEN 13
 #define ACCLEN 5
@@ -272,6 +273,11 @@ static int devcgroup_seq_show(struct seq_file *m, void *v)
 	struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
 	struct dev_exception_item *ex;
 	char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
+	short type, mask;
+
+	type = (short)seq_cft(m)->private;
+	mask = (type == DEVCG_EXTRA_LIST) ?
+	        DEVCG_ACC_EXTRA_MASK : DEVCG_ACC_MASK;
 
 	rcu_read_lock();
 	/*
@@ -281,14 +287,14 @@ static int devcgroup_seq_show(struct seq_file *m, void *v)
 	 * This way, the file remains as a "whitelist of devices"
 	 */
 	if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
-		set_access(acc, DEVCG_ACC_MASK);
+		set_access(acc, mask);
 		set_majmin(maj, ~0);
 		set_majmin(min, ~0);
 		seq_printf(m, "%c %s:%s %s\n", type_to_char(DEVCG_DEV_ALL),
 			   maj, min, acc);
 	} else {
 		list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
-			set_access(acc, ex->access);
+			set_access(acc, ex->access & mask);
 			set_majmin(maj, ex->major);
 			set_majmin(min, ex->minor);
 			seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
@@ -799,6 +805,11 @@ static struct cftype dev_cgroup_files[] = {
 		.seq_show = devcgroup_seq_show,
 		.private = DEVCG_LIST,
 	},
+	{
+		.name = "extra_list",
+		.seq_show = devcgroup_seq_show,
+		.private = DEVCG_EXTRA_LIST,
+	},
 	{ }	/* terminate */
 };
 
-- 
2.28.0