[pulseaudio-tickets] [Bug 102060] Security: PulseAudio server weakens the umask

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=102060

--- Comment #1 from Tanu Kaskinen <tanuk at iki.fi> ---
I don't understand why we set the umask at all.

If the old umask is so strict that it prevents pulseaudio from reading or
writing its own files, then that would seem to me just plain broken
configuration that we don't need to work around.

If the old umask is 0077, that could prevent clients from other users
communicating with the server, except that it doesn't. Connections from other
users are prevented anyway in the per-user mode (all created directories,
including the one where the socket is, have permissions 0700), and in the
system mode all directories are created with permissions 0755 regardless of the
umask. The socket file is always created with permissions 0777, so all users
always have access to the system mode socket.

If the old umask is overly lenient, then so what? Pulseaudio only creates files
in directories that it creates, and since in the per-user mode all directories
are created with permissions 0700, other users won't have access to those files
anyway.

Hmm, there's one case where there could be a problem: if pulseaudio runs in the
system mode, and it's started with umask 0000, then anyone can write to the
state files that pulseaudio creates. I think this could be solved by setting
the umask only in the system mode (the umask() call was actually added in the
commit that introduced the system mode, so the original purpose seems to be
system mode related anyway). While we're at it, the umask could be tightened to
0077, since the state files can reveal some slightly privacy-sensitive
information that shouldn't be readable by everyone.

Setting the umask to 0077 also in the per-user case probably wouldn't do any
harm, though. What possible use case is there for users to look at each others'
pulseaudio state files? Maybe we should just always set it to 0077.

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