io_uring: truncate lengths larger than MAX_RW_COUNT on provide buffers

commit d1f82808877bb10d3deee7cf3374a4eb3fb582db upstream.

Read and write operations are capped to MAX_RW_COUNT. Some read ops rely on
that limit, and that is not guaranteed by the IORING_OP_PROVIDE_BUFFERS.

Truncate those lengths when doing io_add_buffers, so buffer addresses still
use the uncapped length.

Also, take the chance and change struct io_buffer len member to __u32, so
it matches struct io_provide_buffer len member.

This fixes CVE-2021-3491, also reported as ZDI-CAN-13546.

Fixes: ddf0322db79c ("io_uring: add IORING_OP_PROVIDE_BUFFERS")
Reported-by: Billy Jheng Bing-Jhong (@st424204)
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index dc1b0f6fd49b58009885dc502f283d5a655caaff..55e214defb42f31981a3fe0cff4380760cc89552 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -222,7 +222,7 @@ struct fixed_file_data {
 struct io_buffer {
        struct list_head list;
        __u64 addr;
-       __s32 len;
+       __u32 len;
        __u16 bid;
 };
 
@@ -4034,7 +4034,7 @@ static int io_add_buffers(struct io_provide_buf *pbuf, struct io_buffer **head)
                        break;
 
                buf->addr = addr;
-               buf->len = pbuf->len;
+               buf->len = min_t(__u32, pbuf->len, MAX_RW_COUNT);
                buf->bid = bid;
                addr += pbuf->len;
                bid++;