[PATCH] autofs: clear O_NONBLOCK on the pipe.

[Ian Kent]

From: NeilBrown <ne...@suse.com>

autofs does not expect the pipe it is given
to have O_NONBLOCK set - specifically if __kernel_write()
in autofs_write() returns -EAGAIN, this is treated
as a fatal error and the pipe is closed.

For safety autofs should, therefore, clear the O_NONBLOCK flag.

Releases of systemd prior to 8th February 2019 used
  pipe2(p, O_NONBLOCK|O_CLOEXEC)
and thus (inadvertently) set this flag.

Signed-off-by: NeilBrown <ne...@suse.com>
Signed-off-by: Ian Kent <ra...@themaw.net>
---
 fs/autofs/autofs_i.h |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/autofs/autofs_i.h b/fs/autofs/autofs_i.h
index b735f2b1e462..70c132acdab1 100644
--- a/fs/autofs/autofs_i.h
+++ b/fs/autofs/autofs_i.h
@@ -216,6 +216,8 @@ static inline int autofs_prepare_pipe(struct file *pipe)
                return -EINVAL;
        /* We want a packet pipe */
        pipe->f_flags |= O_DIRECT;
+       /* We don't expect -EAGAIN */
+       pipe->f_flags &= ~O_NONBLOCK;
        return 0;
 }