[PATCH] fanotify: move path permission and security check

[Mete Durlu <meted@linux.ibm.com>]

In current state do_fanotify_mark() does path permission and security
checking before doing the event configuration checks. In the case
where user configures mount and sb marks with kernel internal pseudo
fs, security_path_notify() yields an EACESS and causes an earlier
exit. Instead, this particular case should have been handled by
fanotify_events_supported() and exited with an EINVAL.
Move path perm and security checks under the event validation to
prevent this from happening.
Simple reproducer;

	fan_d = fanotify_init(FAN_CLASS_NOTIF, O_RDONLY);
	pipe2(pipes, O_CLOEXEC);
        fanotify_mark(fan_d,
		      FAN_MARK_ADD |
		      FAN_MARK_MOUNT,
		      FAN_ACCESS,
		      pipes[0],
		      NULL);
	// expected: EINVAL (22), produces: EACCES (13)
        printf("mark errno: %d\n", errno);

Another reproducer;
ltp/testcases/kernel/syscalls/fanotify/fanotify14

Fixes: 69562eb0bd3e ("fanotify: disallow mount/sb marks on kernel internal pseudo fs")

Signed-off-by: Mete Durlu <meted@linux.ibm.com>
---
 fs/notify/fanotify/fanotify_user.c | 24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index fbdc63cc10d9..14121ad0e10d 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -1015,7 +1015,7 @@ static int fanotify_find_path(int dfd, const char __user *filename,
 			fdput(f);
 			goto out;
 		}
-
+		ret = 0;
 		*path = f.file->f_path;
 		path_get(path);
 		fdput(f);
@@ -1028,21 +1028,7 @@ static int fanotify_find_path(int dfd, const char __user *filename,
 			lookup_flags |= LOOKUP_DIRECTORY;
 
 		ret = user_path_at(dfd, filename, lookup_flags, path);
-		if (ret)
-			goto out;
 	}
-
-	/* you can only watch an inode if you have read permissions on it */
-	ret = path_permission(path, MAY_READ);
-	if (ret) {
-		path_put(path);
-		goto out;
-	}
-
-	ret = security_path_notify(path, mask, obj_type);
-	if (ret)
-		path_put(path);
-
 out:
 	return ret;
 }
@@ -1894,6 +1880,14 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
 		if (ret)
 			goto path_put_and_out;
 	}
+	/* you can only watch an inode if you have read permissions on it */
+	ret = path_permission(&path, MAY_READ);
+	if (ret)
+		goto path_put_and_out;
+
+	ret = security_path_notify(&path, mask, obj_type);
+	if (ret)
+		goto path_put_and_out;
 
 	if (fid_mode) {
 		ret = fanotify_test_fsid(path.dentry, flags, &__fsid);
-- 
2.40.1