[PATCH v2 1/1] fanotify: introduce new event flag FAN_EXEC

[Matthew Bobrowski <mbobrowski@mbobrowski.org>]

This is a reduced version of a patch that I originally submitted a while ago.

In short, the fanotify API currently does not provide any means for user space
programs to receive events specifically when a file has been opened with the
intent to be executed. The FAN_EXEC flag will be set within the event mask when
a object has been opened with one of the open flags being __FMODE_EXEC.

Linux is used as an Operating System in some products, with an environment that
can be certified under the Common Criteria Operating System Protection Profile
(OSPP). This is a formal threat model for a class of technology. It requires
specific countermeasures to mitigate threats. It requires documentation to
explain how a product implements these countermeasures. It requires proof via a
test suite to demonstrate that the requirements are met, observed and checked by
an independent qualified third party. The latest set of requirements for OSPP
v4.2 can be found here:

https://www.niap-ccevs.org/Profile/Info.cfm?PPID=424&id=424

If you look on page 58, you will see the following requirement:

FPT_SRP_EXT.1 Software Restriction Policies   FPT_SRP_EXT.1.1

The OS shall restrict execution to only programs which match an administrator
specified [selection:
        file path,
        file digital signature,
        version,
        hash,
        [assignment: other characteristics]
]

This patch is to help aid in meeting this requirement.

Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>

---

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 94b52157bf8d..295549479be7 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -204,6 +204,7 @@ static int fanotify_handle_event(struct fsnotify_group *group,
 	BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
 	BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
 	BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
+	BUILD_BUG_ON(FAN_EXEC != FS_EXEC);

 	if (!fanotify_should_send_event(iter_info, mask, data, data_type))
 		return 0;
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index ababdbfab537..e22324f4642c 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -386,7 +386,7 @@ static __init int fsnotify_init(void)
 {
 	int ret;

-	BUG_ON(hweight32(ALL_FSNOTIFY_EVENTS) != 23);
+	BUG_ON(hweight32(ALL_FSNOTIFY_EVENTS) != 24);

 	ret = init_srcu_struct(&fsnotify_mark_srcu);
 	if (ret)
diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
index fd1ce10553bf..aad174c81322 100644
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -216,6 +216,9 @@ static inline void fsnotify_open(struct file *file)
 	if (S_ISDIR(inode->i_mode))
 		mask |= FS_ISDIR;

+	if (file->f_flags & __FMODE_EXEC)
+		mask |= FS_EXEC;
+
 	fsnotify_parent(path, NULL, mask);
 	fsnotify(inode, mask, path, FSNOTIFY_EVENT_PATH, NULL, 0);
 }
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index b8f4182f42f1..edcdf2fd2328 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -38,6 +38,7 @@
 #define FS_DELETE		0x00000200	/* Subfile was deleted */
 #define FS_DELETE_SELF		0x00000400	/* Self was deleted */
 #define FS_MOVE_SELF		0x00000800	/* Self was moved */
+#define FS_EXEC 		0x00001000	/* File was executed */

 #define FS_UNMOUNT		0x00002000	/* inode on umount fs */
 #define FS_Q_OVERFLOW		0x00004000	/* Event queued overflowed */
@@ -62,7 +63,8 @@
 #define FS_EVENTS_POSS_ON_CHILD   (FS_ACCESS | FS_MODIFY | FS_ATTRIB |\
 				   FS_CLOSE_WRITE | FS_CLOSE_NOWRITE | FS_OPEN |\
 				   FS_MOVED_FROM | FS_MOVED_TO | FS_CREATE |\
-				   FS_DELETE | FS_OPEN_PERM | FS_ACCESS_PERM)
+				   FS_DELETE | FS_OPEN_PERM | FS_ACCESS_PERM |\
+				   FS_EXEC)

 #define FS_MOVE			(FS_MOVED_FROM | FS_MOVED_TO)

@@ -75,7 +77,8 @@
 			     FS_UNMOUNT | FS_Q_OVERFLOW | FS_IN_IGNORED | \
 			     FS_OPEN_PERM | FS_ACCESS_PERM | FS_EXCL_UNLINK | \
 			     FS_ISDIR | FS_IN_ONESHOT | FS_DN_RENAME | \
-			     FS_DN_MULTISHOT | FS_EVENT_ON_CHILD)
+			     FS_DN_MULTISHOT | FS_EVENT_ON_CHILD |\
+			     FS_EXEC)

 struct fsnotify_group;
 struct fsnotify_event;
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index 74247917de04..a850670333fd 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -10,7 +10,7 @@
 #define FAN_CLOSE_WRITE		0x00000008	/* Writtable file closed */
 #define FAN_CLOSE_NOWRITE	0x00000010	/* Unwrittable file closed */
 #define FAN_OPEN		0x00000020	/* File was opened */
-
+#define FAN_EXEC 		0x00001000	/* File was executed */
 #define FAN_Q_OVERFLOW		0x00004000	/* Event queued overflowed */

 #define FAN_OPEN_PERM		0x00010000	/* File open in perm check */
@@ -69,7 +69,8 @@
 #define FAN_ALL_EVENTS (FAN_ACCESS |\
 			FAN_MODIFY |\
 			FAN_CLOSE |\
-			FAN_OPEN)
+			FAN_OPEN |\
+			FAN_EXEC)

 /*
  * All events which require a permission response from userspace