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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
This commit is contained in:
Pau Espin 2023-10-25 14:49:11 +02:00
parent 14091bd2e9
commit 2217096be6
2 changed files with 31 additions and 7 deletions
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4
src/osmo-bts-trx/l1_if.h
View File

@ -120,6 +120,10 @@ struct trx_l1h {
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;

34
src/osmo-bts-trx/trx_if.c
View File

@ -269,8 +269,10 @@ static int trx_ctrl_cmd_cb(struct trx_l1h *l1h, int critical, void *cb, const ch
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 @@ static int trx_ctrl_read_cb(struct osmo_fd *ofd, unsigned int what)
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 @@ static int trx_ctrl_read_cb(struct osmo_fd *ofd, unsigned int what)
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 @@ void trx_if_flush(struct trx_l1h *l1h)
/* 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) */