From b4708e0dbdf30b7fb41e457540bd98aaeb0e3aac Mon Sep 17 00:00:00 2001
From: Matt Hunter <m@lfurio.us>
Date: Sat, 17 Jan 2026 17:40:44 -0500
Subject: patch: pam auth

Replaces shadow support with PAM authentication support.

Change variable pam_service in config.def.h to the corresponding PAM
service.  The default configuration is for ArchLinux's login service.
---
 config.def.h |  4 ++++
 config.mk    |  2 +-
 slock.c      | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++-------
 3 files changed, 61 insertions(+), 8 deletions(-)

diff --git a/config.def.h b/config.def.h
index c99dbf5..ba37a59 100644
--- a/config.def.h
+++ b/config.def.h
@@ -7,6 +7,7 @@ static const char *colorname[NUMCOLS] = {
 	[INPUT] =  "#005577",   /* during input */
 	[FAILED] = "#CC3333",   /* wrong password */
 	[CAPS] = "red",         /* CapsLock on */
+	[PAM] =    "#9400D3",   /* waiting for PAM */
 };
 
 /* treat a cleared input like a wrong password (color) */
@@ -17,3 +18,6 @@ static const int controlkeyclear = 1;
 
 /* time in seconds before the monitor shuts down */
 static const int monitortime = 7;
+
+/* PAM service that's used for authentication */
+static const char* pam_service = "login";
diff --git a/config.mk b/config.mk
index dcd27d0..69f6e09 100644
--- a/config.mk
+++ b/config.mk
@@ -12,7 +12,7 @@ X11LIB = /usr/X11R6/lib
 
 # includes and libs
 INCS = -I. -I/usr/include -I${X11INC}
-LIBS = -L/usr/lib -lc -lcrypt -L${X11LIB} -lX11 -lXext -lXrandr
+LIBS = -L/usr/lib -lc -lcrypt -L${X11LIB} -lX11 -lXext -lXrandr -lpam
 
 # flags
 CPPFLAGS = -DVERSION=\"${VERSION}\" -D_DEFAULT_SOURCE -DHAVE_SHADOW_H
diff --git a/slock.c b/slock.c
index 1a19d5f..8628bf3 100644
--- a/slock.c
+++ b/slock.c
@@ -21,17 +21,23 @@
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 #include <X11/XKBlib.h>
+#include <security/pam_appl.h>
+#include <security/pam_misc.h>
 
 #include "arg.h"
 #include "util.h"
 
 char *argv0;
+static int pam_conv(int num_msg, const struct pam_message **msg, struct pam_response **resp, void *appdata_ptr);
+struct pam_conv pamc = {pam_conv, NULL};
+char passwd[256];
 
 enum {
 	INIT,
 	INPUT,
 	FAILED,
 	CAPS,
+	PAM,
 	NUMCOLS
 };
 
@@ -61,6 +67,31 @@ die(const char *errstr, ...)
 	exit(1);
 }
 
+static int
+pam_conv(int num_msg, const struct pam_message **msg,
+		struct pam_response **resp, void *appdata_ptr)
+{
+	int retval = PAM_CONV_ERR;
+	for(int i=0; i<num_msg; i++) {
+		if (msg[i]->msg_style == PAM_PROMPT_ECHO_OFF &&
+				strncmp(msg[i]->msg, "Password: ", 10) == 0) {
+			struct pam_response *resp_msg = malloc(sizeof(struct pam_response));
+			if (!resp_msg)
+				die("malloc failed\n");
+			char *password = malloc(strlen(passwd) + 1);
+			if (!password)
+				die("malloc failed\n");
+			memset(password, 0, strlen(passwd) + 1);
+			strcpy(password, passwd);
+			resp_msg->resp_retcode = 0;
+			resp_msg->resp = password;
+			resp[i] = resp_msg;
+			retval = PAM_SUCCESS;
+		}
+	}
+	return retval;
+}
+
 #ifdef __linux__
 #include <fcntl.h>
 #include <linux/oom.h>
@@ -125,6 +156,8 @@ gethash(void)
 	}
 #endif /* HAVE_SHADOW_H */
 
+	/* pam, store user name */
+	hash = pw->pw_name;
 	return hash;
 }
 
@@ -133,11 +166,12 @@ readpw(Display *dpy, struct xrandr *rr, struct lock **locks, int nscreens,
        const char *hash)
 {
 	XRRScreenChangeNotifyEvent *rre;
-	char buf[32], passwd[256], *inputhash;
-	int caps, num, screen, running, failure, oldc;
+	char buf[32];
+	int caps, num, screen, running, failure, oldc, retval;
 	unsigned int len, color, indicators;
 	KeySym ksym;
 	XEvent ev;
+	pam_handle_t *pamh;
 
 	len = 0;
 	caps = 0;
@@ -168,10 +202,26 @@ readpw(Display *dpy, struct xrandr *rr, struct lock **locks, int nscreens,
 			case XK_Return:
 				passwd[len] = '\0';
 				errno = 0;
-				if (!(inputhash = crypt(passwd, hash)))
-					fprintf(stderr, "slock: crypt: %s\n", strerror(errno));
+				retval = pam_start(pam_service, hash, &pamc, &pamh);
+				color = PAM;
+				for (screen = 0; screen < nscreens; screen++) {
+					XSetWindowBackground(dpy, locks[screen]->win, locks[screen]->colors[color]);
+					XClearWindow(dpy, locks[screen]->win);
+					XRaiseWindow(dpy, locks[screen]->win);
+				}
+				XSync(dpy, False);
+
+				if (retval == PAM_SUCCESS)
+					retval = pam_authenticate(pamh, 0);
+				if (retval == PAM_SUCCESS)
+					retval = pam_acct_mgmt(pamh, 0);
+
+				running = 1;
+				if (retval == PAM_SUCCESS)
+					running = 0;
 				else
-					running = !!strcmp(inputhash, hash);
+					fprintf(stderr, "slock: %s\n", pam_strerror(pamh, retval));
+				pam_end(pamh, retval);
 				if (running) {
 					XBell(dpy, 100);
 					failure = 1;
@@ -357,10 +407,9 @@ main(int argc, char **argv) {
 	dontkillme();
 #endif
 
+	/* the contents of hash are used to transport the current user name */
 	hash = gethash();
 	errno = 0;
-	if (!crypt("", hash))
-		die("slock: crypt: %s\n", strerror(errno));
 
 	if (!(dpy = XOpenDisplay(NULL)))
 		die("slock: cannot open display\n");
-- 
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