mknod: take sanity checks on mode into the very beginning

Note that applying umask can't affect their results.  While
that affects errno in cases like
	mknod("/no_such_directory/a", 030000)
yielding -EINVAL (due to impossible mode_t) instead of
-ENOENT (due to inexistent directory), IMO that makes a lot
more sense, POSIX allows to return either and any software
that relies on getting -ENOENT instead of -EINVAL in that
case deserves everything it gets.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 3 insertions, 5 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 5bc6f3d1dc8a..cf362dc9d1fd 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2964,8 +2964,9 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
         struct path path;
         int error;
 
-        if (S_ISDIR(mode))
-                return -EPERM;
+        error = may_mknod(mode);
+        if (error)
+                return error;
 
         dentry = user_path_create(dfd, filename, &path, 0);
         if (IS_ERR(dentry))
@@ -2973,9 +2974,6 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
 
         if (!IS_POSIXACL(path.dentry->d_inode))
                 mode &= ~current_umask();
-        error = may_mknod(mode);
-        if (error)
-                goto out_dput;
         error = mnt_want_write(path.mnt);
         if (error)
                 goto out_dput;