talloc_abort in notmuch_thread_get_tags () when db has been modified

[David Bremner]

Gaute Hope <eg at gaute.vetsj.com> writes:

> Hi,
>
> a user of astroid [0] ran into a issue [1] (full trace at issue) where
> reading a long query causes a talloc_abort in notmuch_thread_get_tags
> (). 'notmuch new' is running at the same time, and most likely a thread
> in the query has been modified since the query was done. Note that a
> notmuch_thread_get_authors () call returns NULL without causing a full
> crash. The code causing the crash is:
>
> ```
>     for (tags = notmuch_thread_get_tags (nm_thread);
>          notmuch_tags_valid (tags);
>          notmuch_tags_move_to_next (tags))
>     {
>       tag = notmuch_tags_get (tags); // tag belongs to tags
>     }
>
>     // or db.cc:508 in astroid/src.
> ```
>

The most likely cause of such a crash looks to me like nm_thread is NULL
or corrupted when passed in to get_tags. It's used without checking as a
talloc context, and that call to talloc never returns.