Messages in this thread | | | Date | Sat, 19 Jul 2008 12:32:35 +0200 | From | Stefan Richter <> | Subject | Re: PATCH] firewire: add padding to some struct |
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JiSheng Zhang wrote: > On Fri, 18 Jul 2008 17:27:44 +0200 > Mikael Pettersson <mikpe@it.uu.se> wrote: >> JiSheng Zhang writes: >> > --- old/drivers/firewire/fw-cdev.c 2008-07-14 05:51:29.000000000 +0800 >> > +++ new/drivers/firewire/fw-cdev.c 2008-07-18 20:20:45.841328585 +0800 >> > @@ -382,9 +382,9 @@ >> > >> > response->response.type = FW_CDEV_EVENT_RESPONSE; >> > response->response.rcode = rcode; >> > - queue_event(client, &response->event, >> > - &response->response, sizeof(response->response), >> > - response->response.data, response->response.length); >> > + queue_event(client, &response->event, &response->response, >> > + sizeof(response->response) + response->response.length, >> > + NULL, 0); >> > } >> >> Neither of these look correct. >> If sizeof(struct ...) != offsetof(struct ..., data) as you claim is possible, >> then the old code will copy too much to/from ->response but the correct amount >> to/from ->response.data, and the new code will copy too much to/from ->response.data. > > The old code will copy 4 extra bytes totally on some platforms, the new code > is correct. The old one queue like this: > struct ...(excluding the padding bytes)|4 padding bytes|4 padding bytes|data > >> That's why C has offsetof(): >> >> queue_event(client, &response->event, >> &response->response, >> offsetof(typeof(*response->responce), data), // I don't know the struct name >> response->response.data, response->response.length);
sizeof(struct ...) != offsetof(struct ..., data) happens for example on x86-64.
This is what I get with the current firewire drivers in a block read response from firecontrol on i686:
Command: r . 0 0xfffff0000400 20 reading from node 0, bus 1023, offset 0XFFFFF0000400 20 bytes read succeeded. Data follows (hex): 04 04 04 8F 31 33 39 34 F0 00 A2 22 00 10 DC 56 00 FE D2 D4 Ack code: complete
And the same on x86-64:
Command: r . 0 0xfffff0000400 20 reading from node 0, bus 1023, offset 0XFFFFF0000400 20 bytes read succeeded. Data follows (hex): 04 04 04 8F 04 04 04 8F 31 33 39 34 F0 00 A2 22 00 10 DC 56 Ack code: complete
Command: r . 0 0xfffff0000400 24 reading from node 0, bus 1023, offset 0XFFFFF0000400 20 bytes read succeeded. Data follows (hex): 04 04 04 8F 04 04 04 8F 31 33 39 34 F0 00 A2 22 00 10 DC 56 00 FE D2 D4 Ack code: complete
I used libraw1394 from Dan's git repo. Gscanbus shows exactly the same results. So, x86-64 and all other architectures where struct fw_cdev_event* are aligned on u64 boundaries are currently seriously broken... but nobody noticed it before. The only breakage which I saw (and is obviously the result of this bug) is that gscanbus shows a wrong bus topology on x86-64 but the correct one on i686. The damage from this bug is limited though because - most applications send requests which get responses with 0 or 4 bytes payload, - no application (which can run on both old and new stack without change) uses address range mappings, i.e. get incoming requests.
I'll look further into your proposed fix. -- Stefan Richter -=====-==--- -=== =--== http://arcgraph.de/sr/
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