Channel name from an invite link's `b=` parameter is never reconciled with the channel's actual name

[bolstad]

• Operating System (Linux/Mac/Windows/iOS/Android): Mac
• Core Version: 2.49.0
• Client Version: Delta Chat Desktop 2.49.1

Expected behavior

When joining a broadcast channel through an invite link
(https://i.delta.chat/#...), the channel should be displayed with its
actual, current name: the same name the channel owner and every other
member sees.

Actual behavior

The device that opened the invite link permanently displays the name that
was embedded in the link's b= parameter.

If that value does not match the channel's current name (e.g. the channel was
renamed after the link was generated, or an older link was shared), the joining device
keeps the wrong name forever - even after it has received messages and membership
events from the channel.

This happens only on the device that opened the invite link. The
channel owner and all other clients display the correct name.

In the attached screenshot the channel is shown as "Knarkcentralen" both
in the chat list and the chat header. That string is exactly the b=
parameter of the invite link used to join the channel — not the channel's
real name:

https://i.delta.chat/#0D6A9C5D3E3DB037A352126C2EA02AFD2A77C33F&v=3&x=4KRXxEZVkaYMEmBqeID703kf&j=An4lktezRohvANysQdthJs3G&s=2Zjt9QxxSf68vl1uSqLfM1eg&a=p4r768hc7%40mailchat.pl&n=dekaminki&b=Knarkcentralen

The device has clearly received channel traffic afterwards. The info
messages "Du anslöt till kanalen." ("You joined the channel") / "Medlemmen … togs bort av dekaminski." ("Member was removed by dekaminski") are visible, yet the name was never corrected.

Steps to reproduce the problem

1. Device A: create a broadcast channel and name it Channel A.
2. Device A: generate an invite link (QR code → Show QR Invite Code → Share).
   The link now contains b=Channel%20A.
3. Device A: rename the channel to Channel B.
4. Device B: open the invite link from step 2 and join the channel.
5. Device A: post a message in the channel.
6. Device B shows the channel as Channel A, while Device A and all
   other members show Channel B.

The mismatch is also reproducible with any invite link whose b= value differs from the channel's current name.

This can be used in several ways for impersonation & phishing attacks.

Screenshots

[r10s]

before diving into the fix, i want to understand the issue.

i just tried, it was working as expected. i did the following:

1. create a new channel on desktop 2.49, name it foobar
2. take a screenshot of the join-qr-code (so that the old name is forced there)
3. rename the channel to foo renamed
4. scan the qr code screenshot with iOS 2.49
5. iOS asks correctly "Do you want to join the channel "foobar"?` (no network request is done before confirmation)
6. after network handshake, however, name is changed to foo renamed

i also tried the guide above with the sending of a message, was fine for me as well.

what shall i do differently to reproduce the issue?

[bolstad]

@r10s Sigh. I did several tests following the example, but the sync message was never received. But now, a couple of hours later channel rename name is nearly instantly propagated on the first device and can no longer reproduce it either 🤷.

[bolstad]

@r10s It appear that my example was bad and gave a false positive (due to som relay lag).

But here is an actual working example to reproduce:

• Let Alice create the Channel "Test A" and share the invite link.
• Let Bob take the invite link and replace the b= parameter to "Test+B" and join the chan

Expected behaviour:

• When Alice accept Bob to channel "Test A" and post updates, the channel name in Bobs client should be updated to "Test A"

Actual behavior:

• When Alice accept Bob to channel "Test A" and post updates, the channel name in Bobs client remain "Test B"

Live test case:

• Join this channel
• Wait for dekaminski to post
• Channel name remain "Knarkcentralen" on first device that is joined, but name on secondary device is correctly displayed as "Deltachat.se"