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getenv.3: Document secure_getenv(3) 

Reviewed-by: Florian Weimer <fweimer@redhat.com>
Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2012-08-14 08:06:24 +02:00
parent e82600ef6e
commit 4e1927c6ec
1 changed files with 55 additions and 3 deletions
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58
man3/getenv.3
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@ -1,5 +1,5 @@
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright (C) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
.\" and Copyright (C) 2007, 2012 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
@ -28,15 +28,25 @@
.\" Modified Sat Jul 24 19:30:29 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aeb@cwi.nl)
.\"
.TH GETENV 3 2008-03-17 "GNU" "Linux Programmer's Manual"
.TH GETENV 3 2012-08-14 "GNU" "Linux Programmer's Manual"
.SH NAME
getenv \- get an environment variable
getenv, secure_getenv \- get an environment variable
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.sp
.BI "char *getenv(const char *" name );
.BI "char *secure_getenv(const char *" name );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR secure_setenv ():
_GNU_SOURCE
.SH DESCRIPTION
The
.BR getenv ()
@ -46,13 +56,47 @@ environment variable
and returns a pointer to the corresponding
.I value
string.
The GNU-specific
.BR secure_getenv ()
function is just like
.BR getenv ()
except that it returns NULL in cases where "secure execution" is required.
Secure execution is required if one of the following conditions
was true when the program run by the calling process was loaded:
.IP * 3
the process's effective user ID did not match its real user ID or
the process's effective group ID did not match its real group ID
(typically this is the result of executing a set-user-ID or
set-group-ID program);
.IP *
the effective capability bit was set on the executable file; or
.IP *
the process has a nonempty permitted capability set.
.PP
Secure execution may also required if triggered
by some Linux security modules.
The
.BR secure_getenv ()
function is intended for use in general-purpose libraries
to avoid vulnerabilities that could occur if
set-user-ID or set-group-ID programs accidentally
trusted the environment.
.SH "RETURN VALUE"
The
.BR getenv ()
function returns a pointer to the value in the
environment, or NULL if there is no match.
.SH "CONFORMING TO"
.BR getenv ():
SVr4, POSIX.1-2001, 4.3BSD, C89, C99.
.BR secure_getenv ()
is a GNU extension.
.SH VERSIONS
.BR secure_getenv ()
first appeared in glibc 2.17.
.SH NOTES
The strings in the environment list are of the form \fIname=value\fP.
@ -74,9 +118,17 @@ and can be modified by a subsequent call to
.BR setenv (3),
or
.BR unsetenv (3).
The "secure execution" mode of
.BR secure_getenv ()
is controlled by the
.B AT_SECURE
flag contained in the auxiliary vector passed from the kernel to user space.
.SH "SEE ALSO"
.BR clearenv (3),
.\" FIXME getauxval (3)
.BR putenv (3),
.BR setenv (3),
.BR unsetenv (3),
.BR capabilities (7),
.BR environ (7)