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Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec")

Cross-posted to 2 groups.

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Tomas Janousek writes:
> On Fri, Oct 25, 2019 at 09:45:55AM +0200, Ansgar wrote:
>> Tomas Janousek suggested in https://bugs.debian.org/942881#41 that the
>> file might be truncated and two bytes missing.  I think that might be
>> the problem, but with three bytes missing:
>> 
>> src:linux-signed-amd64/5.3.7+1 has for linux-image-5.3.0-1-amd64 a total
>> of 3568 detached signatures: one is 1378 bytes (kernel itself), then
>> 3566 module signatures at 396 bytes each, then one module signature for
>> snd-hda-codec-hdmi.ko.sig which is only 393 bytes.  That is very
>> suspicious...
>
> Not really. That's just the ASN.1. For 256 byte octet string, the length field
> is one byte longer than for 255 or 254 bytes.

Ah, I see: the asn1parse output has hl=2 vs. hl=3.

> Yesterday I got one more idea: we've ruled out padding, but maybe a zero byte
> in the middle would somehow get lost. So I tried all the ways one could place
> two zero bytes into the 254 byte string, and got nothing.

I tried running `sign-file` manually and can reproduce the truncated
file with Debian's production key.  I also tried signing the same key
with a test key instead of the production key: then the signature is 256
bytes long, just as with any other file...

`strace -e write sign-file` reports only a single call to `write()`
which writes the entire file in one go.  The return value also matches
the number of bytes asked to be written in every case.

Ansgar

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Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Josh Triplett <josh@joshtriplett.org> - 2019-10-22 21:00 +0200
  Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Tomas Janousek <tomi@nomi.cz> - 2019-10-23 00:20 +0200
    Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Tomas Janousek <tomi@nomi.cz> - 2019-10-23 09:40 +0200
      Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Tomas Janousek <tomi@nomi.cz> - 2019-10-23 17:30 +0200
        Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Ben Hutchings <ben@decadent.org.uk> - 2019-10-25 04:00 +0200
          Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Ansgar <ansgar@43-1.org> - 2019-10-25 09:50 +0200
            Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Tomas Janousek <tomi@nomi.cz> - 2019-10-25 10:00 +0200
              Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Ansgar <ansgar@43-1.org> - 2019-10-25 11:10 +0200
                Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Tomas Janousek <tomi@nomi.cz> - 2019-10-25 11:30 +0200
                Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Ansgar <ansgar@43-1.org> - 2019-10-25 12:00 +0200
          Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Ansgar Burchardt <ansgar@debian.org> - 2019-10-25 10:30 +0200
            Bug#942881: Audio on Lenovo X1 Carbon 5th generation stopped working after upgrade to linux-image-5.3.0-1-amd64 ("No response from codec") Ben Hutchings <ben@decadent.org.uk> - 2019-10-25 15:20 +0200
  Bug#942881: Confirming bug on Dell XPS 13 9360R Wilhelm Westermark <wilhelm@westermark.org> - 2019-10-23 01:20 +0200

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