[lttng-dev] [PATCH babeltrace] Fix: Double free in bt_context_remove_trace().

[Julien Desfossez]

On 21/01/13 02:32 PM, Mathieu Desnoyers wrote:
> * Jérémie Galarneau (jeremie.galarneau at efficios.com) wrote:
>> ctf_close_trace was being called twice when calling bt_context_remove_trace thus
>> causing free() to be called on an invalid pointer.
>>
>> Calling bt_context_remove_trace() would call ctf_close_trace() once via the
>> close_handle callback registered on the ctf format struct and a second call would
>> take place from bt_trace_handle_destroy() which is registered as the
>> value_destroy_func on the trace_handles hash table of the current context.
>>
>> The first explicit call to handle->format->close_trace is unnecessary.
>>
>> The crash is reproducible by invoking the tests-python.py script.
> 
> I think we should leave the close_trace calls in both locations, but set
> handle->td to -1 when we close it, and test for negative handle ID
> before doing the close.

I agree, we need the two calls to close, one is called when we remove a
trace manually and the other one is called when we destroy the context.
Setting and testing the td to -1 will solve the problem and will avoid
calling close_trace at all if not needed.

Thanks,

Julien

> 
> Thanks,
> 
> Mathieu
> 
>>
>> Signed-off-by: Jérémie Galarneau <jeremie.galarneau at efficios.com>
>> ---
>>  lib/context.c      | 8 +-------
>>  lib/trace-handle.c | 5 ++++-
>>  2 files changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/lib/context.c b/lib/context.c
>> index 5516e49..05fb994 100644
>> --- a/lib/context.c
>> +++ b/lib/context.c
>> @@ -156,7 +156,6 @@ end:
>>  int bt_context_remove_trace(struct bt_context *ctx, int handle_id)
>>  {
>>  	struct bt_trace_handle *handle;
>> -	int ret;
>>  
>>  	if (!ctx)
>>  		return -EINVAL;
>> @@ -168,12 +167,7 @@ int bt_context_remove_trace(struct bt_context *ctx, int handle_id)
>>  
>>  	/* Remove from containers */
>>  	trace_collection_remove(ctx->tc, handle->td);
>> -	/* Close the trace */
>> -	ret = handle->format->close_trace(handle->td);
>> -	if (ret) {
>> -		fprintf(stderr, "Error in close_trace callback\n");
>> -		return ret;
>> -	}
>> +
>>  	/* Remove and free the handle */
>>  	g_hash_table_remove(ctx->trace_handles,
>>  			(gpointer) (unsigned long) handle_id);
>> diff --git a/lib/trace-handle.c b/lib/trace-handle.c
>> index 0da565b..17a6e0d 100644
>> --- a/lib/trace-handle.c
>> +++ b/lib/trace-handle.c
>> @@ -49,7 +49,10 @@ struct bt_trace_handle *bt_trace_handle_create(struct bt_context *ctx)
>>  
>>  void bt_trace_handle_destroy(struct bt_trace_handle *th)
>>  {
>> -	th->format->close_trace(th->td);
>> +	if (th->format->close_trace(th->td)) {
>> +		fprintf(stderr, "Error in close_trace callback\n");
>> +	}
>> +
>>  	g_free(th);
>>  }
>>  
>> -- 
>> 1.8.1.1
>>
>>
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>