From a37db38a47c02ad652a2043e90d3e8994175260f Mon Sep 17 00:00:00 2001
From: Alex Karle <alex@alexkarle.com>
Date: Sun, 25 Apr 2021 23:29:41 -0400
Subject: [PATCH] kiosk: Replace mandoc(1) usage with less(1) on prebuilt files

Here we go again with runtime optimization at the cost of build time!
This patch removes the usage of `mandoc -l` on the contents of the
site and replaces it with straight less(1).

This is done by generating the kiosk-facing content at build time.

The *real* win here is that it allows us to add unveil(2) calls to
the kiosk, hiding all but the exported files from the field of view
of the process!

I was _tempted_ to replace less(1) with just straight printing the
file line by line to stdout... but I thought that was a bit drastic!

It would give us a super tight pledge though... hmm
---
 .gitignore  |  3 ++-
 Makefile    |  4 +++-
 src/kiosk.c | 38 ++++++++++++++++++++------------------
 3 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/.gitignore b/.gitignore
index 859c651..dd8b7c4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,5 +7,6 @@ atom.xml
 # jam-tuesday hits generated by jam-tuesday/stats.sh
 jam-tuesday/greatest-hits
 
-# kiosk binary
+# kiosk binary and files
 bin/kiosk
+kiosk/
diff --git a/Makefile b/Makefile
index 44e71fb..134ae71 100644
--- a/Makefile
+++ b/Makefile
@@ -33,7 +33,7 @@ jam-tuesday/greatest-hits: $(SETS) bin/jam-stats.sh
 	(date; echo; ./bin/jam-stats.sh) > $@
 
 bin/kiosk: src/kiosk.c
-	$(CC) $(CFLAGS) -DMANDIR="\"`pwd`\"" src/kiosk.c -o $@
+	$(CC) $(CFLAGS) -DMANDIR="\"`pwd`/kiosk\"" src/kiosk.c -o $@
 
 $(HTML): bin/genpost.sh
 
@@ -42,3 +42,5 @@ $(HTML): bin/genpost.sh
 	@echo "mandoc $<"
 	$(HIDE)mandoc -Tlint -Werror $<
 	$(HIDE)./bin/genpost.sh	< $< > $@
+	$(HIDE)mkdir -p kiosk
+	$(HIDE)mandoc $< > kiosk/`basename $@ .html`
diff --git a/src/kiosk.c b/src/kiosk.c
index 0077542..cd164b4 100644
--- a/src/kiosk.c
+++ b/src/kiosk.c
@@ -11,11 +11,8 @@ int list(void) {
     struct dirent *dp;
     int n = 0;
     while ((dp = readdir(dirp)) != NULL) {
-        size_t len = strlen(dp->d_name);
-        if (len < 3)
-            continue;
-        if (strcmp(dp->d_name + (len - 2), ".7") == 0) {
-            dp->d_name[len - 2] = '\0'; /* truncate extension */
+        /* ignore hidden files (and, conveniently, . and ..) */
+        if (dp->d_name[0] != '.') {
             printf("%2d: %s(7)\n", ++n, dp->d_name);
         }
     }
@@ -48,17 +45,12 @@ void mandoc(int choice) {
     struct dirent *dp;
     int i = 0;
     while ((dp = readdir(dirp)) != NULL) {
-        size_t len = strlen(dp->d_name);
-        if (len < 3)
-            continue;
-        if (strcmp(dp->d_name + (len - 2), ".7") == 0) {
-            if (++i == choice) {
-                char *cmd_base = "mandoc -l";
-                char cmd[sizeof(cmd_base) + PATH_MAX + 2];
-                sprintf(cmd, "%s %s/%s", cmd_base, MANDIR, dp->d_name);
-                system(cmd);
-                break;
-            }
+        if (dp->d_name[0] != '.' && ++i == choice) {
+            char *cmd_base = "less";
+            char cmd[sizeof(cmd_base) + PATH_MAX + 2];
+            sprintf(cmd, "%s %s/%s", cmd_base, MANDIR, dp->d_name);
+            system(cmd);
+            break;
         }
     }
     closedir(dirp);
@@ -103,10 +95,20 @@ void prompt(int n) {
 
 int main(void) {
 #ifdef __OpenBSD__
-    pledge("stdio rpath proc exec", NULL);
+    /* All unveils for this proc only (not for less) */
+    if (unveil(MANDIR, "r") == -1)
+        err(1, "unveil");
+    if (unveil("/usr/bin/less", "rx") == -1)
+        err(1, "unveil");
+    if (unveil("/dev/tty", "r") == -1)
+        err(1, "unveil");
+    if (unveil("/bin/sh", "rx") == -1) /* for system(3) */
+        err(1, "unveil");
+    /* no more unveil's past here! requires pledge*/
+    if (pledge("stdio rpath proc exec", NULL) == -1)
+        err(1, "pledge");
 #endif
     int n = list();
-    setenv("MANPAGER", "less", 0);
     setenv("LESSSECURE", "1", 1);
     for(;;)
         prompt(n);
--
libgit2 1.1.1