Re: [PATCH] thunderbolt: Fix double free of drom buffer

[Andreas Noever]

On Mon, May 2, 2016 at 7:30 PM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> On Sun, Apr 10, 2016 at 12:48:27PM +0200, Andreas Noever wrote:
>> If tb_drom_read fails sw->drom is freed but not set to NULL. sw->drom
>> is then freed again in the error path of sw_switch_alloc.
>
> s/sw_switch_alloc/tb_switch_alloc/ ?
>
>> The bug can be triggered by unplugging a thunderbolt device shortly
>> after it is detected by the thunderbolt driver.
>>
>> Signed-off-by: Andreas Noever <andreas.noever@xxxxxxxxx>
>> Cc: Lukas Wunner <lukas@xxxxxxxxx>
>> Cc: stable@xxxxxxxxxxxxxxx
>
> How far back would this need to be applied?  What is the commit where
> the but was introduced?
>
> I applied this to pci/thunderbolt for v4.7 with the following
> changelog.  If I did it wrong, I'll gladly update it, especially if
> you have specific symptoms of a bug or oops that would help people
> find this fix.
>
>     thunderbolt: Fix double free of drom buffer
>
>     If tb_drom_read() fails, sw->drom is freed but not set to NULL.  sw->drom
>     is then freed again in the error path of tb_switch_alloc().
>
>     The bug can be triggered by unplugging a thunderbolt device shortly after
>     it is detected by the thunderbolt driver.
>
>     Clear sw->drom if tb_drom_read() fails.
The changelog is correct. The bug can be triggered starting from
343fcb8c ("thunderbolt: Fix nontrivial endpoint devices.") which is in
3.17-rc1. I observed crashes during subsequent hotplug operations (pci
core, sometimes in pciehp). But by nature of a double free bug these
were not very reliable (used kasan to track it down).

Thanks
Andreas


>     [bhelgaas: add Fixes:, stable versions of interest]
>     Fixes: 343fcb8c70d7 ("thunderbolt: Fix nontrivial endpoint devices.")
>     Signed-off-by: Andreas Noever <andreas.noever@xxxxxxxxx>
>     Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>     CC: stable@xxxxxxxxxxxxxxx  # v3.17+
>     CC: Lukas Wunner <lukas@xxxxxxxxx>
>
>> ---
>>  drivers/thunderbolt/eeprom.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/thunderbolt/eeprom.c b/drivers/thunderbolt/eeprom.c
>> index 0dde34e..545c60c 100644
>> --- a/drivers/thunderbolt/eeprom.c
>> +++ b/drivers/thunderbolt/eeprom.c
>> @@ -444,6 +444,7 @@ int tb_drom_read(struct tb_switch *sw)
>>       return tb_drom_parse_entries(sw);
>>  err:
>>       kfree(sw->drom);
>> +     sw->drom = NULL;
>>       return -EIO;
>>
>>  }
>> --
>> 2.8.0
>>
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