ABSEC/mod_absec.c

/* 
**  mod_absec.c -- Apache absec module
**  [base Autogenerated via ``apxs -n absec -g'']
**
**  To play with this sample module first compile it into a
**  DSO file and install it into Apache's modules directory 
**  by running:
**
**    $ apxs -lpam -lpam_misc -c -i mod_absec.c
**
**  Then activate it in Apache's httpd.conf file for instance
**  for the URL /absec in as follows:
**
**    #   httpd.conf
**    LoadModule absec_module modules/mod_absec.so
**    <Location /absec>
**    SetHandler absec
**    </Location>
**
**  Then after restarting Apache via
**
**    $ apachectl restart
**
*/ 

/*
    TEST URL
    http://10.211.55.15/absec/<fichier>
    
    INFORMATION SOURCES 

    https://apr.apache.org/docs/apr/1.5/group__apr__strings.html
    https://apr.apache.org/docs/apr-util/1.6/files.html

    https://httpd.apache.org/docs/2.4/developer/modguide.html
    http://www.ziviani.net/2011/how-to-create-an-apache-module

    https://en.wikipedia.org/wiki/Basic_access_authentication

*/

#include "httpd.h"
#include "http_config.h"
#include "http_core.h"
#include "http_protocol.h"
#include "ap_config.h"
#include "apr_base64.h"
#include "apr_strings.h"
#include "apr_portable.h"
#include "apr_user.h"

#include <pwd.h>
#include <grp.h>
#include <sys/types.h>
#include <unistd.h>
#include "apr_want.h"

#include <shadow.h>
#include <sys/stat.h>

#include "absec_pam.h"
#include "absec_mysql.h"

////////////////////////////////////////////////////////////////
/* Main routine - called after request processing */
static int absec_handler_last(request_rec *r)
{
    // Is this module really called?
    if (strcmp(r->handler, "absec")) {
        return DECLINED;
    }

    ////////
    /* http method validate the perm asked (r/w vs get/post,put) */
    ap_rprintf(r, "After Method: %s<br/>\r\n", r->method);
    int permmask = 0;
    if (strcmp(r->method,"GET")!=0)
    {
        // Not a GET, it's too late to do anything
        ap_rprintf(r, "Not a GET post treatement is too late!\n<br/>");
        return (DECLINED);
    }

    r->content_type = "text/html";      
    //ap_rprintf(r, "The sample page from mod_absec.c %s \n<br/>", r->args);
    ap_rprintf(r, "After GET Url: %s from %s \n<br/>", r->filename, r->uri);
    return (DECLINED);
}

////////////////////////////////////////////////////////////////
/* Main routine - called before request processing */
static int absec_handler_first(request_rec *r)
{
    ap_rprintf(r, "Before Method: %s<br/>\r\n", r->method);
    // Is this module really called?
    /*if (strcmp(r->handler, "absec")) {
        ap_rprintf(r, "DECLINED<br/>\r\n");
        return DECLINED;
    }*/


    ////////
    /* http method validate the perm asked (r/w vs get/post,put) */
    ap_rprintf(r, "Before Method: %s<br/>\r\n", r->method);

    int permmask = 0;
    if (strcmp(r->method,"GET")==0) permmask=0444;     // r
    if (strcmp(r->method,"PUT")==0) permmask=0222;     // w
    if (strcmp(r->method,"POST")==0) permmask=0222;    // w
    if (strcmp(r->method,"DELETE")==0) permmask=0111;  // x

    ////////
    /* check file permission on filesystem */
    /* should include <sys/stat.h> */
    struct stat fperm;
    int status;
    status = stat(r->filename, &fperm);
    //status = mysql_lookup(r, &fperm);
    //ap_rprintf(r, "Result mysql: %d<br/>\r\n", );
    if (status==-1) {
        ap_rprintf(r, "stat erreur %d", errno);
        return (OK);
    }
    //ap_rprintf(r, "File perms %o, owner %d, group %d (status %d)<br/>\r\n", fperm.st_mode, fperm.st_uid, fperm.st_gid, status);

    /* check if any permission (ogw) match method (get r, put/post w, delete x) */
    if ((fperm.st_mode & permmask)==0) {
        /* no permission match, return don't even have to check user perms */
        ap_rprintf(r, "Aucune permission pour la methode %s (%o, %o)", r->method, fperm.st_mode, permmask);
        return (OK);
    }

    // If file is world accessible for asked method return content
    if (fperm.st_mode & 0x7 & permmask) {
        /* if so, return, no need to check user perms */
        //ap_rprintf(r, "Fichier public<br/>\r\n");
        return (DECLINED);
    }

    ////////
    /* Check if we have a basic auth user */
    const char* auth64p;
    // Check if we have an auth header
    auth64p = apr_table_get(r->headers_in,"Authorization");

    // If no basic auth, ask for one
    if (auth64p==NULL) {
        r->content_type = "text/html";      
        apr_table_setn(r->err_headers_out,
                (PROXYREQ_PROXY == r->proxyreq) ? "Proxy-Authenticate"
                                                : "WWW-Authenticate",
                apr_pstrcat(r->pool, "Basic realm=\"PAS DE USER ", ap_auth_name(r),
                            "\"", NULL));
        return HTTP_UNAUTHORIZED;
    }

    ////////
    /* Retrieve user/pass from http basic auth header */
    // Get the basic auth base64 string and decode it
    // Start at char 6 to skip 'Basic '
    char *auth64;
    auth64 = apr_pstrdup(r->pool, auth64p+6);
    char *auth;
    auth = apr_pcalloc(r->pool, 64);
    apr_base64_decode(auth, auth64);
    char *user;
    char *pass;
    user = apr_strtok(auth, ":", &pass);

    r->content_type = "text/html";      
    ap_rprintf(r, "Url: %s from %s \n<br/>", r->filename, r->uri);
    //ap_rprintf(r, "Headers Authorization: %s \n<br/>", auth64);
    //ap_rprintf(r, "User/Pass: %s/%s \n<br/>", user, pass);
    
    int pam_result = pam_check_user(user, pass);
    if ( (pam_result==PAM_ERROR_START) || (pam_result==PAM_ERROR_STOP) ) {
        return HTTP_INTERNAL_SERVER_ERROR;
    }
    if (pam_result==PAM_ERROR_INVALID_CRED) {
        r->content_type = "text/html";      
        apr_table_setn(r->err_headers_out,
                (PROXYREQ_PROXY == r->proxyreq) ? "Proxy-Authenticate"
                                                : "WWW-Authenticate",
                apr_pstrcat(r->pool, "Basic realm=\"USER/PASS INVALIDE ", ap_auth_name(r),
                            "\"", NULL));
        return HTTP_UNAUTHORIZED;
    }

    ////////
    // Continue checking permission

    ////////
    /* Retrieve user details from /etc/passwd to get uid and primary group */
    /* Should include <pwd.h> */
    struct passwd *pw; 
    if((pw = getpwnam(user)) == NULL) 
    {
        // Should never happend as already verified with PAM
        ap_rprintf(r, "NULL \n<br/>");
        apr_table_setn(r->err_headers_out,
            (PROXYREQ_PROXY == r->proxyreq) ? "Proxy-Authenticate"
                                            : "WWW-Authenticate",
            apr_pstrcat(r->pool, "Basic realm=\"USER INCONNU ", ap_auth_name(r),
            "\"", NULL));
        // User cannot be found, unauthorized
        return HTTP_UNAUTHORIZED;
    }

    // If file is user readable and user match return content
    if ((fperm.st_uid==pw->pw_uid) && (fperm.st_mode & 0700 & permmask)) {
        ap_rprintf(r, "Fichier propriétaire<br/>\r\n");
        return (DECLINED);
    }

    // If file is group readable and primary group match return content
    if ((fperm.st_gid==pw->pw_gid) && (fperm.st_mode & 0070 & permmask)) {
        ap_rprintf(r, "Fichier groupe<br/>\r\n");
        return (DECLINED);
    }

    ////////
    /* Check supplemental groups */
    /* Should include <grp.h> */
    //ap_rprintf(r, "Fichier propriétaire %d %d %o %o<br/>\r\n", fperm.st_uid, i, fperm.st_mode, 0400);
    gid_t grouplist[16];
    int grouplistsize = 16;
    int groupreturn;
    groupreturn = getgrouplist(user, pw->pw_gid, grouplist, &grouplistsize);
    if (groupreturn >= 0) {
        ap_rprintf(r, "OK liste des groupes (%d)<br/>\r\n", grouplistsize);
        for (int i=0; i<grouplistsize; i++) {
            ap_rprintf(r, "group: %d\r\n", grouplist[i]);
            // If file is group readable and match a supplemental group return content
            if ((fperm.st_gid==grouplist[i]) && (fperm.st_mode & 0070 & permmask)) {
                ap_rprintf(r, "Fichier groupe supplementaire<br/>\r\n");
                return (DECLINED);
            }
        }
    }

    // else decline request
    ap_rprintf(r, "Aucuns droits de voir le fichier<br/>\r\n");
    apr_table_setn(r->err_headers_out,
            (PROXYREQ_PROXY == r->proxyreq) ? "Proxy-Authenticate"
                                            : "WWW-Authenticate",
            apr_pstrcat(r->pool, "Basic realm=\"NON AUTHORISE", ap_auth_name(r),
                        "\"", NULL));
    return HTTP_UNAUTHORIZED;

}

////////////////////////////////////////////////////////////////
static void absec_register_hooks(apr_pool_t *p)
{
    //ap_hook_handler(absec_handler, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_handler(absec_handler_last, NULL, NULL, APR_HOOK_LAST);
    ap_hook_handler(absec_handler_first, NULL, NULL, APR_HOOK_FIRST);

    // should use HOOK FIXUP

    // should use FILTER
}

////////////////////////////////////////////////////////////////
/* Dispatch list for API hooks */
module AP_MODULE_DECLARE_DATA absec_module = {
    STANDARD20_MODULE_STUFF, 
    NULL,                  /* create per-dir    config structures */
    NULL,                  /* merge  per-dir    config structures */
    NULL,                  /* create per-server config structures */
    NULL,                  /* merge  per-server config structures */
    NULL,                  /* table of config file commands       */
    absec_register_hooks  /* register hooks                      */
};