[PATCH] fuse: Apply flags2 only when userspace set the FUSE_INIT_EXT flag

[Bernd Schubert <bschubert@ddn.com>]

This is just a safety precaution to avoid checking flags
on memory that was initialized on the user space side.
libfuse zeroes struct fuse_init_out outarg, but this is not
guranteed to be done in all implementations. Better is to
act on flags and to only apply flags2 when FUSE_INIT_EXT
is set.

There is a risk with this change, though - it might break existing
user space libraries, which are already using flags2 without
setting FUSE_INIT_EXT.

The corresponding libfuse patch is here
https://github.com/libfuse/libfuse/pull/662


Signed-off-by: Bernd Schubert <bschubert@ddn.com>
---
 fs/fuse/inode.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 9ee36aa73251..8115a06d5fbb 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1115,7 +1115,10 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
 		process_init_limits(fc, arg);
 
 		if (arg->minor >= 6) {
-			u64 flags = arg->flags | (u64) arg->flags2 << 32;
+			u64 flags = arg->flags;
+
+			if (flags & FUSE_INIT_EXT)
+				flags |= (u64) arg->flags2 << 32;
 
 			ra_pages = arg->max_readahead / PAGE_SIZE;
 			if (flags & FUSE_ASYNC_READ)