segmentation fault when decoding with webcam

[Niko Zurstraßen]

Hi all,

When trying to decode wifi codes with my webcam, qtqr crashes with the following output:

Traceback (most recent call last):
  File "/usr/bin/qtqr", line 723, in decodeWebcam
    if qr.data_decode[qr.data_type](qr.data) == 'NULL':
  File "/usr/lib/python2.7/dist-packages/qrtools.py", line 92, in <lambda>
    'wifi' : lambda data: re.findall(u"WIFI:S:(.*);T:(.*);P:(.*);;", data, re.IGNORECASE)[0],
IndexError: list index

After a little investigation I found out that my smartphone generates the qr codes, which I try to scan, incorrectly. Instead of two semicolons the MeCard like format ends with only one semicolon.
Thus, the regex-expression yields no result and the indexing with [0] fails.

As a fix I would suggest to put "qr.data_decode[qr.data_type](qr.data)" into a try/except block
and show an error box including the undecodable string if there was an IndexError.

Any ideas/comments on that?

[Ramiro Algozino (algozino)]

Hi!

Thanks for the report. I agree that the regex is failing and then making the app crash. I think that the right way would be to wrap all the decoders in a try-catch and just fallback to show the decoded text. I wouldn’t touch the regex because the QR code is malformed.

Feel free to send a PR!

Ramiro Algozino
https://algozino.com.ar/
On 25 Dec 2020, 10:25 +0100, Niko Zurstraßen <email address hidden>, wrote:
> Public bug reported:
>
> Hi all,
>
> When trying to decode wifi codes with my webcam, qtqr crashes with the
> following output:
>
> Traceback (most recent call last):
> File "/usr/bin/qtqr", line 723, in decodeWebcam
> if qr.data_decode[qr.data_type](qr.data) == 'NULL':
> File "/usr/lib/python2.7/dist-packages/qrtools.py", line 92, in <lambda>
> 'wifi' : lambda data: re.findall(u"WIFI:S:(.*);T:(.*);P:(.*);;", data, re.IGNORECASE)[0],
> IndexError: list index
>
>
> After a little investigation I found out that my smartphone generates the qr codes, which I try to scan, incorrectly. Instead of two semicolons the MeCard like format ends with only one semicolon.
> Thus, the regex-expression yields no result and the indexing with [0] fails.
>
> As a fix I would suggest to put "qr.data_decode[qr.data_type](qr.data)" into a try/except block
> and show an error box including the undecodable string if there was an IndexError.
>
> Any ideas/comments on that?
>
> ** Affects: qr-tools
> Importance: Undecided
> Status: New
>
> --
> You received this bug notification because you are a member of QR Tools
> Team, which is subscribed to QR Tools.
> https://bugs.launchpad.net/bugs/1909309
>
> Title:
> segmentation fault when decoding with webcam
>
> Status in QR Tools:
> New
>
> Bug description:
> Hi all,
>
> When trying to decode wifi codes with my webcam, qtqr crashes with the
> following output:
>
> Traceback (most recent call last):
> File "/usr/bin/qtqr", line 723, in decodeWebcam
> if qr.data_decode[qr.data_type](qr.data) == 'NULL':
> File "/usr/lib/python2.7/dist-packages/qrtools.py", line 92, in <lambda>
> 'wifi' : lambda data: re.findall(u"WIFI:S:(.*);T:(.*);P:(.*);;", data, re.IGNORECASE)[0],
> IndexError: list index
>
>
> After a little investigation I found out that my smartphone generates the qr codes, which I try to scan, incorrectly. Instead of two semicolons the MeCard like format ends with only one semicolon.
> Thus, the regex-expression yields no result and the indexing with [0] fails.
>
> As a fix I would suggest to put "qr.data_decode[qr.data_type](qr.data)" into a try/except block
> and show an error box including the undecodable string if there was an IndexError.
>
> Any ideas/comments on that?
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/qr-tools/+bug/1909309/+subscriptions

[Niko Zurstraßen (chciken)]

I sent a PR.
Please tell me if can improve something.

[Ramiro Algozino (algozino)]

Hi Niko,

Thank you for taking care of this. I've merged your PR, the fix should be available soon on the Daily PPA (tonight - tomorrow at max).

Best regards and have a happy new year!

[X-Ander (x-ander)]

Hi! I have found out that some smartphones generate wifi QR-codes having different order of attributes. Something like:

   WIFI:T:WPA;P:<key>;S:<ssid>;

So the program crashes. I have replaced the regular expression in qrtools.py by:

   WIFI:(?:;|S:([^;]*);|T:([^;]*);|P:([^;]*);|H:([^;]*);)+

Now it works. Attributes may be in random order, and may be missing as well.

[Ramiro Algozino (algozino)]

Thanks X-Ander, that makes sense actually!

I've pushed the regex you provided, should be available in the daily PPA soon.

Cheers!