osmo_io_uring: Detach msghdr from iofd before calling iofd_handle_send_completion()
msghdr must be detached, because subsequent callback at
iofd_handle_send_completion() may destroy the iofd (which in turn
frees this msghdr, if still attached) and frees the msghdr, causing a
double free.
Related: OS#5751
Change-Id: Ia349f73de2145fa360b20dd40deb73a8ffc71f07
diff --git a/src/core/osmo_io_uring.c b/src/core/osmo_io_uring.c
index 3812b50..cb636da 100644
--- a/src/core/osmo_io_uring.c
+++ b/src/core/osmo_io_uring.c
@@ -195,6 +195,15 @@
{
struct osmo_io_fd *iofd = msghdr->iofd;
+ /* Detach msghdr from iofd. It might get freed here or it is freed during iofd_handle_send_completion().
+ * If there is pending data to send, iofd_uring_submit_tx() will attach it again.
+ * iofd_handle_send_completion() will invoke a callback function to signal the possibility of write/send.
+ * This callback function might close iofd, leading to the potential freeing of iofd->u.uring.write_msghdr if
+ * still attached. Since iofd_handle_send_completion() frees msghdr at the end of the function, detaching
+ * msghdr here prevents a double-free bug. */
+ if (iofd->u.uring.write_msghdr == msghdr)
+ iofd->u.uring.write_msghdr = NULL;
+
if (OSMO_UNLIKELY(IOFD_FLAG_ISSET(iofd, IOFD_FLAG_CLOSED))) {
msgb_free(msghdr->msg);
iofd_msghdr_free(msghdr);
@@ -202,7 +211,6 @@
iofd_handle_send_completion(iofd, rc, msghdr);
}
- iofd->u.uring.write_msghdr = NULL;
/* submit the next to-be-transmitted message for this file descriptor */
if (iofd->u.uring.write_enabled && !IOFD_FLAG_ISSET(iofd, IOFD_FLAG_CLOSED))
iofd_uring_submit_tx(iofd);