From: Marco Trevisan (Treviño) <mail@3v1n0.net>
Date: Fri, 20 Sep 2024 15:23:16 +0000 (+0200)
Subject: login-utils/su-common: Check that the user didn't change during PAM transaction
X-Git-Tag: v2.42-start~194^2
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d6564701e81254064ace56b57e6090620ed29d28;p=thirdparty%2Futil-linux.git

login-utils/su-common: Check that the user didn't change during PAM transaction

PAM modules can change the user during their execution, in such case su
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 required
---

diff --git a/login-utils/su-common.c b/login-utils/su-common.c
index 12c933633..844d1d431 100644
--- a/login-utils/su-common.c
+++ b/login-utils/su-common.c
@@ -382,6 +382,7 @@ static void supam_export_environment(struct su_context *su)
 static void supam_authenticate(struct su_context *su)
 {
 	const char *srvname = NULL;
+	const char *pam_user = NULL;
 	int rc;
 
 	srvname = su->runuser ?
@@ -422,6 +423,16 @@ static void supam_authenticate(struct su_context *su)
 	rc = pam_acct_mgmt(su->pamh, 0);
 	if (rc == PAM_NEW_AUTHTOK_REQD)
 		rc = pam_chauthtok(su->pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
+
+	rc = pam_get_item(su->pamh, PAM_USER, (const void **) &pam_user);
+	if (is_pam_failure(rc))
+		goto done;
+
+	if (pam_user == NULL || strcmp(pam_user, su->pwd->pw_name) != 0) {
+		rc = PAM_USER_UNKNOWN;
+		goto done;
+	}
+
  done:
 	log_syslog(su, !is_pam_failure(rc));