Re: [PATCH] obexd: Fix crash of transfer pointer has being freed

[Luiz Augusto von Dentz <luiz.dentz@gmail.com>]

Hi Youwan,

On Wed, Jun 15, 2022 at 5:54 AM Youwan Wang <wangyouwan@uniontech.com> wrote:
>
> PC1 -> PC2 in the process of transferring the file,
> PC2 terminate the reception.
> It is found that PC1 will receive the Rcvd
> Forbiden message.
> transfer_response func is called and go to failed:
> transfer_complete func is called and go to transfer_free
>
> Invalid read of size 8
>     at 0x129C9B: put_get_data (gobex-transfer.c:138)
>     by 0x128675: get_body (gobex-packet.c:397)
>     by 0x128675: g_obex_packet_encode (gobex-packet.c:451)
>     by 0x1264ED: write_data (gobex.c:461)
>     by 0x1264ED: write_data (gobex.c:431)
>     by 0x49B7E97: g_main_context_dispatch ()
>     by 0x49B8287: ??? ()
>     by 0x49B8581: g_main_loop_run ()
>     by 0x120834: main (main.c:322)
>   Address 0x7300028 is 56 bytes inside a block of size 64 free'd
>     at 0x48369AB: free (vg_replace_malloc.c:530)
>     by 0x12A404: transfer_response (gobex-transfer.c:245)
>     by 0x126B02: handle_response (gobex.c:1128)
>     by 0x127087: incoming_data (gobex.c:1373)
>     by 0x49B7E97: g_main_context_dispatch ()
>     by 0x49B8287: ??? ()
>     by 0x49B8581: g_main_loop_run ()
>     by 0x120834: main (main.c:322)
>   Block was alloc'd at
>     at 0x4837B65: calloc (vg_replace_malloc.c:752)
>     by 0x49BD9D8: g_malloc0 ()
>     by 0x129A49: transfer_new (gobex-transfer.c:258)
>     by 0x12A612: g_obex_put_req_pkt (gobex-transfer.c:282)
>     by 0x12A612: g_obex_put_req_pkt (gobex-transfer.c:271)
>     by 0x145862: transfer_start_put (transfer.c:880)
>     by 0x145862: obc_transfer_start (transfer.c:911)
>     by 0x13B487: session_process_transfer (session.c:836)
>     by 0x13C128: session_process_queue (session.c:887)
>     by 0x13C128: session_process_queue (session.c:872)
>     by 0x13C18F: session_process (session.c:820)
>     by 0x49B7E97: g_main_context_dispatch (in /usr/lib/x86_64-linux-gnu/)
>     by 0x49B8287: ??? (in /usr/lib/x86_64-linux-gnu/)
>     by 0x49B8581: g_main_loop_run (in /usr/lib/x86_64-linux-gnu/)
>     by 0x120834: main (main.c:322)
> ---
>  gobex/gobex-transfer.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/gobex/gobex-transfer.c b/gobex/gobex-transfer.c
> index c94d018b2..8e97fc73e 100644
> --- a/gobex/gobex-transfer.c
> +++ b/gobex/gobex-transfer.c
> @@ -197,6 +197,14 @@ static void transfer_response(GObex *obex, GError *err, GObexPacket *rsp,
>         }
>
>         rspcode = g_obex_packet_get_operation(rsp, &final);
> +       if (rspcode == G_OBEX_RSP_FORBIDDEN) {
> +               err = g_error_new(G_OBEX_ERROR, rspcode, "%s",
> +                                               g_obex_strerror(rspcode));
> +               g_obex_debug(G_OBEX_DEBUG_ERROR, "%s", err->message);
> +               g_error_free(err);
> +               return;
> +       }

This is not quite right, in fact the if statement below already treat
such errors, we might be missing something like final:

/* Reset if final so it can no longer be cancelled */
if (final_rsp)
obex->pending_req = NULL;

This would be a problem on the remote implementation which is
indicating that perhaps it is just a temporary failure, anyway then:

id = transfer->req_id;
transfer->req_id = 0;

This resets the req_id so on transfer_free the following code is not run:

if (transfer->req_id > 0)
g_obex_cancel_req(transfer->obex, transfer->req_id, TRUE);

So either we have to restore the transfer->req_id = id or not reset it
to 0, so perhaps something like this works better:

diff --git a/gobex/gobex-transfer.c b/gobex/gobex-transfer.c
index c94d018b2..8fae65d8d 100644
--- a/gobex/gobex-transfer.c
+++ b/gobex/gobex-transfer.c
@@ -200,6 +200,11 @@ static void transfer_response(GObex *obex, GError
*err, GObexPacket *rsp,
        if (rspcode != G_OBEX_RSP_SUCCESS && rspcode != G_OBEX_RSP_CONTINUE) {
                err = g_error_new(G_OBEX_ERROR, rspcode, "%s",
                                                g_obex_strerror(rspcode));
+               /* If not marked as final response but transfer_complete gonna
+                * be called restore the req_id so it can be properly cancelled
+                */
+               if (!final)
+                       transport->req_id = id;
                goto failed;
        }

> +
>         if (rspcode != G_OBEX_RSP_SUCCESS && rspcode != G_OBEX_RSP_CONTINUE) {
>                 err = g_error_new(G_OBEX_ERROR, rspcode, "%s",
>                                                 g_obex_strerror(rspcode));
> --
> 2.20.1
>
>
>


-- 
Luiz Augusto von Dentz