io_uring/net: fix UAF in io_sendrecv_fail()

We should not assume anything about ->free_iov just from
REQ_F_ASYNC_DATA but rather rely on REQ_F_NEED_CLEANUP, as we may
allocate ->async_data but failed init would leave the field in not
consistent state. The easiest solution is to remove removing
REQ_F_NEED_CLEANUP and so ->async_data dealloc from io_sendrecv_fail()
and let io_send_zc_cleanup() do the job. The catch here is that we also
need to prevent double notif flushing, just test it for NULL and zero
where it's needed.

BUG: KASAN: use-after-free in io_sendrecv_fail+0x3b0/0x3e0 io_uring/net.c:1221
Write of size 8 at addr ffff8880771b4080 by task syz-executor.3/30199

CPU: 1 PID: 30199 Comm: syz-executor.3 Not tainted 6.0.0-rc6-next-20220923-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:284 [inline]
 print_report+0x15e/0x45d mm/kasan/report.c:395
 kasan_report+0xbb/0x1f0 mm/kasan/report.c:495
 io_sendrecv_fail+0x3b0/0x3e0 io_uring/net.c:1221
 io_req_complete_failed+0x155/0x1b0 io_uring/io_uring.c:873
 io_drain_req io_uring/io_uring.c:1648 [inline]
 io_queue_sqe_fallback.cold+0x29f/0x788 io_uring/io_uring.c:1931
 io_submit_sqe io_uring/io_uring.c:2160 [inline]
 io_submit_sqes+0x1180/0x1df0 io_uring/io_uring.c:2276
 __do_sys_io_uring_enter+0xac6/0x2410 io_uring/io_uring.c:3216
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: c4c0009e ("io_uring/net: combine fail handlers")
Reported-by: syzbot+4c597a574a3f5a251bda@syzkaller.appspotmail.com
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/23ab8346e407ea50b1198a172c8a97e1cf22915b.1663945875.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/net.c

@@ -915,9 +915,11 @@ void io_send_zc_cleanup(struct io_kiocb *req)
 		io = req->async_data;
 		kfree(io->free_iov);
 	}
-	zc->notif->flags |= REQ_F_CQE_SKIP;
-	io_notif_flush(zc->notif);
-	zc->notif = NULL;
+	if (zc->notif) {
+		zc->notif->flags |= REQ_F_CQE_SKIP;
+		io_notif_flush(zc->notif);
+		zc->notif = NULL;
+	}
 }
 
 int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
@@ -1202,7 +1204,6 @@ int io_sendmsg_zc(struct io_kiocb *req, unsigned int issue_flags)
 void io_sendrecv_fail(struct io_kiocb *req)
 {
 	struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg);
-	struct io_async_msghdr *io;
 	int res = req->cqe.res;
 
 	if (req->flags & REQ_F_PARTIAL_IO)
@@ -1215,12 +1216,6 @@ void io_sendrecv_fail(struct io_kiocb *req)
 		io_notif_flush(sr->notif);
 		sr->notif = NULL;
 	}
-	if (req_has_async_data(req)) {
-		io = req->async_data;
-		kfree(io->free_iov);
-		io->free_iov = NULL;
-	}
-	req->flags &= ~REQ_F_NEED_CLEANUP;
 	io_req_set_res(req, res, req->cqe.flags);
 }