.TH UNSAFE 2
.SH NAME
unsafe \- detect potential file security violations
.SH SYNOPSIS
.B #include <sys/types.h>
.PP
.B unsafe(nfd, readfds, writefds)
.br
.B fd_set *readfds, *writefds;
.SH DESCRIPTION
.I Unsafe
examines file descriptors 0 through
.I nfd\-1
and sets the corresponding bits of the masks in
.I readfds
and
.I writefds
to indicate files that are not known to be safe (i.e. to satisfy
security label rules) for reading or writing respectively.
The bit masks are indexed and manipulated as described in
.IR select (2).
.PP
At the same time, if the process has capability
.BR T_NOCHK 
(see
.IR getplab (2)),
all file descriptors indicated by ones among the first
.I nfd
bits of the previous values of 
.I readfds
and
.I writefds
are marked safe to read or write respectively.
.PP
Potentially unsafe situations arise from changes in file label caused
by this or other processes,
changes in process label, and file opening.
.PP
To prevent unintended violations of security policy,
programs with capability
.B NOCHK
must monitor label changes.
For this purpose the process label may be frozen (see
.IR getplab (2))
to prevent unintended automatic label changes.
.B SIGLAB
may be used to detect changes in file labels
(see
.IR signal (2)),
and
.I unsafe
to pinpoint them.
.SH DIAGNOSTICS
.B EFAULT
.SH SEE ALSO
.IR getflab (2),
.IR getplab (2),
.IR signal (2),
.IR select (2)