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.\" Copyright (c) 2003 Joseph Koshy <jkoshy@FreeBSD.org>
.\" Copyright (c) 2023 Olivier Certner <olce.freebsd@certner.fr>
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.Dd August 18, 2023
.Dt P_CANDEBUG 9
.Os
.Sh NAME
.Nm p_candebug
.Nd determine debuggability of a process
.Sh SYNOPSIS
.In sys/param.h
.In sys/proc.h
.Ft int
.Fn p_candebug "struct thread *td" "struct proc *p"
.Sh DESCRIPTION
This function determines if a given process
.Fa p
is debuggable by some thread
.Fa td .
.Pp
The following
.Xr sysctl 8
variables directly influence the behaviour of
.Fn p_candebug :
.Bl -tag -width indent
.It Va security.bsd.unprivileged_proc_debug
Must be set to a non-zero value to allow unprivileged processes
access to the kernel's debug facilities.
.It Va kern.securelevel
Debugging of the init process is not allowed if this variable is
.Li 1
or greater.
.El
.Pp
Other such variables indirectly influence it; see
.Xr cr_bsd_visible 9 .
.Sh RETURN VALUES
The
.Fn p_candebug
function
returns
.Li 0
if the process denoted by
.Fa p
is debuggable by thread
.Fa td ,
or a non-zero error return value otherwise.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EPERM
An unprivileged process attempted to debug another process but the system is
configured to deny it
.Po
see
.Xr sysctl 8
variable
.Va security.bsd.unprivileged_proc_debug
above
.Pc .
.It Bq Er ESRCH
Thread
.Fa td
has been jailed and the process to debug does not belong to the same jail or one
of its sub-jails, as determined by
.Xr prison_check 9 .
.It Bq Er ESRCH
.Xr cr_bsd_visible 9
denied visibility according to the BSD security policies in force.
.It Bq Er EPERM
Thread
.Fa td
lacks superuser credentials and its (effective) group set is not a superset of
process
.Fa p Ns 's
whole group set
.Pq "including real, effective and saved group IDs" .
.It Bq Er EPERM
Thread
.Fa td
lacks superuser credentials and its (effective) user ID does not match all user
IDs of process
.Fa p .
.It Bq Er EPERM
Thread
.Fa td
lacks superuser credentials and process
.Fa p
is executing a set-user-ID or set-group-ID executable.
.It Bq Er EPERM
Process
.Fa p
denotes the initial process
.Fn initproc
and the
.Xr sysctl 8
variable
.Va kern.securelevel
is greater than zero.
.It Bq Er EBUSY
Process
.Fa p
is in the process of being
.Fn exec Ns 'ed.
.It Bq Er EPERM
Process
.Fa p
denied debuggability
.Po
see
.Xr procctl 2 ,
command
.Dv PROC_TRACE_CTL
.Pc .
.El
.Sh SEE ALSO
.Xr prison_check 9 ,
.Xr mac 9 ,
.Xr cr_bsd_visible 9 ,
.Xr procctl 2 ,
.Xr p_cansee 9