Messages in this thread | | | Date | Fri, 23 Jan 2015 15:16:23 +0100 | From | Jonas Danielsson <> | Subject | Regression introduced by commit dbe9a4173ea53 |
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Hi,
I have seen a regression, that I think is caused by:
commit dbe9a4173ea53b72b2c35d19f676a85b69f1c9fe Author: Eric W. Biederman <ebiederm@xmission.com> Date: Thu Sep 6 18:20:01 2012 +0000
scm: Don't use struct ucred in NETLINK_CB and struct scm_cookie.
With this commit the value send as uid when credentials are missing changes from -1 to overflowuid (default -2, the 'nobody' user).
I was using dbus-send to perform a method call on a gdbus server. And sometimes I fall victim to the race condition caused by:
commit 16e5726 ("af_unix: dont send SCM_CREDENTIALS by default")
And then there will be no credentials on the socket. The glib library checks the uid, and if it is -1, it will fall back to using SO_PEERCRED and things will work for me. But since the commit in $subject changes the uid I get failure with NoReply from dbus-send.
It seems that before the commit in $subject that the function from_kuid_munged was only called if there were credentials present. Otherwise we would set uid to -1. Now uid gets set to -1 if there is no credentials but from_kuid_munged is always called. And from the documentation of from_kuid_munged it states that it 'never fails and always returns a valid uid'. And in the case of uid being -1, it returns overflowuid.
So this seems like it broke glib. Caused by 1) the introduced race condition that makes it not totally safe to set SO_PEERCRED on the accepted socket and 2) that the value of uid when credentials are missing changed from -1 to overflowuid.
Thanks for your time Jonas
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