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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 14:22:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 14:22:51 +0000 |
commit | 9ada0093e92388590c7368600ca4e9e3e376f0d0 (patch) | |
tree | a56fe41110023676d7082028cbaa47ca4b6e6164 /doc/man/pam_fail_delay.3 | |
parent | Initial commit. (diff) | |
download | pam-9ada0093e92388590c7368600ca4e9e3e376f0d0.tar.xz pam-9ada0093e92388590c7368600ca4e9e3e376f0d0.zip |
Adding upstream version 1.5.2.upstream/1.5.2upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'doc/man/pam_fail_delay.3')
-rw-r--r-- | doc/man/pam_fail_delay.3 | 168 |
1 files changed, 168 insertions, 0 deletions
diff --git a/doc/man/pam_fail_delay.3 b/doc/man/pam_fail_delay.3 new file mode 100644 index 0000000..bbf2c36 --- /dev/null +++ b/doc/man/pam_fail_delay.3 @@ -0,0 +1,168 @@ +'\" t +.\" Title: pam_fail_delay +.\" Author: [FIXME: author] [see http://docbook.sf.net/el/author] +.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/> +.\" Date: 09/03/2021 +.\" Manual: Linux-PAM Manual +.\" Source: Linux-PAM Manual +.\" Language: English +.\" +.TH "PAM_FAIL_DELAY" "3" "09/03/2021" "Linux-PAM Manual" "Linux-PAM Manual" +.\" ----------------------------------------------------------------- +.\" * Define some portability stuff +.\" ----------------------------------------------------------------- +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.\" http://bugs.debian.org/507673 +.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.ie \n(.g .ds Aq \(aq +.el .ds Aq ' +.\" ----------------------------------------------------------------- +.\" * set default formatting +.\" ----------------------------------------------------------------- +.\" disable hyphenation +.nh +.\" disable justification (adjust text to left margin only) +.ad l +.\" ----------------------------------------------------------------- +.\" * MAIN CONTENT STARTS HERE * +.\" ----------------------------------------------------------------- +.SH "NAME" +pam_fail_delay \- request a delay on failure +.SH "SYNOPSIS" +.sp +.ft B +.nf +#include <security/pam_appl\&.h> +.fi +.ft +.HP \w'int\ pam_fail_delay('u +.BI "int pam_fail_delay(pam_handle_t\ *" "pamh" ", unsigned\ int\ " "usec" ");" +.SH "DESCRIPTION" +.PP +The +\fBpam_fail_delay\fR +function provides a mechanism by which an application or module can suggest a minimum delay of +\fIusec\fR +micro\-seconds\&. The function keeps a record of the longest time requested with this function\&. Should +\fBpam_authenticate\fR(3) +fail, the failing return to the application is delayed by an amount of time randomly distributed (by up to 50%) about this longest value\&. +.PP +Independent of success, the delay time is reset to its zero default value when the PAM service module returns control to the application\&. The delay occurs +\fIafter\fR +all authentication modules have been called, but +\fIbefore\fR +control is returned to the service application\&. +.PP +When using this function the programmer should check if it is available with: +.sp +.if n \{\ +.RS 4 +.\} +.nf +#ifdef HAVE_PAM_FAIL_DELAY + \&.\&.\&.\&. +#endif /* HAVE_PAM_FAIL_DELAY */ + +.fi +.if n \{\ +.RE +.\} +.PP +For applications written with a single thread that are event driven in nature, generating this delay may be undesirable\&. Instead, the application may want to register the delay in some other way\&. For example, in a single threaded server that serves multiple authentication requests from a single event loop, the application might want to simply mark a given connection as blocked until an application timer expires\&. For this reason the delay function can be changed with the +\fIPAM_FAIL_DELAY\fR +item\&. It can be queried and set with +\fBpam_get_item\fR(3) +and +\fBpam_set_item\fR(3) +respectively\&. The value used to set it should be a function pointer of the following prototype: +.sp +.if n \{\ +.RS 4 +.\} +.nf +void (*delay_fn)(int retval, unsigned usec_delay, void *appdata_ptr); + +.fi +.if n \{\ +.RE +.\} +.sp +The arguments being the +\fIretval\fR +return code of the module stack, the +\fIusec_delay\fR +micro\-second delay that libpam is requesting and the +\fIappdata_ptr\fR +that the application has associated with the current +\fIpamh\fR\&. This last value was set by the application when it called +\fBpam_start\fR(3) +or explicitly with +\fBpam_set_item\fR(3)\&. +.PP +Note that the PAM_FAIL_DELAY item is set to NULL by default\&. This indicates that PAM should perform a random delay as described above when authentication fails and a delay has been suggested\&. If an application does not want the PAM library to perform any delay on authentication failure, then the application must define a custom delay function that executes no statements and set the PAM_FAIL_DELAY item to point to this function\&. +.SH "RATIONALE" +.PP +It is often possible to attack an authentication scheme by exploiting the time it takes the scheme to deny access to an applicant user\&. In cases of +\fIshort\fR +timeouts, it may prove possible to attempt a +\fIbrute force\fR +dictionary attack \-\- with an automated process, the attacker tries all possible passwords to gain access to the system\&. In other cases, where individual failures can take measurable amounts of time (indicating the nature of the failure), an attacker can obtain useful information about the authentication process\&. These latter attacks make use of procedural delays that constitute a +\fIcovert channel\fR +of useful information\&. +.PP +To minimize the effectiveness of such attacks, it is desirable to introduce a random delay in a failed authentication process\&. Preferable this value should be set by the application or a special PAM module\&. Standard PAM modules should not modify the delay unconditional\&. +.SH "EXAMPLE" +.PP +For example, a login application may require a failure delay of roughly 3 seconds\&. It will contain the following code: +.sp +.if n \{\ +.RS 4 +.\} +.nf + pam_fail_delay (pamh, 3000000 /* micro\-seconds */ ); + pam_authenticate (pamh, 0); + +.fi +.if n \{\ +.RE +.\} +.PP +if the modules do not request a delay, the failure delay will be between 1\&.5 and 4\&.5 seconds\&. +.PP +However, the modules, invoked in the authentication process, may also request delays: +.sp +.if n \{\ +.RS 4 +.\} +.nf +module #1: pam_fail_delay (pamh, 2000000); +module #2: pam_fail_delay (pamh, 4000000); + +.fi +.if n \{\ +.RE +.\} +.PP +in this case, it is the largest requested value that is used to compute the actual failed delay: here between 2 and 6 seconds\&. +.SH "RETURN VALUES" +.PP +PAM_SUCCESS +.RS 4 +Delay was successful adjusted\&. +.RE +.PP +PAM_SYSTEM_ERR +.RS 4 +A NULL pointer was submitted as PAM handle\&. +.RE +.SH "SEE ALSO" +.PP +\fBpam_start\fR(3), +\fBpam_get_item\fR(3), +\fBpam_strerror\fR(3) +.SH "STANDARDS" +.PP +The +\fBpam_fail_delay\fR +function is an Linux\-PAM extension\&. |