logind: Fix user_elect_display() to be more stable #56
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Patch looks mostly good. Please fix the issues I mentioned and it should be good to go. |
The previous implementation of user_elect_display() could easily end up overwriting the user’s valid graphical session with a new TTY session. For example, consider the situation where there is one session: c1, type = SESSION_X11, !stopping, class = SESSION_USER it is initially elected as the user’s display (i.e. u->display = c1). If another session is started, on a different VT, the sessions_by_user list becomes: c1, type = SESSION_X11, !stopping, class = SESSION_USER c2, type = SESSION_TTY, !stopping, class = SESSION_USER In the previous code, graphical = c1 and text = c2, as expected. However, neither graphical nor text fulfil the conditions for setting u->display = graphical (because neither is better than u->display), so the code falls through to check the text variable. The conditions for this match, as u->display->type != SESSION_TTY (it’s actually SESSION_X11). Hence u->display is set to c2, which is incorrect, because session c1 is still valid. Refactor user_elect_display() to use a more explicit filter and pre-order comparison over the sessions. This can be demonstrated to be stable and only ever ‘upgrade’ the session to a more graphical one. https://bugs.freedesktop.org/show_bug.cgi?id=90769
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LGTM. |
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Applied, thanks. |
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Guys, the line breaks are all fucked up on this one, please read up on CODING_STYLE on this! |
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Fixed the coding style issues now in cde40ac |
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The previous implementation of user_elect_display() could easily end up
overwriting the user’s valid graphical session with a new TTY session.
For example, consider the situation where there is one session:
c1, type = SESSION_X11, !stopping, class = SESSION_USER
it is initially elected as the user’s display (i.e. u->display = c1).
If another session is started, on a different VT, the sessions_by_user
list becomes:
c1, type = SESSION_X11, !stopping, class = SESSION_USER
c2, type = SESSION_TTY, !stopping, class = SESSION_USER
In the previous code, graphical = c1 and text = c2, as expected.
However, neither graphical nor text fulfil the conditions for setting
u->display = graphical (because neither is better than u->display), so
the code falls through to check the text variable. The conditions for
this match, as u->display->type != SESSION_TTY (it’s actually
SESSION_X11). Hence u->display is set to c2, which is incorrect, because
session c1 is still valid.
Refactor user_elect_display() to use a more explicit filter and
pre-order comparison over the sessions. This can be demonstrated to be
stable and only ever ‘upgrade’ the session to a more graphical one.
https://bugs.freedesktop.org/show_bug.cgi?id=90769