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Add COMMAND EXECUTION section that describes how sudo runs

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the command, the extra sudo processes and signal handling.
This commit is contained in:
Todd C. Miller
2012-08-21 13:01:43 -04:00
parent c1d6e86d67
commit 8f3232ee69
6 changed files with 373 additions and 16 deletions
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4
doc/Makefile.in
View File

@@ -111,13 +111,13 @@ $(srcdir)/sudo.man.in: $(srcdir)/sudo.mdoc.in
fi
sudo.man.sed: $(srcdir)/fixman.sh
BAMAN=@BAMAN@ LCMAN=@LCMAN@ SEMAN=@SEMAN@ $(SHELL) $(srcdir)/fixman.sh $@
BAMAN=@BAMAN@ LCMAN=@LCMAN@ SEMAN=@SEMAN@ PSMAN=@PSMAN@ $(SHELL) $(srcdir)/fixman.sh $@
sudo.man: $(srcdir)/sudo.man.in sudo.man.sed
(cd $(top_builddir) && $(SHELL) config.status --file=-) < $(srcdir)/$@.in | $(SED) -f $@.sed > $@
sudo.mdoc.sed: $(srcdir)/fixmdoc.sh
BAMAN=@BAMAN@ LCMAN=@LCMAN@ SEMAN=@SEMAN@ $(SHELL) $(srcdir)/fixmdoc.sh $@
BAMAN=@BAMAN@ LCMAN=@LCMAN@ SEMAN=@SEMAN@ PSMAN=@PSMAN@ $(SHELL) $(srcdir)/fixmdoc.sh $@
sudo.mdoc: $(srcdir)/sudo.mdoc.in sudo.mdoc.sed
(cd $(top_builddir) && $(SHELL) config.status --file=-) < $(srcdir)/$@.in | $(SED) -f $@.sed > $@

25
doc/fixman.sh
View File

@@ -42,6 +42,12 @@ case "$OUTFILE" in
/^\\fB\\-c\\fR \\fIclass\\fR$/,/^\.TP 12n$/ {
/^\.PD$/!d
}
/^login_cap(3),$/d
/^BSD login class$/ {
N
N
/^BSD login class\n\.TP 4n\n\\fBo\\fR$/d
}
EOF
fi
@@ -52,6 +58,25 @@ case "$OUTFILE" in
/^\\fB\\-[rt]\\fR \\fI[rt][oy][lp]e\\fR$/,/^\.TP 12n$/ {
/^\.PD$/!d
}
/^SELinux role and type$/ {
N
N
/^SELinux role and type\n\.TP 4n\n\\fBo\\fR$/d
}
EOF
fi
# Solaris privileges
if [ X"$PSMAN" != X"1" ]; then
cat >>"$OUTFILE" <<-'EOF'
/^Solaris project$/ {
N
N
N
N
N
/^Solaris project\n\.TP 4n\n\\fBo\\fR\nSolaris privileges\n\.TP 4n\n\\fBo\\fR$/d
}
EOF
fi
;;

20
doc/fixmdoc.sh
View File

@@ -35,6 +35,10 @@ case "$OUTFILE" in
d
}
/^\.Xr login_cap 3 ,$/d
/^BSD login class$/ {
N
/^BSD login class\n\.It$/d
}
EOF
fi
@@ -49,6 +53,22 @@ case "$OUTFILE" in
/^\.It Fl t Ar type/,/specified role\.$/ {
d
}
/^SELinux role and type$/ {
N
/^SELinux role and type\n\.It$/d
}
EOF
fi
# Solaris privileges
if [ X"$PSMAN" != X"1" ]; then
cat >>"$OUTFILE" <<-'EOF'
/^Solaris project$/ {
N
N
N
/^Solaris project\n\.It\nSolaris privileges\n\.It$/d
}
EOF
fi

73
doc/sudo.cat
View File

@@ -18,10 +18,7 @@ SSYYNNOOPPSSIISS
DDEESSCCRRIIPPTTIIOONN
ssuuddoo allows a permitted user to execute a _c_o_m_m_a_n_d as the superuser or
another user, as specified by the security policy. The real and
effective uid and gid are set to match those of the target user, as
specified in the password database, and the group vector is initialized
based on the group database (unless the --PP option was specified).
another user, as specified by the security policy.
ssuuddoo supports a plugin architecture for security policies and
input/output logging. Third parties can develop and distribute their own
@@ -300,6 +297,74 @@ DDEESSCCRRIIPPTTIIOONN
the user may set variables that would otherwise be forbidden. See
sudoers(4) for more information.
CCOOMMMMAANNDD EEXXEECCUUTTIIOONN
When ssuuddoo executes a command, the security policy specifies the execution
envionment for the command. Typically, the real and effective uid and
gid are set to match those of the target user, as specified in the
password database, and the group vector is initialized based on the group
database (unless the --PP option was specified).
The following parameters may be specified by security policy:
oo real and effective user ID
oo real and effective group ID
oo supplementary group IDs
oo the environment list
oo current working directory
oo file creation mode mask (umask)
oo SELinux role and type
oo Solaris project
oo Solaris privileges
oo BSD login class
oo scheduling priority (aka nice value)
PPrroocceessss MMooddeell
When ssuuddoo runs a command, it calls fork(2), sets up the execution
environment as described above, and calls the execve system call in the
child process. The main ssuuddoo process waits until the command has
completed, then passes the command's exit status to the security policy's
close method and exits. If an I/O logging plugin is configured, a new
pseudo-terminal (``pty'') is created and a second ssuuddoo process is used to
relay job control signals between the user's existing pty and the new pty
the command is being run in. This extra process makes it possible to,
for example, suspend and resume the command. Without it, the command
would be in what POSIX terms an ``orphaned process group'' and it would
not receive any job control signals.
SSiiggnnaall HHaannddlliinngg
Because the command is run as a child of the ssuuddoo process, ssuuddoo will
relay signals it receives to the command. Unless the command is being
run in a new pty, the SIGHUP, SIGINT and SIGQUIT signals are not relayed
unless they are sent by a user process, not the kernel. Otherwise, the
command would receive SIGINT twice every time the user entered control-C.
Some signals, such as SIGSTOP and SIGKILL, cannot be caught and thus will
not be relayed to the command. As a general rule, SIGTSTP should be used
instead of SIGSTOP when you wish to suspend a command being run by ssuuddoo.
As a special case, ssuuddoo will not relay signals that were sent by the
command it is running. This prevents the command from accidentally
killing itself. On some systems, the reboot(1m) command sends SIGTERM to
all non-system processes other than itself before rebooting the systyem.
This prevents ssuuddoo from relaying the SIGTERM signal it received back to
reboot(1m), which might then exit before the system was actually rebooted,
leaving it in a half-dead state similar to single user mode. Note,
however, that this check only applies to the command run by ssuuddoo and not
any other processes that the command may create. As a result, running a
script that calls reboot(1m) or shutdown(1m) via ssuuddoo may cause the system
to end up in this undefined state unless the reboot(1m) or shutdown(1m) are
run using the eexxeecc() family of functions instead of ssyysstteemm() (which
interposes a shell between the command and the calling process).
PPLLUUGGIINNSS
Plugins are dynamically loaded based on the contents of the
_/_e_t_c_/_s_u_d_o_._c_o_n_f file. If no _/_e_t_c_/_s_u_d_o_._c_o_n_f file is present, or it

138
doc/sudo.man.in
View File

@@ -85,11 +85,6 @@ allows a permitted user to execute a
\fIcommand\fR
as the superuser or another user, as specified by the security
policy.
The real and effective uid and gid are set to match those of the
target user, as specified in the password database, and the group
vector is initialized based on the group database (unless the
\fB\-P\fR
option was specified).
.PP
\fBsudo\fR
supports a plugin architecture for security policies and input/output
@@ -695,6 +690,139 @@ the user may set variables that would otherwise be forbidden.
See
sudoers(@mansectform@)
for more information.
.SH "COMMAND EXECUTION"
When
\fBsudo\fR
executes a command, the security policy specifies the execution
envionment for the command.
Typically, the real and effective uid and gid are set to
match those of the target user, as specified in the password database,
and the group vector is initialized based on the group database
(unless the
\fB\-P\fR
option was specified).
.PP
The following parameters may be specified by security policy:
.TP 4n
\fBo\fR
real and effective user ID
.TP 4n
\fBo\fR
real and effective group ID
.TP 4n
\fBo\fR
supplementary group IDs
.TP 4n
\fBo\fR
the environment list
.TP 4n
\fBo\fR
current working directory
.TP 4n
\fBo\fR
file creation mode mask (umask)
.TP 4n
\fBo\fR
SELinux role and type
.TP 4n
\fBo\fR
Solaris project
.TP 4n
\fBo\fR
Solaris privileges
.TP 4n
\fBo\fR
BSD login class
.TP 4n
\fBo\fR
scheduling priority (aka nice value)
.SS "Process Model"
When
\fBsudo\fR
runs a command, it calls
fork(2),
sets up the execution environment as described above, and calls the
execve
system call in the child process.
The main
\fBsudo\fR
process waits until the command has completed, then passes the
command's exit status to the security policy's close method and exits.
If an I/O logging plugin is configured, a new pseudo-terminal
(``pty'')
is created and a second
\fBsudo\fR
process is used to relay job control signals between the user's
existing pty and the new pty the command is being run in.
This extra process makes it possible to, for example, suspend
and resume the command.
Without it, the command would be in what POSIX terms an
``orphaned process group''
and it would not receive any job control signals.
.SS "Signal Handling"
Because the command is run as a child of the
\fBsudo\fR
process,
\fBsudo\fR
will relay signals it receives to the command.
Unless the command is being run in a new pty, the
\fRSIGHUP\fR,
\fRSIGINT\fR
and
\fRSIGQUIT\fR
signals are not relayed unless they are sent by a user process,
not the kernel.
Otherwise, the command would receive
\fRSIGINT\fR
twice every time the user entered control-C.
Some signals, such as
\fRSIGSTOP\fR
and
\fRSIGKILL\fR,
cannot be caught and thus will not be relayed to the command.
As a general rule,
\fRSIGTSTP\fR
should be used instead of
\fRSIGSTOP\fR
when you wish to suspend a command being run by
\fBsudo\fR.
.PP
As a special case,
\fBsudo\fR
will not relay signals that were sent by the command it is running.
This prevents the command from accidentally killing itself.
On some systems, the
reboot(@mansectsu@)
command sends
\fRSIGTERM\fR
to all non-system processes other than itself before rebooting
the systyem.
This prevents
\fBsudo\fR
from relaying the
\fRSIGTERM\fR
signal it received back to
reboot(@mansectsu@),
which might then exit before the system was actually rebooted,
leaving it in a half-dead state similar to single user mode.
Note, however, that this check only applies to the command run by
\fBsudo\fR
and not any other processes that the command may create.
As a result, running a script that calls
reboot(@mansectsu@)
or
shutdown(@mansectsu@)
via
\fBsudo\fR
may cause the system to end up in this undefined state unless the
reboot(@mansectsu@)
or
shutdown(@mansectsu@)
are run using the
\fBexec\fR()
family of functions instead of
\fBsystem\fR()
(which interposes a shell between the command and the calling process).
.SH "PLUGINS"
Plugins are dynamically loaded based on the contents of the
\fI@sysconfdir@/sudo.conf\fR

129
doc/sudo.mdoc.in
View File

@@ -125,11 +125,6 @@ allows a permitted user to execute a
.Ar command
as the superuser or another user, as specified by the security
policy.
The real and effective uid and gid are set to match those of the
target user, as specified in the password database, and the group
vector is initialized based on the group database (unless the
.Fl P
option was specified).
.Pp
.Nm sudo
supports a plugin architecture for security policies and input/output
@@ -688,6 +683,130 @@ the user may set variables that would otherwise be forbidden.
See
.Xr sudoers @mansectform@
for more information.
.Sh COMMAND EXECUTION
When
.Nm sudo
executes a command, the security policy specifies the execution
envionment for the command.
Typically, the real and effective uid and gid are set to
match those of the target user, as specified in the password database,
and the group vector is initialized based on the group database
(unless the
.Fl P
option was specified).
.Pp
The following parameters may be specified by security policy:
.Bl -bullet
.It
real and effective user ID
.It
real and effective group ID
.It
supplementary group IDs
.It
the environment list
.It
current working directory
.It
file creation mode mask (umask)
.It
SELinux role and type
.It
Solaris project
.It
Solaris privileges
.It
BSD login class
.It
scheduling priority (aka nice value)
.El
.Ss Process Model
When
.Nm sudo
runs a command, it calls
.Xr fork 2 ,
sets up the execution environment as described above, and calls the
.Xr execve
system call in the child process.
The main
.Nm sudo
process waits until the command has completed, then passes the
command's exit status to the security policy's close method and exits.
If an I/O logging plugin is configured, a new pseudo-terminal
.Pq Dq pty
is created and a second
.Nm sudo
process is used to relay job control signals between the user's
existing pty and the new pty the command is being run in.
This extra process makes it possible to, for example, suspend
and resume the command.
Without it, the command would be in what POSIX terms an
.Dq orphaned process group
and it would not receive any job control signals.
.Ss Signal Handling
Because the command is run as a child of the
.Nm sudo
process,
.Nm sudo
will relay signals it receives to the command.
Unless the command is being run in a new pty, the
.Dv SIGHUP ,
.Dv SIGINT
and
.Dv SIGQUIT
signals are not relayed unless they are sent by a user process,
not the kernel.
Otherwise, the command would receive
.Dv SIGINT
twice every time the user entered control-C.
Some signals, such as
.Dv SIGSTOP
and
.Dv SIGKILL ,
cannot be caught and thus will not be relayed to the command.
As a general rule,
.Dv SIGTSTP
should be used instead of
.Dv SIGSTOP
when you wish to suspend a command being run by
.Nm sudo .
.Pp
As a special case,
.Nm sudo
will not relay signals that were sent by the command it is running.
This prevents the command from accidentally killing itself.
On some systems, the
.Xr reboot @mansectsu@
command sends
.Dv SIGTERM
to all non-system processes other than itself before rebooting
the systyem.
This prevents
.Nm sudo
from relaying the
.Dv SIGTERM
signal it received back to
.Xr reboot @mansectsu@ ,
which might then exit before the system was actually rebooted,
leaving it in a half-dead state similar to single user mode.
Note, however, that this check only applies to the command run by
.Nm sudo
and not any other processes that the command may create.
As a result, running a script that calls
.Xr reboot @mansectsu@
or
.Xr shutdown @mansectsu@
via
.Nm sudo
may cause the system to end up in this undefined state unless the
.Xr reboot @mansectsu@
or
.Xr shutdown @mansectsu@
are run using the
.Fn exec
family of functions instead of
.Fn system
(which interposes a shell between the command and the calling process).
.Sh PLUGINS
Plugins are dynamically loaded based on the contents of the
.Pa @sysconfdir@/sudo.conf