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Subject: Re: coredumps disallowed when creds are changed?
To: Ravi Pokala <rpokala@freebsd.org>,
 "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>
References: <D0A57A0A-5416-44ED-B5C8-2FC5B45B6BCB@freebsd.org>
From: Eugene Grosbein <eugen@grosbein.net>
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Date: Tue, 9 Oct 2018 05:33:31 +0700
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09.10.2018 4:31, Ravi Pokala wrote:

> Greetings hackers.
> 
> core(5) states:
> 
>> By default, a process that changes user or group credentials
>> whether real or effective will not create a corefile.
>> This behaviour can be changed to generate a core dump by setting the sysctl(8) variable kern.sugid_coredump to 1.
> 
> Can someone explain why?

Real/effective user/group id often are changed for a process started
by non-privilegied user running set[ug]id binary like csh/chpass/passwd(1)
that can read sensitive system data similar to /etc/master.passwd
containing password hashes. If such utility reads sensitive data
and then crashes due to a bug, its coredump may leak data to unexpected places
of file system like /home partition, then go to a dump/backup of file system,
get uploaded offsite as part of backup etc. That should not happen by default.