From: Marco Trevisan (Treviño) <mail@xxxxxxxxx> PAM modules can change the user during their execution, in such case ssh would still use the user that has been provided giving potentially access to another user with the credentials of another one. So prevent this to happen, by ensuring that the final PAM user is matching the one that initiated the transaction. See also: https://github.com/util-linux/util-linux/pull/3206 --- auth-pam.c | 35 ++++++++++++++++++++++++++++++----- 1 file changed, 30 insertions(+), 5 deletions(-) diff --git a/auth-pam.c b/auth-pam.c index 13c0a792e..f45e61675 100644 --- a/auth-pam.c +++ b/auth-pam.c @@ -467,6 +467,28 @@ sshpam_thread_conv(int n, sshpam_const struct pam_message **msg, return (PAM_CONV_ERR); } +static int +check_pam_user(Authctxt *authctxt) +{ + const char *pam_user; + + if (authctxt == NULL || authctxt->user == NULL) + fatal("%s: PAM authctxt user not initialized", __func__); + + sshpam_err = pam_get_item(sshpam_handle, + PAM_USER, (sshpam_const void **) &pam_user); + if (sshpam_err != PAM_SUCCESS) + return sshpam_err; + + if (pam_user == NULL || strcmp(authctxt->user, pam_user) != 0) { + debug("PAM: User '%s' does not match expected '%s'", + pam_user, authctxt->user); + return PAM_USER_UNKNOWN; + } + + return PAM_SUCCESS; +} + /* * Authentication thread. */ @@ -521,6 +543,9 @@ sshpam_thread(void *ctxtp) sshpam_set_maxtries_reached(1); if (sshpam_err != PAM_SUCCESS) goto auth_fail; + sshpam_err = check_pam_user(sshpam_authctxt); + if (sshpam_err != PAM_SUCCESS) + goto auth_fail; if (!do_pam_account()) { sshpam_err = PAM_ACCT_EXPIRED; @@ -686,8 +711,7 @@ sshpam_cleanup(void) static int sshpam_init(struct ssh *ssh, Authctxt *authctxt) { - const char *pam_user, *user = authctxt->user; - const char **ptr_pam_user = &pam_user; + const char *user = authctxt->user; int r; if (options.pam_service_name == NULL) @@ -706,9 +730,8 @@ sshpam_init(struct ssh *ssh, Authctxt *authctxt) } if (sshpam_handle != NULL) { /* We already have a PAM context; check if the user matches */ - sshpam_err = pam_get_item(sshpam_handle, - PAM_USER, (sshpam_const void **)ptr_pam_user); - if (sshpam_err == PAM_SUCCESS && strcmp(user, pam_user) == 0) + sshpam_err = check_pam_user(authctxt); + if (sshpam_err == PAM_SUCCESS) return (0); pam_end(sshpam_handle, sshpam_err); sshpam_handle = NULL; @@ -1378,6 +1401,8 @@ sshpam_auth_passwd(Authctxt *authctxt, const char *password) sshpam_err = pam_authenticate(sshpam_handle, flags); sshpam_password = NULL; free(fake); + if (sshpam_err == PAM_SUCCESS) + sshpam_err = check_pam_user(authctxt); if (sshpam_err == PAM_MAXTRIES) sshpam_set_maxtries_reached(1); if (sshpam_err == PAM_SUCCESS && authctxt->valid) { -- 2.34.1 _______________________________________________ openssh-unix-dev mailing list openssh-unix-dev@xxxxxxxxxxx https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
