Re: [Qemu-devel] [PATCH] qmp: Fix memory leak in migrate_params_test_apply

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Ying Fang (fangying1@huawei.com) wrote:
> Address Sanitizer shows memory leak in migrate_params_test_apply
> migration/migration.c:1253 and the stack is as bellow:
> 
> Direct leak of 45 byte(s) in 9 object(s) allocated from:
>     #0 0xffffbd7fc1db in __interceptor_malloc (/lib64/libasan.so.4+0xd31db)
>     #1 0xffffbd514163 in g_malloc (/lib64/libglib-2.0.so.0+0x57163)
>     #2 0xffffbd52f43b in g_strdup (/lib64/libglib-2.0.so.0+0x7243b)
>     #3 0xaaaadfa4d623 in migrate_params_test_apply migration/migration.c:1253
>     #4 0xaaaadfa4d623 in qmp_migrate_set_parameters migration/migration.c:1422
>     #5 0xaaaadfa963f3 in hmp_migrate_set_parameter monitor/hmp-cmds.c:1867
>     #6 0xaaaadfa8afe3 in handle_hmp_command monitor/hmp.c:1082
>     #7 0xaaaadf479c57 in qmp_human_monitor_command monitor/misc.c:140
>     #8 0xaaaadfadf87b in qmp_marshal_human_monitor_command qapi/qapi-commands-misc.c:1024
>     #9 0xaaaadfc7797b in do_qmp_dispatch qapi/qmp-dispatch.c:131
>     #10 0xaaaadfc7797b in qmp_dispatch qapi/qmp-dispatch.c:174
>     #11 0xaaaadfa84fff in monitor_qmp_dispatch monitor/qmp.c:120
>     #12 0xaaaadfa85bbf in monitor_qmp_bh_dispatcher monitor/qmp.c:209
>     #13 0xaaaadfd2228f in aio_bh_call util/async.c:89
>     #14 0xaaaadfd2228f in aio_bh_poll util/async.c:117
>     #15 0xaaaadfd29bc3 in aio_dispatch util/aio-posix.c:459
>     #16 0xaaaadfd21ff7 in aio_ctx_dispatch util/async.c:260
>     #17 0xffffbd50e2f7 in g_main_context_dispatch (/lib64/libglib-2.0.so.0+0x512f7)
>     #18 0xaaaadfd278d7 in glib_pollfds_poll util/main-loop.c:218
>     #19 0xaaaadfd278d7 in os_host_main_loop_wait util/main-loop.c:241
>     #20 0xaaaadfd278d7 in main_loop_wait util/main-loop.c:517
>     #21 0xaaaadf67b5e7 in main_loop vl.c:1806
>     #22 0xaaaadf15d453 in main vl.c:4488
> 
> Cc: zhanghailiang <zhang.zhanghailiang@huawei.com>
> Signed-off-by: Ying Fang <fangying1@huawei.com>
> ---
>  migration/migration.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 8b9f2fe30a..05e44ff7cc 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1250,11 +1250,17 @@ static void migrate_params_test_apply(MigrateSetParameters *params,
>  
>      if (params->has_tls_creds) {
>          assert(params->tls_creds->type == QTYPE_QSTRING);
> +        if (dest->tls_creds) {
> +            g_free(dest->tls_creds);
> +        }
>          dest->tls_creds = g_strdup(params->tls_creds->u.s);
>      }
>  
>      if (params->has_tls_hostname) {
>          assert(params->tls_hostname->type == QTYPE_QSTRING);
> +        if (dest->tls_hostname) {
> +            g_free(dest->tls_hostname);
> +        }
>          dest->tls_hostname = g_strdup(params->tls_hostname->u.s);
>      }

Thanks for reporting the leak, but I don't think this is the right fix:

In the call chain we have, qmp_migrate_set_parameters calls:

    migrate_params_test_apply(params, &tmp);

tmp is a stack allocated variable  that becomes the 'dest'
we see here.  Then at the top of migrate_params_test_apply
we have:

    *dest = migrate_get_current()->parameters;

so that's probably bad; that's a shallow copy, so dest->tls_authz
points to the same storage as the real current migration parameters.

whne the code does:
    if (params->has_tls_creds) {
        assert(params->tls_creds->type == QTYPE_QSTRING);
        dest->tls_creds = g_strdup(params->tls_creds->u.s);
    }

it's only changing the pointer in the 'tmp' not the main copy
because of migrate_params_check fails then the parameters get entirely
unchanged.  So if you do a free on dest->tls_hostname you end up
freeing the real parameter that's still getting used, not the tmp.

So I think we need to:
  a) change migrate_params_test_apply so that it returns a
MigrationParameters *  rather than taking &tmp
  b) Make migrate_params_test use QAPI_CLONE to clone instead of doing:
         *dest = migrate_get_current()->parameters;
  c) Then do a qapi_free_MigrateParameters in qmp_migrate_set_parameters
    on both the true and false paths.

Does that make sense?

Dave


>  
> -- 
> 2.19.1
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK