device_cgroup: prepare code for bpf-based device controller [Linux 4.15]

This Linux kernel change "device_cgroup: prepare code for bpf-based device controller" is included in the Linux 4.15 release. This change is authored by Roman Gushchin <guro [at] fb.com> on Sun Nov 5 08:15:31 2017 -0500. The commit for this change in Linux stable tree is ecf8fec (patch).

device_cgroup: prepare code for bpf-based device controller

This is non-functional change to prepare the device cgroup code
for adding eBPF-based controller for cgroups v2.

The patch performs the following changes:
1) __devcgroup_inode_permission() and devcgroup_inode_mknod()
   are moving to the device-cgroup.h and converting into static inline.
2) __devcgroup_check_permission() is exported.
3) devcgroup_check_permission() wrapper is introduced to be used
   by both existing and new bpf-based implementations.

Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

There are 108 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 include/linux/device_cgroup.h | 61 ++++++++++++++++++++++++++++++++++++++++---
 security/device_cgroup.c      | 47 ++-------------------------------
 2 files changed, 59 insertions(+), 49 deletions(-)

diff --git a/include/linux/device_cgroup.h b/include/linux/device_cgroup.h
index cdbc344..2d93d7e 100644
--- a/include/linux/device_cgroup.h
+++ b/include/linux/device_cgroup.h
@@ -1,17 +1,70 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #include <linux/fs.h>

+#define DEVCG_ACC_MKNOD 1
+#define DEVCG_ACC_READ  2
+#define DEVCG_ACC_WRITE 4
+#define DEVCG_ACC_MASK (DEVCG_ACC_MKNOD | DEVCG_ACC_READ | DEVCG_ACC_WRITE)
+
+#define DEVCG_DEV_BLOCK 1
+#define DEVCG_DEV_CHAR  2
+#define DEVCG_DEV_ALL   4  /* this represents all devices */
+
+#ifdef CONFIG_CGROUP_DEVICE
+extern int __devcgroup_check_permission(short type, u32 major, u32 minor,
+                   short access);
+#else
+static inline int __devcgroup_check_permission(short type, u32 major, u32 minor,
+                          short access)
+{ return 0; }
+#endif
+
 #ifdef CONFIG_CGROUP_DEVICE
-extern int __devcgroup_inode_permission(struct inode *inode, int mask);
-extern int devcgroup_inode_mknod(int mode, dev_t dev);
+static inline int devcgroup_check_permission(short type, u32 major, u32 minor,
+                        short access)
+{
+   return __devcgroup_check_permission(type, major, minor, access);
+}
+
 static inline int devcgroup_inode_permission(struct inode *inode, int mask)
 {
+   short type, access = 0;
+
    if (likely(!inode->i_rdev))
        return 0;
-   if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
+
+   if (S_ISBLK(inode->i_mode))
+       type = DEVCG_DEV_BLOCK;
+   else if (S_ISCHR(inode->i_mode))
+       type = DEVCG_DEV_CHAR;
+   else
        return 0;
-   return __devcgroup_inode_permission(inode, mask);
+
+   if (mask & MAY_WRITE)
+       access |= DEVCG_ACC_WRITE;
+   if (mask & MAY_READ)
+       access |= DEVCG_ACC_READ;
+
+   return devcgroup_check_permission(type, imajor(inode), iminor(inode),
+                     access);
 }
+
+static inline int devcgroup_inode_mknod(int mode, dev_t dev)
+{
+   short type;
+
+   if (!S_ISBLK(mode) && !S_ISCHR(mode))
+       return 0;
+
+   if (S_ISBLK(mode))
+       type = DEVCG_DEV_BLOCK;
+   else
+       type = DEVCG_DEV_CHAR;
+
+   return devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
+                     DEVCG_ACC_MKNOD);
+}
+
 #else
 static inline int devcgroup_inode_permission(struct inode *inode, int mask)
 { return 0; }
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 968c215..c65b39b 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -15,15 +15,6 @@
 #include <linux/rcupdate.h>
 #include <linux/mutex.h>

-#define DEVCG_ACC_MKNOD 1
-#define DEVCG_ACC_READ  2
-#define DEVCG_ACC_WRITE 4
-#define DEVCG_ACC_MASK (DEVCG_ACC_MKNOD | DEVCG_ACC_READ | DEVCG_ACC_WRITE)
-
-#define DEVCG_DEV_BLOCK 1
-#define DEVCG_DEV_CHAR  2
-#define DEVCG_DEV_ALL   4  /* this represents all devices */
-
 static DEFINE_MUTEX(devcgroup_mutex);

 enum devcg_behavior {
@@ -810,8 +801,8 @@ struct cgroup_subsys devices_cgrp_subsys = {
  *
  * returns 0 on success, -EPERM case the operation is not permitted
  */
-static int __devcgroup_check_permission(short type, u32 major, u32 minor,
-                       short access)
+int __devcgroup_check_permission(short type, u32 major, u32 minor,
+                short access)
 {
    struct dev_cgroup *dev_cgroup;
    bool rc;
@@ -833,37 +824,3 @@ static int __devcgroup_check_permission(short type, u32 major, u32 minor,

    return 0;
 }
-
-int __devcgroup_inode_permission(struct inode *inode, int mask)
-{
-   short type, access = 0;
-
-   if (S_ISBLK(inode->i_mode))
-       type = DEVCG_DEV_BLOCK;
-   if (S_ISCHR(inode->i_mode))
-       type = DEVCG_DEV_CHAR;
-   if (mask & MAY_WRITE)
-       access |= DEVCG_ACC_WRITE;
-   if (mask & MAY_READ)
-       access |= DEVCG_ACC_READ;
-
-   return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
-           access);
-}
-
-int devcgroup_inode_mknod(int mode, dev_t dev)
-{
-   short type;
-
-   if (!S_ISBLK(mode) && !S_ISCHR(mode))
-       return 0;
-
-   if (S_ISBLK(mode))
-       type = DEVCG_DEV_BLOCK;
-   else
-       type = DEVCG_DEV_CHAR;
-
-   return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
-           DEVCG_ACC_MKNOD);
-
-}

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