[SRU H/I/OEM-5.10 1/1] io_uring: ensure symmetry in handling iter types in loop_rw_iter()

[Thadeu Lima de Souza Cascardo]

From: Jens Axboe <axboe at kernel.dk>

When setting up the next segment, we check what type the iter is and
handle it accordingly. However, when incrementing and processed amount
we do not, and both iter advance and addr/len are adjusted, regardless
of type. Split the increment side just like we do on the setup side.

Fixes: 4017eb91a9e7 ("io_uring: make loop_rw_iter() use original user supplied pointers")
Cc: stable at vger.kernel.org
Reported-by: Valentina Palmiotti <vpalmiotti at gmail.com>
Reviewed-by: Pavel Begunkov <asml.silence at gmail.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
(cherry picked from commit 16c8d2df7ec0eed31b7d3b61cb13206a7fb930cc)
CVE-2021-41073
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 fs/io_uring.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index e1e1acc4be15..b4e9b68fe196 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3309,12 +3309,15 @@ static ssize_t loop_rw_iter(int rw, struct io_kiocb *req, struct iov_iter *iter)
 				ret = nr;
 			break;
 		}
+		if (!iov_iter_is_bvec(iter)) {
+			iov_iter_advance(iter, nr);
+		} else {
+			req->rw.len -= nr;
+			req->rw.addr += nr;
+		}
 		ret += nr;
 		if (nr != iovec.iov_len)
 			break;
-		req->rw.len -= nr;
-		req->rw.addr += nr;
-		iov_iter_advance(iter, nr);
 	}
 
 	return ret;
-- 
2.30.2