[PATCH 1/2] io_uring: fix overflows checks in provide buffers

[Pavel Begunkov <asml.silence@gmail.com>]

Colin reported before possible overflow and sign extension problems in
io_provide_buffers_prep(). As Linus pointed out previous attempt did nothing
useful, see d81269fecb8ce ("io_uring: fix provide_buffers sign extension").

Do that with help of check_<op>_overflow helpers. And fix struct
io_provide_buf::len type, as it doesn't make much sense to keep it
signed.

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>
---
 fs/io_uring.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index e9d60dee075e..b57994443b2c 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -627,7 +627,7 @@ struct io_splice {
 struct io_provide_buf {
 	struct file			*file;
 	__u64				addr;
-	__s32				len;
+	__u32				len;
 	__u32				bgid;
 	__u16				nbufs;
 	__u16				bid;
@@ -3923,7 +3923,7 @@ 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;
+	unsigned long size, tmp_check;
 	struct io_provide_buf *p = &req->pbuf;
 	u64 tmp;
 
@@ -3937,6 +3937,12 @@ static int io_provide_buffers_prep(struct io_kiocb *req,
 	p->addr = READ_ONCE(sqe->addr);
 	p->len = READ_ONCE(sqe->len);
 
+	if (check_mul_overflow((unsigned long)p->len, (unsigned long)p->nbufs,
+				&size))
+		return -EOVERFLOW;
+	if (check_add_overflow((unsigned long)p->addr, size, &tmp_check))
+		return -EOVERFLOW;
+
 	size = (unsigned long)p->len * p->nbufs;
 	if (!access_ok(u64_to_user_ptr(p->addr), size))
 		return -EFAULT;
-- 
2.24.0