res_pjsip_t38.c: Fix deadlock in T.38 framehook.

A deadlock can happen between a channel lock and a pjsip session media
container lock.  One thread is processing a reINVITE's SDP and walking
through the session's media container when it waits for the channel lock
to put the determined format capabilities onto the channel.  The other
thread is writing a frame to the channel and processing the T.38 frame
hook.  The T.38 frame hook then waits for the pjsip session's media
container lock.  The two threads are now deadlocked.

* Made the T.38 frame hook release the channel lock before searching the
session's media container.  This fix has been done to several other
frame hooks to fix deadlocks.

ASTERISK-26974 #close

Change-Id: Ie984a76ce00bef6ec9aa239010e51e8dd74c8186

diff --git a/res/res_pjsip_t38.c b/res/res_pjsip_t38.c
index 04774190ef4564f51613534fcecdd646109056c7..0ce6474e3a3156c1a036a95aa2573b9f95c40628 100644 (file)
--- a/res/res_pjsip_t38.c
+++ b/res/res_pjsip_t38.c
@@ -400,7 +400,8 @@ static int t38_interpret_parameters(void *obj)
 }
 
 /*! \brief Frame hook callback for writing */
-static struct ast_frame *t38_framehook_write(struct ast_sip_session *session, struct ast_frame *f)
+static struct ast_frame *t38_framehook_write(struct ast_channel *chan,
+       struct ast_sip_session *session, struct ast_frame *f)
 {
        if (f->frametype == AST_FRAME_CONTROL && f->subclass.integer == AST_CONTROL_T38_PARAMETERS &&
                session->endpoint->media.t38.enabled) {
@@ -414,27 +415,36 @@ static struct ast_frame *t38_framehook_write(struct ast_sip_session *session, st
                        ao2_ref(data, -1);
                }
        } else if (f->frametype == AST_FRAME_MODEM) {
-               RAII_VAR(struct ast_sip_session_media *, session_media, NULL, ao2_cleanup);
+               struct ast_sip_session_media *session_media;
 
-               if ((session_media = ao2_find(session->media, "image", OBJ_KEY)) &&
-                       session_media->udptl) {
+               /* Avoid deadlock between chan and the session->media container lock */
+               ast_channel_unlock(chan);
+               session_media = ao2_find(session->media, "image", OBJ_SEARCH_KEY);
+               ast_channel_lock(chan);
+               if (session_media && session_media->udptl) {
                        ast_udptl_write(session_media->udptl, f);
                }
+               ao2_cleanup(session_media);
        }
 
        return f;
 }
 
 /*! \brief Frame hook callback for reading */
-static struct ast_frame *t38_framehook_read(struct ast_sip_session *session, struct ast_frame *f)
+static struct ast_frame *t38_framehook_read(struct ast_channel *chan,
+       struct ast_sip_session *session, struct ast_frame *f)
 {
        if (ast_channel_fdno(session->channel) == 5) {
-               RAII_VAR(struct ast_sip_session_media *, session_media, NULL, ao2_cleanup);
+               struct ast_sip_session_media *session_media;
 
-               if ((session_media = ao2_find(session->media, "image", OBJ_KEY)) &&
-                       session_media->udptl) {
+               /* Avoid deadlock between chan and the session->media container lock */
+               ast_channel_unlock(chan);
+               session_media = ao2_find(session->media, "image", OBJ_SEARCH_KEY);
+               ast_channel_lock(chan);
+               if (session_media && session_media->udptl) {
                        f = ast_udptl_read(session_media->udptl);
                }
+               ao2_cleanup(session_media);
        }
 
        return f;
@@ -447,9 +457,9 @@ static struct ast_frame *t38_framehook(struct ast_channel *chan, struct ast_fram
        struct ast_sip_channel_pvt *channel = ast_channel_tech_pvt(chan);
 
        if (event == AST_FRAMEHOOK_EVENT_READ) {
-               f = t38_framehook_read(channel->session, f);
+               f = t38_framehook_read(chan, channel->session, f);
        } else if (event == AST_FRAMEHOOK_EVENT_WRITE) {
-               f = t38_framehook_write(channel->session, f);
+               f = t38_framehook_write(chan, channel->session, f);
        }
 
        return f;