4 * Copyright (c) Andrew G. Morgan <morgan@kernel.org> 1996-9
12 * This is a simple implementation of a delay on failure mechanism; an
13 * attempt to overcome authentication-time attacks in a simple manner.
18 #include "pam_private.h"
20 /* **********************************************************************
21 * initialize the time as unset, this is set on the return from the
22 * authenticating pair of of the libpam pam_XXX calls.
25 void _pam_reset_timer(pam_handle_t *pamh)
27 D(("setting pamh->fail_delay.set to FALSE"));
28 pamh->fail_delay.set = PAM_FALSE;
31 /* **********************************************************************
32 * this function sets the start time for possible delayed failing.
34 * Eventually, it may set the timer so libpam knows how long the program
35 * has already been executing. Currently, this value is used to seed
36 * a pseudo-random number generator...
39 void _pam_start_timer(pam_handle_t *pamh)
41 pamh->fail_delay.begin = time(NULL);
42 D(("starting timer..."));
45 /* *******************************************************************
46 * Compute a pseudo random time. The value is base*(1 +/- 1/5) where
47 * the distribution is pseudo gausian (the sum of three evenly
48 * distributed random numbers -- central limit theorem and all ;^) The
49 * linear random numbers are based on a formulae given in Knuth's
50 * Seminumerical recipies that was reproduced in `Numerical Recipies
51 * in C'. It is *not* a cryptographically strong generator, but it is
52 * probably "good enough" for our purposes here.
54 * /dev/random might be a better place to look for some numbers...
57 static unsigned int _pam_rand(unsigned int seed)
64 static unsigned int _pam_compute_delay(unsigned int seed, unsigned int base)
70 for (sum=i=0; i<3; ++i) {
71 seed = _pam_rand(seed);
72 sum += (double) ((seed / 10) % 1000000);
74 sum = (sum/3.)/1e6 - .5; /* rescale */
75 ans = (unsigned int) ( base*(1.+sum) );
76 D(("random number: base=%u -> ans=%u\n", base, ans));
81 /* **********************************************************************
82 * the following function sleeps for a random time. The actual time
83 * slept is computed above.. It is based on the requested time but will
84 * differ by up to +/- 25%.
87 void _pam_await_timer(pam_handle_t *pamh, int status)
92 delay = _pam_compute_delay(pamh->fail_delay.begin,
93 pamh->fail_delay.delay);
94 if (pamh->fail_delay.delay_fn_ptr) {
97 void (*fn)(int, unsigned, void *);
101 if (pamh->pam_conversation) {
102 appdata_ptr = pamh->pam_conversation->appdata_ptr;
107 /* always call the applications delay function, even if
108 the delay is zero - indicate status */
109 hack_fn_u.value = pamh->fail_delay.delay_fn_ptr;
110 hack_fn_u.fn(status, delay, appdata_ptr);
112 } else if (status != PAM_SUCCESS && pamh->fail_delay.set) {
114 D(("will wait %u usec", delay));
119 tval.tv_sec = delay / 1000000;
120 tval.tv_usec = delay % 1000000;
121 select(0, NULL, NULL, NULL, &tval);
125 _pam_reset_timer(pamh);
129 /* **********************************************************************
130 * this function is known to both the module and the application, it
131 * keeps a running score of the largest-requested delay so far, as
132 * specified by either modules or an application.
135 int pam_fail_delay(pam_handle_t *pamh, unsigned int usec)
137 unsigned int largest;
139 IF_NO_PAMH("pam_fail_delay", pamh, PAM_SYSTEM_ERR);
141 D(("setting delay to %u",usec));
143 if (pamh->fail_delay.set) {
144 largest = pamh->fail_delay.delay;
146 pamh->fail_delay.set = PAM_TRUE;
150 D(("largest = %u",largest));
152 if (largest < usec) {
153 D(("resetting largest delay"));
154 pamh->fail_delay.delay = usec;