fanotify: cleanups for fanotify_mark() input validations

Create helper fanotify_may_update_existing_mark() for checking for
conflicts between existing mark flags and fanotify_mark() flags.

Use variable mark_cmd to make the checks for mark command bits
cleaner.

Link: https://lore.kernel.org/r/20220629144210.2983229-3-amir73il@gmail.comSigned-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/notify/fanotify/fanotify_user.c

@@ -1187,6 +1187,19 @@ static int fanotify_group_init_error_pool(struct fsnotify_group *group)
 					 sizeof(struct fanotify_error_event));
 }
 
+static int fanotify_may_update_existing_mark(struct fsnotify_mark *fsn_mark,
+					      unsigned int fan_flags)
+{
+	/*
+	 * Non evictable mark cannot be downgraded to evictable mark.
+	 */
+	if (fan_flags & FAN_MARK_EVICTABLE &&
+	    !(fsn_mark->flags & FSNOTIFY_MARK_FLAG_NO_IREF))
+		return -EEXIST;
+
+	return 0;
+}
+
 static int fanotify_add_mark(struct fsnotify_group *group,
 			     fsnotify_connp_t *connp, unsigned int obj_type,
 			     __u32 mask, unsigned int fan_flags,
@@ -1208,13 +1221,11 @@ static int fanotify_add_mark(struct fsnotify_group *group,
 	}
 
 	/*
-	 * Non evictable mark cannot be downgraded to evictable mark.
+	 * Check if requested mark flags conflict with an existing mark flags.
 	 */
-	if (fan_flags & FAN_MARK_EVICTABLE &&
-	    !(fsn_mark->flags & FSNOTIFY_MARK_FLAG_NO_IREF)) {
-		ret = -EEXIST;
+	ret = fanotify_may_update_existing_mark(fsn_mark, fan_flags);
+	if (ret)
 		goto out;
-	}
 
 	/*
 	 * Error events are pre-allocated per group, only if strictly
@@ -1557,6 +1568,7 @@ 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 ignore = flags & FAN_MARK_IGNORED_MASK;
 	unsigned int obj_type, fid_mode;
 	u32 umask = 0;
@@ -1586,7 +1598,7 @@ 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)) {
+	switch (mark_cmd) {
 	case FAN_MARK_ADD:
 	case FAN_MARK_REMOVE:
 		if (!mask)
@@ -1675,7 +1687,7 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
 	if (mask & FAN_RENAME && !(fid_mode & FAN_REPORT_NAME))
 		goto fput_and_out;
 
-	if (flags & FAN_MARK_FLUSH) {
+	if (mark_cmd == FAN_MARK_FLUSH) {
 		ret = 0;
 		if (mark_type == FAN_MARK_MOUNT)
 			fsnotify_clear_vfsmount_marks_by_group(group);
@@ -1691,7 +1703,7 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
 	if (ret)
 		goto fput_and_out;
 
-	if (flags & FAN_MARK_ADD) {
+	if (mark_cmd == FAN_MARK_ADD) {
 		ret = fanotify_events_supported(group, &path, mask, flags);
 		if (ret)
 			goto path_put_and_out;
@@ -1729,7 +1741,7 @@ 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,

include/linux/fanotify.h

@@ -59,15 +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_EVICTABLE | \
-				 FAN_MARK_FLUSH)
+				 FAN_MARK_EVICTABLE)
 
 /*
  * Events that can be reported with data type FSNOTIFY_EVENT_PATH.