pespin has submitted this change. (
https://gerrit.osmocom.org/c/osmo-bts/+/32552?usp=email )
Change subject: trx_if: Allow calling trx_if_flush/close from within TRXC
callback (v2)
......................................................................
trx_if: Allow calling trx_if_flush/close from within TRXC callback (v2)
- If the llist is flushed during rx rsp callback, when the flow is
returned to trx_ctrl_read_cb() it would access tcm which was in the
llist and end up in use-after-free.
- We need to store state on whether code path is inside the read_cb in
order to:
-- Delay transmission of new message if callback calls trx_if_flush()
followed by trx_ctrl_send(), since the trx_ctrl_send() at the end of
trx_ctrl_read_cb would retransmit it again immediatelly.
-- Avoid accessing tcm pointer if the callback called trx_if_flush(),
since it has been freed.
Related: OS#6020
Change-Id: Ibdffa4644aa3a7d219452644d3e74b411734f1df
---
M src/osmo-bts-trx/l1_if.h
M src/osmo-bts-trx/trx_if.c
2 files changed, 52 insertions(+), 7 deletions(-)
Approvals:
daniel: Looks good to me, but someone else must approve
Jenkins Builder: Verified
pespin: Looks good to me, approved
diff --git a/src/osmo-bts-trx/l1_if.h b/src/osmo-bts-trx/l1_if.h
index 18d84c2..84fd4b5 100644
--- a/src/osmo-bts-trx/l1_if.h
+++ b/src/osmo-bts-trx/l1_if.h
@@ -120,6 +120,10 @@
struct llist_head trx_ctrl_list;
/* Latest RSPed cmd, used to catch duplicate RSPs from sent
retransmissions */
struct trx_ctrl_msg *last_acked;
+ /* Whether the code path is in the middle of handling a received
message. */
+ bool in_trx_ctrl_read_cb;
+ /* Whether the l1h->trx_ctrl_list was flushed by the callback handling
a received message */
+ bool flushed_while_in_trx_ctrl_read_cb;
//struct gsm_bts_trx *trx;
struct phy_instance *phy_inst;
diff --git a/src/osmo-bts-trx/trx_if.c b/src/osmo-bts-trx/trx_if.c
index 3f9fc04..89078a3 100644
--- a/src/osmo-bts-trx/trx_if.c
+++ b/src/osmo-bts-trx/trx_if.c
@@ -269,8 +269,10 @@
tcm->cmd, tcm->params_len ? " " : "", tcm->params);
llist_add_tail(&tcm->list, &l1h->trx_ctrl_list);
- /* send message, if we didn't already have pending messages */
- if (prev == NULL)
+ /* send message, if we didn't already have pending messages.
+ * If we are in the rx_rsp callback code path, skip sending, the
+ * callback will do so when returning to it. */
+ if (prev == NULL && !l1h->in_trx_ctrl_read_cb)
trx_ctrl_send(l1h);
return 0;
@@ -673,6 +675,7 @@
struct trx_ctrl_rsp rsp;
int len, rc;
struct trx_ctrl_msg *tcm;
+ bool flushed;
len = recv(ofd->fd, buf, sizeof(buf) - 1, 0);
if (len <= 0)
@@ -722,21 +725,34 @@
rsp.cb = tcm->cb;
/* check for response code */
+ l1h->in_trx_ctrl_read_cb = true;
rc = trx_ctrl_rx_rsp(l1h, &rsp, tcm);
+ /* Reset state: */
+ flushed = l1h->flushed_while_in_trx_ctrl_read_cb;
+ l1h->flushed_while_in_trx_ctrl_read_cb = false;
+ l1h->in_trx_ctrl_read_cb = false;
+
if (rc == -EINVAL)
goto rsp_error;
/* re-schedule last cmd in rc seconds time */
if (rc > 0) {
- osmo_timer_schedule(&l1h->trx_ctrl_timer, rc, 0);
+ /* The queue may have been flushed in the trx_ctrl_rx_rsp(): */
+ if (!llist_empty(&l1h->trx_ctrl_list))
+ osmo_timer_schedule(&l1h->trx_ctrl_timer, rc, 0);
return 0;
}
- /* remove command from list, save it to last_acked and removed previous
last_acked */
- llist_del(&tcm->list);
- talloc_free(l1h->last_acked);
- l1h->last_acked = tcm;
+ if (!flushed) {
+ /* Remove command from list, save it to last_acked and removed
+ * previous last_acked */
+ llist_del(&tcm->list);
+ talloc_free(l1h->last_acked);
+ l1h->last_acked = tcm;
+ } /* else: tcm was freed by trx_if_flush(), do not access it. */
+
+ /* Send next message waiting in the list: */
trx_ctrl_send(l1h);
return 0;
@@ -1224,6 +1240,10 @@
/* Tx queue is now empty, so there's no point in keeping the retrans
timer armed: */
osmo_timer_del(&l1h->trx_ctrl_timer);
+
+ /* If we are in read_cb, signal to the returning code path that we
freed the list. */
+ if (l1h->in_trx_ctrl_read_cb)
+ l1h->flushed_while_in_trx_ctrl_read_cb = true;
}
/*! close the TRX for given handle (data + control socket) */
--
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Gerrit-Project: osmo-bts
Gerrit-Branch: master
Gerrit-Change-Id: Ibdffa4644aa3a7d219452644d3e74b411734f1df
Gerrit-Change-Number: 32552
Gerrit-PatchSet: 7
Gerrit-Owner: fixeria <vyanits...@sysmocom.de>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: daniel <dwillm...@sysmocom.de>
Gerrit-Reviewer: fixeria <axilira...@gmail.com>
Gerrit-Reviewer: fixeria <vyanits...@sysmocom.de>
Gerrit-Reviewer: laforge <lafo...@osmocom.org>
Gerrit-Reviewer: pespin <pes...@sysmocom.de>
Gerrit-MessageType: merged
