Messages in this thread | | | Subject | Re: [PATCH AUTOSEL 4.19 08/38] media: pci: ttpci: av7110: fix possible buffer overflow caused by bad DMA value in debiirq() | From | Jia-Ju Bai <> | Date | Sun, 30 Aug 2020 15:24:24 +0800 |
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On 2020/8/29 20:10, Pavel Machek wrote: > Hi! > >> The value av7110->debi_virt is stored in DMA memory, and it is assigned >> to data, and thus data[0] can be modified at any time by malicious >> hardware. In this case, "if (data[0] < 2)" can be passed, but then >> data[0] can be changed into a large number, which may cause buffer >> overflow when the code "av7110->ci_slot[data[0]]" is used. >> >> To fix this possible bug, data[0] is assigned to a local variable, which >> replaces the use of data[0]. > I'm pretty sure hardware capable of manipulating memory can work > around any such checks, but... > >> +++ b/drivers/media/pci/ttpci/av7110.c >> @@ -424,14 +424,15 @@ static void debiirq(unsigned long cookie) >> case DATA_CI_GET: >> { >> u8 *data = av7110->debi_virt; >> + u8 data_0 = data[0]; >> >> - if ((data[0] < 2) && data[2] == 0xff) { >> + if (data_0 < 2 && data[2] == 0xff) { >> int flags = 0; >> if (data[5] > 0) >> flags |= CA_CI_MODULE_PRESENT; >> if (data[5] > 5) >> flags |= CA_CI_MODULE_READY; >> - av7110->ci_slot[data[0]].flags = flags; >> + av7110->ci_slot[data_0].flags = flags; > This does not even do what it says. Compiler is still free to access > data[0] multiple times. It needs READ_ONCE() to be effective. > >
Thanks for this advice, I will submit a v2 patch soon.
Best wishes, Jia-Ju Bai
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