io_uring: ensure openat sets O_LARGEFILE if needed

OPENAT2 correctly sets O_LARGEFILE if it has to, but that escaped the
OPENAT opcode. Dmitry reports that his test case that compares openat()
and IORING_OP_OPENAT sees failures on large files:

*** sync openat
openat succeeded
sync write at offset 0
write succeeded
sync write at offset 4294967296
write succeeded

*** sync openat
openat succeeded
io_uring write at offset 0
write succeeded
io_uring write at offset 4294967296
write succeeded

*** io_uring openat
openat succeeded
sync write at offset 0
write succeeded
sync write at offset 4294967296
write failed: File too large

*** io_uring openat
openat succeeded
io_uring write at offset 0
write succeeded
io_uring write at offset 4294967296
write failed: File too large

Ensure we set O_LARGEFILE, if force_o_largefile() is true.

Cc: stable@vger.kernel.org # v5.6
Fixes: 15b71abe ("io_uring: add support for IORING_OP_OPENAT")
Reported-by: Dmitry Kadashev <dkadashev@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2957,6 +2957,8 @@ static int io_openat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	req->open.how.mode = READ_ONCE(sqe->len);
 	fname = u64_to_user_ptr(READ_ONCE(sqe->addr));
 	req->open.how.flags = READ_ONCE(sqe->open_flags);
+	if (force_o_largefile())
+		req->open.how.flags |= O_LARGEFILE;
 
 	req->open.filename = getname(fname);
 	if (IS_ERR(req->open.filename)) {