src/auth/passdb-pam.c

	passdb-pam.c revision 49e513d090753ccbf95560b2f3a21f081a5b6c51
/*
   Based on auth_pam.c from popa3d by Solar Designer <solar@openwall.com>.

   You're allowed to do whatever you like with this software (including
   re-distribution in source and/or binary form, with or without
   modification), provided that credit is given where it is due and any
   modified versions are marked as such.  There's absolutely no warranty.
*/

#include "config.h"
#undef HAVE_CONFIG_H

#ifdef PASSDB_PAM

#include "common.h"
#include "buffer.h"
#include "ioloop.h"
#include "network.h"
#include "passdb.h"
#include "mycrypt.h"
#include "safe-memset.h"

#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/wait.h>

#ifdef HAVE_SECURITY_PAM_APPL_H
#  include <security/pam_appl.h>
#elif defined(HAVE_PAM_PAM_APPL_H)
#  include <pam/pam_appl.h>
#endif

#if !defined(_SECURITY_PAM_APPL_H) && !defined(LINUX_PAM) && !defined(_OPENPAM)
/* Sun's PAM doesn't use const. we use a bit dirty hack to check it.
   Originally it was just __sun__ check, but HP/UX also uses Sun's PAM
   so I thought this might work better. */
#  define linux_const
#else
#  define linux_const           const
#endif
typedef linux_const void *pam_item_t;

#ifdef AUTH_PAM_USERPASS
#  include <security/pam_client.h>

#  ifndef PAM_BP_RCONTROL
/* Linux-PAM prior to 0.74 */
#    define PAM_BP_RCONTROL PAM_BP_CONTROL
#    define PAM_BP_WDATA    PAM_BP_DATA
#    define PAM_BP_RDATA    PAM_BP_DATA
#  endif

#  define USERPASS_AGENT_ID     "userpass"
#  define USERPASS_AGENT_ID_LENGTH  8

#  define USERPASS_USER_MASK        0x03
#  define USERPASS_USER_REQUIRED    1
#  define USERPASS_USER_KNOWN       2
#  define USERPASS_USER_FIXED       3
#endif

struct pam_auth_request {
    int fd;
    struct io *io;

    struct auth_request *request;
        verify_plain_callback_t *callback;
};

struct pam_userpass {
    const char *user;
    const char *pass;
};

static char *service_name;
static struct timeout *to_wait;

static int pam_userpass_conv(int num_msg, linux_const struct pam_message **msg,
    struct pam_response **resp, void *appdata_ptr)
{
    /* @UNSAFE */
    struct pam_userpass *userpass = (struct pam_userpass *) appdata_ptr;
#ifdef AUTH_PAM_USERPASS
    pamc_bp_t prompt;
    const char *input;
    char *output;
    char flags;
    size_t userlen, passlen;

    if (num_msg != 1 || msg[0]->msg_style != PAM_BINARY_PROMPT)
        return PAM_CONV_ERR;

    prompt = (pamc_bp_t)msg[0]->msg;
    input = PAM_BP_RDATA(prompt);

    if (PAM_BP_RCONTROL(prompt) != PAM_BPC_SELECT ||
        strncmp(input, USERPASS_AGENT_ID "/", USERPASS_AGENT_ID_LENGTH + 1))
        return PAM_CONV_ERR;

    flags = input[USERPASS_AGENT_ID_LENGTH + 1];
    input += USERPASS_AGENT_ID_LENGTH + 1 + 1;

    if ((flags & USERPASS_USER_MASK) == USERPASS_USER_FIXED &&
        strcmp(input, userpass->user))
        return PAM_CONV_AGAIN;

    if (!(*resp = malloc(sizeof(struct pam_response))))
        return PAM_CONV_ERR;

    userlen = strlen(userpass->user);
    passlen = strlen(userpass->pass);

    prompt = NULL;
    PAM_BP_RENEW(&prompt, PAM_BPC_DONE, userlen + 1 + passlen);
    output = PAM_BP_WDATA(prompt);

    memcpy(output, userpass->user, userlen + 1);
    memcpy(output + userlen + 1, userpass->pass, passlen);

    (*resp)[0].resp_retcode = 0;
    (*resp)[0].resp = (char *)prompt;
#else
    char *string;
    int i;

    if (!(*resp = malloc(num_msg * sizeof(struct pam_response))))
        return PAM_CONV_ERR;

    for (i = 0; i < num_msg; i++) {
        switch (msg[i]->msg_style) {
        case PAM_PROMPT_ECHO_ON:
            string = strdup(userpass->user);
            if (string == NULL)
                i_fatal("Out of memory");
            break;
        case PAM_PROMPT_ECHO_OFF:
            string = strdup(userpass->pass);
            if (string == NULL)
                i_fatal("Out of memory");
            break;
        case PAM_ERROR_MSG:
        case PAM_TEXT_INFO:
            string = NULL;
            break;
        default:
            while (--i >= 0) {
                if ((*resp)[i].resp == NULL)
                    continue;
                safe_memset((*resp)[i].resp, 0,
                        strlen((*resp)[i].resp));
                free((*resp)[i].resp);
                (*resp)[i].resp = NULL;
            }

            free(*resp);
            *resp = NULL;

            return PAM_CONV_ERR;
        }

        (*resp)[i].resp_retcode = PAM_SUCCESS;
        (*resp)[i].resp = string;
    }
#endif

    return PAM_SUCCESS;
}

static int pam_auth(pam_handle_t *pamh, const char **error)
{
    void *item;
    int status;

    *error = NULL;

    if ((status = pam_authenticate(pamh, 0)) != PAM_SUCCESS) {
        *error = t_strdup_printf("pam_authenticate() failed: %s",
                     pam_strerror(pamh, status));
        return status;
    }

#ifdef HAVE_PAM_SETCRED
    if ((status = pam_setcred(pamh, PAM_ESTABLISH_CRED)) != PAM_SUCCESS) {
        *error = t_strdup_printf("pam_setcred() failed: %s",
                     pam_strerror(pamh, status));
        return status;
    }
#endif

    if ((status = pam_acct_mgmt(pamh, 0)) != PAM_SUCCESS) {
        *error = t_strdup_printf("pam_acct_mgmt() failed: %s",
                     pam_strerror(pamh, status));
        return status;
    }

    status = pam_get_item(pamh, PAM_USER, (linux_const void **)&item);
    if (status != PAM_SUCCESS) {
        *error = t_strdup_printf("pam_get_item() failed: %s",
                     pam_strerror(pamh, status));
        return status;
    }

    return PAM_SUCCESS;
}

static void
pam_verify_plain_child(const struct auth_request *request, const char *service,
               const char *password, int fd)
{
    pam_handle_t *pamh;
    struct pam_userpass userpass;
    struct pam_conv conv;
    enum passdb_result result;
    int status, status2;
    const char *str;
    char buf_data[512];
    buffer_t *buf;

    conv.conv = pam_userpass_conv;
    conv.appdata_ptr = &userpass;

    userpass.user = request->user;
    userpass.pass = password;

    status = pam_start(service, request->user, &conv, &pamh);
    if (status != PAM_SUCCESS) {
        result = PASSDB_RESULT_INTERNAL_FAILURE;
        str = t_strdup_printf("pam_start() failed: %s",
                      pam_strerror(pamh, status));
    } else {
#ifdef PAM_RHOST
        const char *host = net_ip2addr(&request->remote_ip);
        if (host != NULL)
            pam_set_item(pamh, PAM_RHOST, host);
#endif

        status = pam_auth(pamh, &str);
        if ((status2 = pam_end(pamh, status)) == PAM_SUCCESS) {
            /* FIXME: check for PASSDB_RESULT_UNKNOWN_USER
               somehow? */
            result = status == PAM_SUCCESS ? PASSDB_RESULT_OK :
                PASSDB_RESULT_PASSWORD_MISMATCH;
        } else {
            result = PASSDB_RESULT_INTERNAL_FAILURE;
            str = t_strdup_printf("pam_end() failed: %s",
                          pam_strerror(pamh, status2));
        }
    }

    buf = buffer_create_data(pool_datastack_create(),
                 buf_data, sizeof(buf_data));
    buffer_append(buf, &result, sizeof(result));

    if (str != NULL) {
        /* may truncate the error. tough luck. */
        buffer_append(buf, str, strlen(str));
    }

    write(fd, buf_data, buffer_get_used_size(buf));
}

static void pam_child_input(void *context)
{
    struct pam_auth_request *request = context;
    struct auth_request *auth_request = request->request;
    enum passdb_result result;
    char buf[513];
    ssize_t ret;

    /* POSIX guarantees that writing 512 bytes or less to pipes is atomic.
       We rely on that. */
    ret = read(request->fd, buf, sizeof(buf)-1);
    if (ret < 0) {
        auth_request_log_error(auth_request, "pam",
                       "read() from child process failed: %m");
        result = PASSDB_RESULT_INTERNAL_FAILURE;
    } else if (ret == 0) {
        /* it died */
        auth_request_log_error(auth_request, "pam",
                       "Child process died");
        result = PASSDB_RESULT_INTERNAL_FAILURE;
    } else if ((size_t)ret < sizeof(result)) {
        auth_request_log_error(auth_request, "pam",
            "Child process returned only %d bytes", ret);
        result = PASSDB_RESULT_INTERNAL_FAILURE;
    } else {
        memcpy(&result, buf, sizeof(result));

        if ((size_t)ret > sizeof(result)) {
            /* error message included */
            buf[ret] = '\0';

            if (result == PASSDB_RESULT_INTERNAL_FAILURE) {
                auth_request_log_error(auth_request, "pam",
                    "%s", buf + sizeof(result));
            } else {
                auth_request_log_info(auth_request, "pam",
                    "%s", buf + sizeof(result));
            }
        }
    }

    if (close(request->fd) < 0) {
        auth_request_log_error(auth_request, "pam",
                       "close(child input) failed: %m");
    }

    if (auth_request_unref(auth_request))
        request->callback(result, auth_request);

    io_remove(request->io);
    i_free(request);
}

static void wait_timeout(void *context __attr_unused__)
{
    int status;
    pid_t pid;

    /* FIXME: if we ever do some other kind of forking, this needs fixing */
    while ((pid = waitpid(-1, &status, WNOHANG)) != 0) {
        if (pid == -1) {
            if (errno == ECHILD) {
                timeout_remove(to_wait);
                to_wait = NULL;
            } else if (errno != EINTR)
                i_error("waitpid() failed: %m");
            return;
        }

        if (WIFSIGNALED(status)) {
            i_error("PAM: Child %s died with signal %d",
                dec2str(pid), WTERMSIG(status));
        }
    }
}

static void
pam_verify_plain(struct auth_request *request, const char *password,
         verify_plain_callback_t *callback)
{
        struct pam_auth_request *pam_auth_request;
    const char *service;
    int fd[2];
    pid_t pid;

    service = service_name != NULL ? service_name : request->service;
    if (pipe(fd) < 0) {
        auth_request_log_error(request, "pam", "pipe() failed: %m");
        callback(PASSDB_RESULT_INTERNAL_FAILURE, request);
        return;
    }

    pid = fork();
    if (pid == -1) {
        auth_request_log_error(request, "pam", "fork() failed: %m");
        callback(PASSDB_RESULT_INTERNAL_FAILURE, request);
        (void)close(fd[0]);
        (void)close(fd[1]);
        return;
    }

    if (pid == 0) {
        (void)close(fd[0]);
        pam_verify_plain_child(request, service, password, fd[1]);
        _exit(0);
    }

    if (close(fd[1]) < 0) {
        auth_request_log_error(request, "pam",
                       "close(fd[1]) failed: %m");
    }

    auth_request_ref(request);
    pam_auth_request = i_new(struct pam_auth_request, 1);
    pam_auth_request->fd = fd[0];
    pam_auth_request->request = request;
    pam_auth_request->callback = callback;

    pam_auth_request->io =
        io_add(fd[0], IO_READ, pam_child_input, pam_auth_request);

    if (to_wait == NULL)
        to_wait = timeout_add(1000, wait_timeout, NULL);
}

static void pam_init(const char *args)
{
    service_name = strcmp(args, "*") == 0 ? NULL :
        i_strdup(*args != '\0' ? args : "dovecot");
    to_wait = NULL;
}

static void pam_deinit(void)
{
    if (to_wait != NULL)
        timeout_remove(to_wait);
    i_free(service_name);
}

struct passdb_module passdb_pam = {
    "pam",

    NULL,
    pam_init,
    pam_deinit,

    pam_verify_plain,
    NULL
};

#endif