[PATCH 5.10 200/221] io_uring: fix provide_buffers sign extension

[Greg Kroah-Hartman]

From: Pavel Begunkov <asml.silence@xxxxxxxxx>

[ Upstream commit d81269fecb8ce16eb07efafc9ff5520b2a31c486 ]

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@xxxxxxxxxxxxx>
Fixes: efe68c1ca8f49 ("io_uring: validate the full range of provided buffers for access")
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
Reviewed-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/562376a39509e260d8532186a06226e56eb1f594.1616149233.git.asml.silence@xxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/io_uring.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 06e9c2181995..dde290eb7dd0 100644
--- a/fs/io_uring.c
+++ b/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);
-- 
2.30.1