[PATCH 4/5] fanotify: add support for exclusive create of mark

[Amir Goldstein <amir73il@gmail.com>]

Similar to inotify's IN_MARK_CREATE, adding an fanotify mark with flag
FAN_MARK_CREATE will fail with error EEXIST if an fanotify mark already
exists on the object.

Unlike inotify's IN_MARK_CREATE, FAN_MARK_CREATE has to supplied in
combination with FAN_MARK_ADD (FAN_MARK_ADD is like inotify_add_watch()
and the behavior of IN_MARK_ADD is the default for fanotify_mark()).

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/fanotify/fanotify_user.c | 13 ++++++++++---
 include/linux/fanotify.h           |  8 +++++---
 include/uapi/linux/fanotify.h      |  1 +
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 9b32b76a9c30..99c5ced6abd8 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -1185,6 +1185,9 @@ static int fanotify_add_mark(struct fsnotify_group *group,
 			mutex_unlock(&group->mark_mutex);
 			return PTR_ERR(fsn_mark);
 		}
+	} else if (flags & FAN_MARK_CREATE) {
+		ret = -EEXIST;
+		goto out;
 	}
 
 	/*
@@ -1510,6 +1513,7 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
 	__kernel_fsid_t __fsid, *fsid = NULL;
 	u32 valid_mask = FANOTIFY_EVENTS | FANOTIFY_EVENT_FLAGS;
 	unsigned int mark_type = flags & FANOTIFY_MARK_TYPE_BITS;
+	unsigned int mark_cmd = flags & FANOTIFY_MARK_CMD_BITS;
 	bool ignored = flags & FAN_MARK_IGNORED_MASK;
 	unsigned int obj_type, fid_mode;
 	u32 umask = 0;
@@ -1539,7 +1543,10 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
 		return -EINVAL;
 	}
 
-	switch (flags & (FAN_MARK_ADD | FAN_MARK_REMOVE | FAN_MARK_FLUSH)) {
+	if (flags & FAN_MARK_CREATE && mark_cmd != FAN_MARK_ADD)
+		return -EINVAL;
+
+	switch (mark_cmd) {
 	case FAN_MARK_ADD:
 	case FAN_MARK_REMOVE:
 		if (!mask)
@@ -1671,7 +1678,7 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
 	}
 
 	/* create/update an inode mark */
-	switch (flags & (FAN_MARK_ADD | FAN_MARK_REMOVE)) {
+	switch (mark_cmd) {
 	case FAN_MARK_ADD:
 		if (mark_type == FAN_MARK_MOUNT)
 			ret = fanotify_add_vfsmount_mark(group, mnt, mask,
@@ -1749,7 +1756,7 @@ static int __init fanotify_user_setup(void)
 
 	BUILD_BUG_ON(FANOTIFY_INIT_FLAGS & FANOTIFY_INTERNAL_GROUP_FLAGS);
 	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 12);
-	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 9);
+	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 10);
 
 	fanotify_mark_cache = KMEM_CACHE(fsnotify_mark,
 					 SLAB_PANIC|SLAB_ACCOUNT);
diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index 419cadcd7ff5..780f4b17d4c9 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -59,14 +59,16 @@
 #define FANOTIFY_MARK_TYPE_BITS	(FAN_MARK_INODE | FAN_MARK_MOUNT | \
 				 FAN_MARK_FILESYSTEM)
 
+#define FANOTIFY_MARK_CMD_BITS	(FAN_MARK_ADD | FAN_MARK_REMOVE | \
+				 FAN_MARK_FLUSH)
+
 #define FANOTIFY_MARK_FLAGS	(FANOTIFY_MARK_TYPE_BITS | \
-				 FAN_MARK_ADD | \
-				 FAN_MARK_REMOVE | \
+				 FANOTIFY_MARK_CMD_BITS | \
 				 FAN_MARK_DONT_FOLLOW | \
 				 FAN_MARK_ONLYDIR | \
 				 FAN_MARK_IGNORED_MASK | \
 				 FAN_MARK_IGNORED_SURV_MODIFY | \
-				 FAN_MARK_FLUSH)
+				 FAN_MARK_CREATE)
 
 /*
  * Events that can be reported with data type FSNOTIFY_EVENT_PATH.
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index e8ac38cc2fd6..c41feac21fe9 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -82,6 +82,7 @@
 #define FAN_MARK_IGNORED_SURV_MODIFY	0x00000040
 #define FAN_MARK_FLUSH		0x00000080
 /* FAN_MARK_FILESYSTEM is	0x00000100 */
+#define FAN_MARK_CREATE		0x00000200
 
 /* These are NOT bitwise flags.  Both bits can be used togther.  */
 #define FAN_MARK_INODE		0x00000000
-- 
2.25.1