Merged revisions 219139 via svnmerge from

https://origsvn.digium.com/svn/asterisk/trunk

................
  r219139 | mnicholson | 2009-09-17 10:18:01 -0500 (Thu, 17 Sep 2009) | 17 lines
  
  Merged revisions 219136 via svnmerge from 
  https://origsvn.digium.com/svn/asterisk/branches/1.4
  
  ........
    r219136 | mnicholson | 2009-09-17 09:58:39 -0500 (Thu, 17 Sep 2009) | 10 lines
    
    Prevent a potential race condition and crash when hanging up a channel by removing the channel from the channel list before begining channel tear down.
    
    This fix may potentially cause problems with CDR backends that access the channel a CDR is associated with via the channel list.  This fix makes the channel unavabile at the time when the CDR backend is invoked.  This has been documented in include/asterisk/cdr.h.
    
    (closes issue #15316)
    Reported by: vmarrone
    Tested by: mnicholson
    
    Review: https://reviewboard.asterisk.org/r/362/
  ........
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git-svn-id: http://svn.digium.com/svn/asterisk/branches/1.6.2@219194 f38db490-d61c-443f-a65b-d21fe96a405b

3 files changed, 33 insertions, 8 deletions

diff --git a/include/asterisk/cdr.h b/include/asterisk/cdr.h
index 1f71039eb..1e3a36d26 100644
--- a/include/asterisk/cdr.h
+++ b/include/asterisk/cdr.h
@@ -120,6 +120,12 @@ int ast_cdr_serialize_variables(struct ast_cdr *cdr, struct ast_str **buf, char
 void ast_cdr_free_vars(struct ast_cdr *cdr, int recur);
 int ast_cdr_copy_vars(struct ast_cdr *to_cdr, struct ast_cdr *from_cdr);
 
+/*!
+ * \brief CDR backend callback
+ * \warning CDR backends should NOT attempt to access the channel associated
+ * with a CDR record.  This channel is not guaranteed to exist when the CDR
+ * backend is invoked.
+ */
 typedef int (*ast_cdrbe)(struct ast_cdr *cdr);
 
 /*! \brief Return TRUE if CDR subsystem is enabled */
diff --git a/include/asterisk/channel.h b/include/asterisk/channel.h
index 1156b3270..f0ff3d09c 100644
--- a/include/asterisk/channel.h
+++ b/include/asterisk/channel.h
@@ -563,6 +563,8 @@ enum {
 	 *  bridge terminates, this will allow the hangup in the pbx loop to be run instead.
 	 *  */
 	AST_FLAG_BRIDGE_HANGUP_DONT = (1 << 18),
+	/*! This flag indicates whether the channel is in the channel list or not. */
+	AST_FLAG_IN_CHANNEL_LIST = (1 << 19),
 };
 
 /*! \brief ast_bridge_config flags */
diff --git a/main/channel.c b/main/channel.c
index dd92aca92..7b16436c9 100644
--- a/main/channel.c
+++ b/main/channel.c
@@ -931,6 +931,8 @@ alertpipe_failed:
 
 	tmp->tech = &null_tech;
 
+	ast_set_flag(tmp, AST_FLAG_IN_CHANNEL_LIST);
+
 	AST_RWLIST_WRLOCK(&channels);
 	AST_RWLIST_INSERT_HEAD(&channels, tmp, chan_list);
 	AST_RWLIST_UNLOCK(&channels);
@@ -1374,17 +1376,21 @@ void ast_channel_free(struct ast_channel *chan)
 	struct varshead *headp;
 	struct ast_datastore *datastore = NULL;
 	char name[AST_CHANNEL_NAME], *dashptr;
+	int inlist;
 	
 	headp=&chan->varshead;
 	
-	AST_RWLIST_WRLOCK(&channels);
-	if (!AST_RWLIST_REMOVE(&channels, chan, chan_list)) {
-		ast_log(LOG_ERROR, "Unable to find channel in list to free. Assuming it has already been done.\n");
+	inlist = ast_test_flag(chan, AST_FLAG_IN_CHANNEL_LIST);
+	if (inlist) {
+		AST_RWLIST_WRLOCK(&channels);
+		if (!AST_RWLIST_REMOVE(&channels, chan, chan_list)) {
+			ast_debug(1, "Unable to find channel in list to free. Assuming it has already been done.\n");
+		}
+		/* Lock and unlock the channel just to be sure nobody has it locked still
+		   due to a reference retrieved from the channel list. */
+		ast_channel_lock(chan);
+		ast_channel_unlock(chan);
 	}
-	/* Lock and unlock the channel just to be sure nobody has it locked still
-	   due to a reference retrieved from the channel list. */
-	ast_channel_lock(chan);
-	ast_channel_unlock(chan);
 
 	/* Get rid of each of the data stores on the channel */
 	while ((datastore = AST_LIST_REMOVE_HEAD(&chan->datastores, entry)))
@@ -1467,7 +1473,8 @@ void ast_channel_free(struct ast_channel *chan)
 
 	ast_string_field_free_memory(chan);
 	ast_free(chan);
-	AST_RWLIST_UNLOCK(&channels);
+	if (inlist)
+		AST_RWLIST_UNLOCK(&channels);
 
 	/* Queue an unknown state, because, while we know that this particular
 	 * instance is dead, we don't know the state of all other possible
@@ -1690,6 +1697,16 @@ int ast_hangup(struct ast_channel *chan)
 		ast_channel_unlock(chan);
 		return 0;
 	}
+	ast_channel_unlock(chan);
+
+	AST_RWLIST_WRLOCK(&channels);
+	if (!AST_RWLIST_REMOVE(&channels, chan, chan_list)) {
+		ast_log(LOG_ERROR, "Unable to find channel in list to free. Assuming it has already been done.\n");
+	}
+	ast_clear_flag(chan, AST_FLAG_IN_CHANNEL_LIST);
+	AST_RWLIST_UNLOCK(&channels);
+
+	ast_channel_lock(chan);
 	free_translation(chan);
 	/* Close audio stream */
 	if (chan->stream) {