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SubjectRe: KMSAN: uninit-value in alauda_check_media
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Le 28/12/2021 à 23:49, Alan Stern a écrit :
> On Tue, Dec 28, 2021 at 08:47:15AM +0100, Christophe JAILLET wrote:
>> Hi,
>>
>> (2nd try - text only format - sorry for the noise)
>>
>>
>> first try to use syzbot. I hope I do it right.
>> Discussion about the syz report can be found at
>> https://lore.kernel.org/linux-kernel/0000000000007d25ff059457342d@google.com/
>>
>> This patch only test if alauda_get_media_status() (and its embedded
>> usb_stor_ctrl_transfer()) before using the data.
>> In case of error, it returns USB_STOR_TRANSPORT_ERROR as done elsewhere.
>>
>> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
>> master
>>
>> CJ
>>
>
>> diff --git a/drivers/usb/storage/alauda.c b/drivers/usb/storage/alauda.c
>> index 20b857e97e60..6c486d964911 100644
>> --- a/drivers/usb/storage/alauda.c
>> +++ b/drivers/usb/storage/alauda.c
>> @@ -318,7 +318,8 @@ static int alauda_get_media_status(struct us_data *us, unsigned char *data)
>> rc = usb_stor_ctrl_transfer(us, us->recv_ctrl_pipe,
>> command, 0xc0, 0, 1, data, 2);
>>
>> - usb_stor_dbg(us, "Media status %02X %02X\n", data[0], data[1]);
>> + if (rc == USB_STOR_XFER_GOOD)
>> + usb_stor_dbg(us, "Media status %02X %02X\n", data[0], data[1]);
>
> Instead of adding this test, you could initialize data[0] and data[1]
> to zero before the call to usb_stor_ctrl_transfer.

Well, having the test is cleaner, IMHO.
If usb_stor_ctrl_transfer() fails, a message explaining the reason is
already generated by the same usb_stor_dbg(). Having an error message
followed by another one stating that the Media Status is 0x00 0x00 could
be confusing I think.

Let me know if you have a real preference for a memset(data, 0, 2).
If so, I'll add it.

>
>>
>> return rc;
>> }
>> @@ -453,8 +454,11 @@ static int alauda_check_media(struct us_data *us)
>> {
>> struct alauda_info *info = (struct alauda_info *) us->extra;
>> unsigned char status[2];
>> + int rc;
>>
>> - alauda_get_media_status(us, status);
>> + rc = alauda_get_media_status(us, status);
>> + if (rc != USB_STOR_TRANSPORT_GOOD)
>> + return USB_STOR_TRANSPORT_ERROR;
>>
>> /* Check for no media or door open */
>> if ((status[0] & 0x80) || ((status[0] & 0x1F) == 0x10)
>
> In general this looks fine. Let us know when you are ready to submit
> the patch.

I was unsure that this patch would get any interest because the driver
looks old. That's why I first tried to play with syzbot :)

In the syzbot history, you also mentioned that 'unsigned char status[2]'
should be 'unsigned char *status = us->iobuf;'

This is more a blind fix for me, but it looks consistent with other
places that call alauda_get_media_status().

So, once you confirm if you prefer my 'if' or a 'memset', I'll resend a
small serie for fixing both issues.

CJ


>
> Alan Stern
>

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