4 is the latest approved patch-set.
No files were changed between the latest approved patch-set and the submitted one.


osmo_io_uring: Cancel pending request, free msghdr on completion

There is always a completion after cancelling a uring request.

Because uring requests use msghdr pointer as user data, we cannot just
free the msghdr after cancelling. Upon completion (received after
cancelling), the user data still points to the msghdr. To prevent a
use-after-free bug, msghdr is not freed, but detached from iofd
instance. Then upon completion, the msghdr (if it was detached from
iofd) is freed.

Additionally it is not required to keep IOFD_FLAG_IN_CALLBACK set
anymore, if there is a msghdr attached to iofd. As described above,
all msghdr get detached, if iofd is freed (uring request get cancelled)
during callback.

Related: OS#5751
Change-Id: Ic253f085dd6362db85f029f46350951472210a02
---
M src/core/osmo_io_uring.c
1 file changed, 43 insertions(+), 4 deletions(-)

diff --git a/src/core/osmo_io_uring.c b/src/core/osmo_io_uring.c
index af1c790..3812b50 100644
--- a/src/core/osmo_io_uring.c
+++ b/src/core/osmo_io_uring.c
@@ -230,8 +230,7 @@
 		OSMO_ASSERT(0)
 	}
 
-	if (!iofd->u.uring.read_msghdr && !iofd->u.uring.write_msghdr)
-		IOFD_FLAG_UNSET(iofd, IOFD_FLAG_IN_CALLBACK);
+	IOFD_FLAG_UNSET(iofd, IOFD_FLAG_IN_CALLBACK);
 
 	if (IOFD_FLAG_ISSET(iofd, IOFD_FLAG_TO_FREE) && !iofd->u.uring.read_msghdr && !iofd->u.uring.write_msghdr)
 		talloc_free(iofd);
@@ -252,6 +251,11 @@
 			io_uring_cqe_seen(ring, cqe);
 			continue;
 		}
+		if (!msghdr->iofd) {
+			io_uring_cqe_seen(ring, cqe);
+			iofd_msghdr_free(msghdr);
+			continue;
+		}
 
 		rc = cqe->res;
 		/* Hand the entry back to the kernel before */
@@ -307,20 +311,31 @@
 static int iofd_uring_unregister(struct osmo_io_fd *iofd)
 {
 	struct io_uring_sqe *sqe;
+	struct iofd_msghdr *msghdr;
+
 	if (iofd->u.uring.read_msghdr) {
+		msghdr = iofd->u.uring.read_msghdr;
 		sqe = io_uring_get_sqe(&g_ring.ring);
 		OSMO_ASSERT(sqe != NULL);
 		io_uring_sqe_set_data(sqe, NULL);
 		LOGPIO(iofd, LOGL_DEBUG, "Cancelling read\n");
-		io_uring_prep_cancel(sqe, iofd->u.uring.read_msghdr, 0);
+		iofd->u.uring.read_msghdr = NULL;
+		talloc_steal(OTC_GLOBAL, msghdr);
+		msghdr->iofd = NULL;
+		io_uring_prep_cancel(sqe, msghdr, 0);
 	}
 
 	if (iofd->u.uring.write_msghdr) {
+		msghdr = iofd->u.uring.write_msghdr;
 		sqe = io_uring_get_sqe(&g_ring.ring);
 		OSMO_ASSERT(sqe != NULL);
 		io_uring_sqe_set_data(sqe, NULL);
 		LOGPIO(iofd, LOGL_DEBUG, "Cancelling write\n");
-		io_uring_prep_cancel(sqe, iofd->u.uring.write_msghdr, 0);
+		iofd->u.uring.write_msghdr = NULL;
+		talloc_steal(OTC_GLOBAL, msghdr);
+		msgb_free(msghdr->msg);
+		msghdr->iofd = NULL;
+		io_uring_prep_cancel(sqe, msghdr, 0);
 	}
 	io_uring_submit(&g_ring.ring);
 

