Initial commit.

.gitignore

@@ -1,3 +1,6 @@
+checkpw
+checkpw_interactive
+
 # ---> C
 # Prerequisites
 *.d

README.md

@@ -1,3 +1,14 @@
 # checkpw
 
-checkpw is a program to check the validity of a user password on a Linux/PAM-based system.
+checkpw is a program to check the validity of a users password on a Linux/PAM-based system.
+
+# Installation:
+
+gcc -lpam -lpam_misc -o checkpw checkpw.c
+
+# Usage:
+
+./checkpw -u $USERNAME -p $PASSWORD
+
+echo $?
+

checkpw.c

@@ -0,0 +1,122 @@
+/*
+ * checkpw is a program to check the validity of a user password on a
+ * Linux/PAM-based system.
+ *
+ * Usage: checkpw -u $USER -p $PASSWORD
+ *
+ * Returns 0 on success, 1 otherwise.
+ */
+
+#include <security/pam_appl.h>
+#include <security/pam_misc.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define MAX_USERNAME_LEN 32
+#define MAX_PASSWORD_LEN 256
+
+// Custom data structure to hold user-entered password
+struct pam_credentials {
+    const char *password;
+};
+
+// PAM conversation function to supply the password
+int pam_conversation(int num_msg, const struct pam_message **msg,
+                     struct pam_response **resp, void *appdata_ptr) {
+
+    struct pam_response *response = NULL;
+    struct pam_credentials *credentials = (struct pam_credentials *)appdata_ptr;
+    int i;
+
+    response = (struct pam_response *)malloc(sizeof(struct pam_response) * num_msg);
+    if (response == NULL) {
+        return PAM_CONV_ERR;
+    }
+
+    for (i = 0; i < num_msg; i++) {
+        if (msg[i]->msg_style == PAM_PROMPT_ECHO_OFF || msg[i]->msg_style == PAM_PROMPT_ECHO_ON) {
+            response[i].resp = strdup(credentials->password);
+            response[i].resp_retcode = 0;
+        }
+    }
+
+    *resp = response;
+    return PAM_SUCCESS;
+}
+
+int authenticate(const char *username, const char *password) {
+
+    pam_handle_t *pamh = NULL;
+    int retval;
+    struct pam_credentials credentials = { password };
+    struct pam_conv conv = { pam_conversation, &credentials };
+
+    retval = pam_start("login", username, &conv, &pamh);
+
+    if (retval == PAM_SUCCESS) {
+        retval = pam_authenticate(pamh, 0); // Attempt to authenticate
+    }
+
+    if (retval == PAM_SUCCESS) {
+        retval = pam_acct_mgmt(pamh, 0); // Check account validity
+    }
+
+    if (pam_end(pamh, retval) != PAM_SUCCESS) {
+        pamh = NULL;
+        fprintf(stderr, "Failed to release PAM authenticator\n");
+        exit(1);
+    }
+
+    return (retval == PAM_SUCCESS ? 0 : 1); // 0 for success, 1 for failure
+}
+
+int main(int argc, char *argv[]) {
+
+    char username[MAX_USERNAME_LEN];
+    char password[MAX_PASSWORD_LEN];
+    int opt;
+
+    memset(username, 0, sizeof(username));
+    memset(password, 0, sizeof(password));
+
+    // Parse command-line arguments
+    while ((opt = getopt(argc, argv, "u:p:")) != -1) {
+        switch (opt) {
+            case 'u':
+                if (strlen(optarg) >= MAX_USERNAME_LEN) {
+                    fprintf(stderr, "Error: Username is too long (maximum %d characters).\n", MAX_USERNAME_LEN);
+                    exit(1);
+                }
+                strncpy(username, optarg, MAX_USERNAME_LEN - 1);
+                break;
+            case 'p':
+                if (strlen(optarg) >= MAX_PASSWORD_LEN) {
+                    fprintf(stderr, "Error: Password is too long (maximum %d characters).\n", MAX_PASSWORD_LEN);
+                    exit(1);
+                }
+                strncpy(password, optarg, MAX_PASSWORD_LEN - 1);
+                break;
+            default:
+                fprintf(stderr, "Usage: %s -u <username> -p <password>\n", argv[0]);
+                exit(1);
+        }
+    }
+
+    // Check if both username and password are provided
+    if (username[0] == '\0' || password[0] == '\0') {
+        fprintf(stderr, "Usage: %s -u <username> -p <password>\n", argv[0]);
+        exit(1);
+    }
+
+    // Authenticate the user
+    if (authenticate(username, password) == 0) {
+        printf("Authenticated successfully.\n");
+        return 0;
+    } else {
+        printf("Authentication failed.\n");
+        return 1;
+    }
+}
+