diff options
Diffstat (limited to 'libpam/pam_delay.c')
| -rw-r--r-- | libpam/pam_delay.c | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/libpam/pam_delay.c b/libpam/pam_delay.c new file mode 100644 index 0000000..549da89 --- /dev/null +++ b/libpam/pam_delay.c @@ -0,0 +1,160 @@ +/* + * pam_delay.c + * + * Copyright (c) Andrew G. Morgan <morgan@kernel.org> 1996-9 + * All rights reserved. + * + * $Id$ + * + */ + +/* + * This is a simple implementation of a delay on failure mechanism; an + * attempt to overcome authentication-time attacks in a simple manner. + */ + +#include "pam_private.h" +#include <unistd.h> +#include <time.h> + +/* ********************************************************************** + * initialize the time as unset, this is set on the return from the + * authenticating pair of of the libpam pam_XXX calls. + */ + +void _pam_reset_timer(pam_handle_t *pamh) +{ + D(("setting pamh->fail_delay.set to FALSE")); + pamh->fail_delay.set = PAM_FALSE; +} + +/* ********************************************************************** + * this function sets the start time for possible delayed failing. + * + * Eventually, it may set the timer so libpam knows how long the program + * has already been executing. Currently, this value is used to seed + * a pseudo-random number generator... + */ + +void _pam_start_timer(pam_handle_t *pamh) +{ + pamh->fail_delay.begin = time(NULL); + D(("starting timer...")); +} + +/* ******************************************************************* + * Compute a pseudo random time. The value is base*(1 +/- 1/5) where + * the distribution is pseudo gaussian (the sum of three evenly + * distributed random numbers -- central limit theorem and all ;^) The + * linear random numbers are based on a formulae given in Knuth's + * Seminumerical recipes that was reproduced in `Numerical Recipes + * in C'. It is *not* a cryptographically strong generator, but it is + * probably "good enough" for our purposes here. + * + * /dev/random might be a better place to look for some numbers... + */ + +static unsigned int _pam_rand(unsigned int seed) +{ +#define N1 1664525 +#define N2 1013904223 + return N1*seed + N2; +} + +static unsigned int _pam_compute_delay(unsigned int seed, unsigned int base) +{ + int i; + double sum; + unsigned int ans; + + for (sum=i=0; i<3; ++i) { + seed = _pam_rand(seed); + sum += (double) ((seed / 10) % 1000000); + } + sum = (sum/3.)/1e6 - .5; /* rescale */ + ans = (unsigned int) ( base*(1.+sum) ); + D(("random number: base=%u -> ans=%u\n", base, ans)); + + return ans; +} + +/* ********************************************************************** + * By default, the following function sleeps for a random time. The + * actual time slept is computed above. It is based on the requested + * time but will differ by up to +/- 50%. If the PAM_FAIL_DELAY item is + * set by the client, this function will call the function referenced by + * that item, overriding the default behavior. + */ + +void _pam_await_timer(pam_handle_t *pamh, int status) +{ + unsigned int delay; + D(("waiting?...")); + + delay = _pam_compute_delay(pamh->fail_delay.begin, + pamh->fail_delay.delay); + if (pamh->fail_delay.delay_fn_ptr) { + union { + const void *value; + void (*fn)(int, unsigned, void *); + } hack_fn_u; + void *appdata_ptr; + + if (pamh->pam_conversation) { + appdata_ptr = pamh->pam_conversation->appdata_ptr; + } else { + appdata_ptr = NULL; + } + + /* always call the applications delay function, even if + the delay is zero - indicate status */ + hack_fn_u.value = pamh->fail_delay.delay_fn_ptr; + hack_fn_u.fn(status, delay, appdata_ptr); + + } else if (status != PAM_SUCCESS && pamh->fail_delay.set) { + + D(("will wait %u usec", delay)); + + if (delay > 0) { + struct timeval tval; + + tval.tv_sec = delay / 1000000; + tval.tv_usec = delay % 1000000; + select(0, NULL, NULL, NULL, &tval); + } + } + + _pam_reset_timer(pamh); + D(("waiting done")); +} + +/* ********************************************************************** + * this function is known to both the module and the application, it + * keeps a running score of the largest-requested delay so far, as + * specified by either modules or an application. + */ + +int pam_fail_delay(pam_handle_t *pamh, unsigned int usec) +{ + unsigned int largest; + + IF_NO_PAMH("pam_fail_delay", pamh, PAM_SYSTEM_ERR); + + D(("setting delay to %u",usec)); + + if (pamh->fail_delay.set) { + largest = pamh->fail_delay.delay; + } else { + pamh->fail_delay.set = PAM_TRUE; + largest = 0; + } + + D(("largest = %u",largest)); + + if (largest < usec) { + D(("resetting largest delay")); + pamh->fail_delay.delay = usec; + } + + return PAM_SUCCESS; +} |