io_uring: fix provide_buffers sign extension

stable inclusion
from stable-5.10.27
commit dcf2dfc1614d64bc3366bdeeb302f32bc2050c4a
bugzilla: 51493

--------------------------------

[ Upstream commit d81269fe ]

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: NColin Ian King <colin.king@canonical.com>
Fixes: efe68c1c ("io_uring: validate the full range of provided buffers for access")
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Reviewed-by: NColin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/562376a39509e260d8532186a06226e56eb1f594.1616149233.git.asml.silence@gmail.comSigned-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: N  Weilong Chen <chenweilong@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

fs/io_uring.c

@@ -3996,6 +3996,7 @@ static int io_remove_buffers(struct io_kiocb *req, bool force_nonblock,
 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;
 
@@ -4009,7 +4010,8 @@ 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);