vga_init(3) Svgalib User Manual vga_init(3)NAMEvga_init - initialize svgalib library
SYNOPSIS
#include <vga.h>
int vga_init(void);
DESCRIPTION
It detects the chipset and gives up supervisor rights. This is the rec‐
ommended first line of any program that uses svgalib.
vga_setchipset(3) can be called before it to avoid detection.
Svgalib catches a bunch of signals that usually kill your program to
restore textmode. If you catch signal's before calling vga_init()
svgalib will restore textmode and prepare for shutdown and then call
your handler routine. If you don't want this, catch the signal after
calling vga_init and do not daisychain to svgalib's original handler.
WARNING! svgalib needs two signals for it's own purposes (that is man‐
aging console switches). To avoid problems it uses the otherwise unused
signals SIGUSR1 and SIGUSR2. However, this means that you cannot use
them in your program by any means. They are setup by vga_init() as
everything else is.
Since version 1.2.11 vga_init() includes code to hunt for a free vir‐
tual console on its own in case you are not starting the program from
one (but instead over a network or modem login, from within 'screen' or
an 'xterm'). Provided there is a free console, this succeeds if you are
root or if the svgalib calling user own the current console. This is to
avoid people not using the console being able to fiddle with it. On
graceful exit the program returns to the console from which it was
started. Otherwise it remains in text mode at the VC which svgalib
allocated to allow you to see any error messages. In any case, any I/O
the svgalib makes in text mode (after calling vga_init) will also take
place at this new console.
Alas, some games misuse their suid root privilege and run as full root
process. svgalib cannot detect this and allows Joe Blow User to open a
new VC on the console. If this annoys you ROOT_VC_SHORTCUT in Make‐
file.cfg allows you to disable allocating a new VC for root (except
when he owns the current console) when compiling svgalib. This is the
default (disabling the allocation for root).
vga_init() returns a non-zero value in case of errors. As of this writ‐
ing it will return -1 if it is unable to allocate a graphical console.
Otherwise, 0 is returned.
BUGS
Svgalib versions prior to 1.2.11 had a security hole where it would be
possible to regain root privileges even after a vga_init() call. This
is not necessarily a problem, but if your program is vulnerable to buf‐
fer overflows and other attacks, an attacker may exploit this.
However, prior to your call, your program will need to run setuid root,
so you should be very careful. The ioperm library by Olaf Titz will
allow svgalib programs to run not setuid root. However, it gives all
programs unlimited access to the hardware. Again, a malicious person
can exploit this (albeit a bit more difficult) too. Thus, in general,
make your svgalib programs as secure as any setuid root program.
Some programs may (accidently) rely on the old behaviour (which was
probably due to the author not knowing about saved uids (which might
actually even not have existed in Linux at that time)). A line:
security compat
in the configuration file /etc/vga/libvga.conf will reinstate the old
behaviour whereas
security revoke-all-privs
enables the (currently default) action.
SEE ALSOsvgalib(7), vga_setmode(3), mouse_init(3), vga_claimvideomemory(3),
vga_ext_set(3), vga_fillblt(3), vga_getcurrentchipset(3), vga_getde‐
faultmode(3), vga_getgraphmem(3), vga_runinbackground(3), vga_runin‐
background_version(3), vga_safety_fork(3), vga_setchipset(3),
vga_setchipsetandfeatures(3), vgagl(7), libvga.config(5),
AUTHOR
This manual page was edited by Michael Weller <eowmob@exp-math.uni-
essen.de>. The exact source of the referenced function as well as of
the original documentation is unknown.
It is very likely that both are at least to some extent are due to Harm
Hanemaayer <H.Hanemaayer@inter.nl.net>.
Occasionally this might be wrong. I hereby asked to be excused by the
original author and will happily accept any additions or corrections to
this first version of the svgalib manual.
Svgalib (>= 1.2.11) 27 July 1997 vga_init(3)
