[PATCH v3] userfaultfd: uapi: fix UFFDIO_CONTINUE ioctl request definition

[Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>]

This ioctl request reads from uffdio_continue structure written by
userspace which justifies _IOC_WRITE flag.  It also writes back to that
structure which justifies _IOC_READ flag.

See NOTEs in include/uapi/asm-generic/ioctl.h for more information.

Fixes: f619147104c8 ("userfaultfd: add UFFDIO_CONTINUE ioctl")
Signed-off-by: Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Dmitry V. Levin <ldv@altlinux.org>
---
 include/uapi/linux/userfaultfd.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Please make sure this patch is merged before v5.13 is released,
otherwise the UAPI bug would have to stay for backwards ABI
compatibility.

diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index bafbeb1a2624..650480f41f1d 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -80,8 +80,8 @@
 				      struct uffdio_zeropage)
 #define UFFDIO_WRITEPROTECT	_IOWR(UFFDIO, _UFFDIO_WRITEPROTECT, \
 				      struct uffdio_writeprotect)
-#define UFFDIO_CONTINUE		_IOR(UFFDIO, _UFFDIO_CONTINUE,	\
-				     struct uffdio_continue)
+#define UFFDIO_CONTINUE		_IOWR(UFFDIO, _UFFDIO_CONTINUE,	\
+				      struct uffdio_continue)
 
 /* read() structure */
 struct uffd_msg {
-- 
glebfm