[PATCH] fuse: Mark fscrypt ioctls as unrestricted

[Chirantan Ekbote <chirantan@chromium.org>]

The definitions for these 2 ioctls have been reversed: "get" is marked
as a write ioctl and "set" is marked as a read ioctl.  Moreover, since
these are now part of the public kernel interface they can never be
fixed because fixing them might break userspace applications compiled
with the older headers.

Since the fuse module strictly enforces the ioctl encodings, it will
reject any attempt by the fuse server to correctly implement these
ioctls.  Instead, check if the process is trying to make one of these
ioctls and mark it unrestricted.  This will allow the server to fix the
encoding by reading/writing the correct data.

Signed-off-by: Chirantan Ekbote <chirantan@chromium.org>
---
 fs/fuse/file.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 9d67b830fb7a2..9b6d993323d53 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -18,6 +18,7 @@
 #include <linux/swap.h>
 #include <linux/falloc.h>
 #include <linux/uio.h>
+#include <linux/fscrypt.h>
 
 static struct page **fuse_pages_alloc(unsigned int npages, gfp_t flags,
 				      struct fuse_page_desc **desc)
@@ -2751,6 +2752,16 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
 
 	fuse_page_descs_length_init(ap.descs, 0, fc->max_pages);
 
+	/*
+	 * These commands are encoded backwards so it is literally impossible
+	 * for a fuse server to implement them. Instead, mark them unrestricted
+	 * so that the server can deal with the broken encoding itself.
+	 */
+	if (cmd == FS_IOC_GET_ENCRYPTION_POLICY ||
+	    cmd == FS_IOC_SET_ENCRYPTION_POLICY) {
+		flags |= FUSE_IOCTL_UNRESTRICTED;
+	}
+
 	/*
 	 * If restricted, initialize IO parameters as encoded in @cmd.
 	 * RETRY from server is not allowed.
-- 
2.26.1.301.g55bc3eb7cb9-goog