If fuse daemon is started with cache=never, fuse falls back to direct IO.
In that write path we don't call file_remove_privs() and that means setuid
bit is not cleared if unpriviliged user writes to a file with setuid bit set.

pjdfstest chmod test 12.t tests this and fails.

Fix this by calling fuse_remove_privs() even for direct I/O path.

I tested this as follows.

- Run fuse example pasthrough fs.

  $ passthrough_ll /mnt/pasthrough-mnt -o 
default_permissions,allow_other,cache=never
  $ mkdir /mnt/pasthrough-mnt/testdir
  $ cd /mnt/pasthrough-mnt/testdir
  $ prove -rv pjdfstests/tests/chmod/12.t

Signed-off-by: Vivek Goyal <vgo...@redhat.com>
---
 fs/fuse/file.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 06096b60f1df..5baf07fd2876 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1456,14 +1456,18 @@ static ssize_t fuse_direct_write_iter(struct kiocb 
*iocb, struct iov_iter *from)
        /* Don't allow parallel writes to the same file */
        inode_lock(inode);
        res = generic_write_checks(iocb, from);
-       if (res > 0) {
-               if (!is_sync_kiocb(iocb) && iocb->ki_flags & IOCB_DIRECT) {
-                       res = fuse_direct_IO(iocb, from);
-               } else {
-                       res = fuse_direct_io(&io, from, &iocb->ki_pos,
-                                            FUSE_DIO_WRITE);
-               }
+       if (res <= 0)
+               goto out;
+
+       res = file_remove_privs(iocb->ki_filp);
+       if (res)
+               goto out;
+       if (!is_sync_kiocb(iocb) && iocb->ki_flags & IOCB_DIRECT) {
+               res = fuse_direct_IO(iocb, from);
+       } else {
+               res = fuse_direct_io(&io, from, &iocb->ki_pos, FUSE_DIO_WRITE);
        }
+out:
        fuse_invalidate_attr(inode);
        if (res > 0)
                fuse_write_update_size(inode, iocb->ki_pos);
-- 
2.20.1

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