io_uring: fix provide_buffers sign extension

io_provide_buffers_prep()'s "p->len * p->nbufs" to sign extension
problems. Not a huge problem as it's only used for access_ok() and
increases the checked length, but better to keep typing right.

Reported-by: Colin Ian King <colin.king@canonical.com>
Fixes: efe68c1ca8f49 ("io_uring: validate the full range of provided buffers for access")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/562376a39509e260d8532186a06226e56eb1f594.1616149233.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index a664b44a5a9452056caab8cbec9ef8c0f6fcd1ea..f3ae83a2d7bc04c0ee2c6c2d4593184265f5d6c8 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3977,6 +3977,7 @@ static int io_remove_buffers(struct io_kiocb *req, unsigned int issue_flags)
 static int io_provide_buffers_prep(struct io_kiocb *req,
                                   const struct io_uring_sqe *sqe)
 {
+       unsigned long size;
        struct io_provide_buf *p = &req->pbuf;
        u64 tmp;
 
@@ -3990,7 +3991,8 @@ static int io_provide_buffers_prep(struct io_kiocb *req,
        p->addr = READ_ONCE(sqe->addr);
        p->len = READ_ONCE(sqe->len);
 
-       if (!access_ok(u64_to_user_ptr(p->addr), (p->len * p->nbufs)))
+       size = (unsigned long)p->len * p->nbufs;
+       if (!access_ok(u64_to_user_ptr(p->addr), size))
                return -EFAULT;
 
        p->bgid = READ_ONCE(sqe->buf_group);