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Diffstat (limited to 'doc/man/pam_fail_delay.3')
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diff --git a/doc/man/pam_fail_delay.3 b/doc/man/pam_fail_delay.3 new file mode 100644 index 00000000..2e7e2f68 --- /dev/null +++ b/doc/man/pam_fail_delay.3 @@ -0,0 +1,368 @@ +.\" Title: pam_fail_delay +.\" Author: [FIXME: author] [see http://docbook.sf.net/el/author] +.\" Generator: DocBook XSL Stylesheets v1.74.0 <http://docbook.sf.net/> +.\" Date: 10/27/2010 +.\" Manual: Linux-PAM Manual +.\" Source: Linux-PAM Manual +.\" Language: English +.\" +.TH "PAM_FAIL_DELAY" "3" "10/27/2010" "Linux-PAM Manual" "Linux-PAM Manual" +.\" ----------------------------------------------------------------- +.\" * (re)Define some macros +.\" ----------------------------------------------------------------- +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.\" toupper - uppercase a string (locale-aware) +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.de toupper +.tr aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ +\\$* +.tr aabbccddeeffgghhiijjkkllmmnnooppqqrrssttuuvvwwxxyyzz +.. +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.\" SH-xref - format a cross-reference to an SH section +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.de SH-xref +.ie n \{\ +.\} +.toupper \\$* +.el \{\ +\\$* +.\} +.. +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.\" SH - level-one heading that works better for non-TTY output +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.de1 SH +.\" put an extra blank line of space above the head in non-TTY output +.if t \{\ +.sp 1 +.\} +.sp \\n[PD]u +.nr an-level 1 +.set-an-margin +.nr an-prevailing-indent \\n[IN] +.fi +.in \\n[an-margin]u +.ti 0 +.HTML-TAG ".NH \\n[an-level]" +.it 1 an-trap +.nr an-no-space-flag 1 +.nr an-break-flag 1 +\." make the size of the head bigger +.ps +3 +.ft B +.ne (2v + 1u) +.ie n \{\ +.\" if n (TTY output), use uppercase +.toupper \\$* +.\} +.el \{\ +.nr an-break-flag 0 +.\" if not n (not TTY), use normal case (not uppercase) +\\$1 +.in \\n[an-margin]u +.ti 0 +.\" if not n (not TTY), put a border/line under subheading +.sp -.6 +\l'\n(.lu' +.\} +.. +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.\" SS - level-two heading that works better for non-TTY output +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.de1 SS +.sp \\n[PD]u +.nr an-level 1 +.set-an-margin +.nr an-prevailing-indent \\n[IN] +.fi +.in \\n[IN]u +.ti \\n[SN]u +.it 1 an-trap +.nr an-no-space-flag 1 +.nr an-break-flag 1 +.ps \\n[PS-SS]u +\." make the size of the head bigger +.ps +2 +.ft B +.ne (2v + 1u) +.if \\n[.$] \&\\$* +.. +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.\" BB/BE - put background/screen (filled box) around block of text +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.de BB +.if t \{\ +.sp -.5 +.br +.in +2n +.ll -2n +.gcolor red +.di BX +.\} +.. +.de EB +.if t \{\ +.if "\\$2"adjust-for-leading-newline" \{\ +.sp -1 +.\} +.br +.di +.in +.ll +.gcolor +.nr BW \\n(.lu-\\n(.i +.nr BH \\n(dn+.5v +.ne \\n(BHu+.5v +.ie "\\$2"adjust-for-leading-newline" \{\ +\M[\\$1]\h'1n'\v'+.5v'\D'P \\n(BWu 0 0 \\n(BHu -\\n(BWu 0 0 -\\n(BHu'\M[] +.\} +.el \{\ +\M[\\$1]\h'1n'\v'-.5v'\D'P \\n(BWu 0 0 \\n(BHu -\\n(BWu 0 0 -\\n(BHu'\M[] +.\} +.in 0 +.sp -.5v +.nf +.BX +.in +.sp .5v +.fi +.\} +.. +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.\" BM/EM - put colored marker in margin next to block of text +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.de BM +.if t \{\ +.br +.ll -2n +.gcolor red +.di BX +.\} +.. +.de EM +.if t \{\ +.br +.di +.ll +.gcolor +.nr BH \\n(dn +.ne \\n(BHu +\M[\\$1]\D'P -.75n 0 0 \\n(BHu -(\\n[.i]u - \\n(INu - .75n) 0 0 -\\n(BHu'\M[] +.in 0 +.nf +.BX +.in +.fi +.\} +.. +.\" ----------------------------------------------------------------- +.\" * 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 +.fam C +.ps -1 +.nf +#include <security/pam_appl\&.h> +.fi +.fam +.ps +1 +.ft +.fam C +.HP \w'int\ pam_fail_delay('u +.BI "int pam_fail_delay(pam_handle_t\ *" "pamh" ", unsigned\ int\ " "usec" ");" +.fam +.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 25%) 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 +.\} +.fam C +.ps -1 +.nf +.if t \{\ +.sp -1 +.\} +.BB lightgray adjust-for-leading-newline +.sp -1 + +#ifdef HAVE_PAM_FAIL_DELAY + \&.\&.\&.\&. +#endif /* HAVE_PAM_FAIL_DELAY */ + +.EB lightgray adjust-for-leading-newline +.if t \{\ +.sp 1 +.\} +.fi +.fam +.ps +1 +.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 +.\} +.fam C +.ps -1 +.nf +.if t \{\ +.sp -1 +.\} +.BB lightgray adjust-for-leading-newline +.sp -1 + +void (*delay_fn)(int retval, unsigned usec_delay, void *appdata_ptr); + +.EB lightgray adjust-for-leading-newline +.if t \{\ +.sp 1 +.\} +.fi +.fam +.ps +1 +.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)\&. Note, if PAM_FAIL_DELAY item is unset (or set to NULL), then no delay will be performed\&. +.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 +.\} +.fam C +.ps -1 +.nf +.if t \{\ +.sp -1 +.\} +.BB lightgray adjust-for-leading-newline +.sp -1 + + pam_fail_delay (pamh, 3000000 /* micro\-seconds */ ); + pam_authenticate (pamh, 0); + +.EB lightgray adjust-for-leading-newline +.if t \{\ +.sp 1 +.\} +.fi +.fam +.ps +1 +.if n \{\ +.RE +.\} +.PP +if the modules do not request a delay, the failure delay will be between 2\&.25 and 3\&.75 seconds\&. +.PP +However, the modules, invoked in the authentication process, may also request delays: +.sp +.if n \{\ +.RS 4 +.\} +.fam C +.ps -1 +.nf +.if t \{\ +.sp -1 +.\} +.BB lightgray adjust-for-leading-newline +.sp -1 + +module #1: pam_fail_delay (pamh, 2000000); +module #2: pam_fail_delay (pamh, 4000000); + +.EB lightgray adjust-for-leading-newline +.if t \{\ +.sp 1 +.\} +.fi +.fam +.ps +1 +.if n \{\ +.RE +.\} +.PP +in this case, it is the largest requested value that is used to compute the actual failed delay: here between 3 and 5 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\&. |