netdev - [PATCH iproute2-next] arpd: create /var/lib/arpd on first use

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Date: Sat, 16 Mar 2024 10:06:44 +0100
From: Max Gautier <mg@....gautier.name>
To: netdev@...r.kernel.org
Cc: Max Gautier <mg@....gautier.name>
Subject: [PATCH iproute2-next] arpd: create /var/lib/arpd on first use

The motivation is to build distributions packages without /var to go
towards stateless systems, see link below (TL;DR: provisionning anything
outside of /usr on boot).

We only try do create the database directory when it's in the default
location, and assume its parent (/var/lib in the usual case) exists.

Links: https://0pointer.net/blog/projects/stateless.html
---
Instead of modifying the default location, I opted to create it at
runtime, but only for the default location and assuming that /var/lib
exists. My thinking is that not changing defaults is somewhat better,
plus using /var/tmp directly might cause security concerns (I don't know
that it does, but at least someone could create a db file which the root
user would then open by default. Not sure what that could cause, so I'd
rather avoid it).

 Makefile    |  2 +-
 misc/arpd.c | 12 +++++++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 8024d45e..2b2c3dec 100644
--- a/Makefile
+++ b/Makefile
@@ -42,6 +42,7 @@ DEFINES+=-DCONF_USR_DIR=\"$(CONF_USR_DIR)\" \
          -DCONF_ETC_DIR=\"$(CONF_ETC_DIR)\" \
          -DNETNS_RUN_DIR=\"$(NETNS_RUN_DIR)\" \
          -DNETNS_ETC_DIR=\"$(NETNS_ETC_DIR)\" \
+         -DARPDDIR=\"$(ARPDDIR)\" \
          -DCONF_COLOR=$(CONF_COLOR)
 
 #options for AX.25
@@ -104,7 +105,6 @@ config.mk:
 install: all
 	install -m 0755 -d $(DESTDIR)$(SBINDIR)
 	install -m 0755 -d $(DESTDIR)$(CONF_USR_DIR)
-	install -m 0755 -d $(DESTDIR)$(ARPDDIR)
 	install -m 0755 -d $(DESTDIR)$(HDRDIR)
 	@for i in $(SUBDIRS);  do $(MAKE) -C $$i install; done
 	install -m 0644 $(shell find etc/iproute2 -maxdepth 1 -type f) $(DESTDIR)$(CONF_USR_DIR)
diff --git a/misc/arpd.c b/misc/arpd.c
index 1ef837c6..a133226c 100644
--- a/misc/arpd.c
+++ b/misc/arpd.c
@@ -19,6 +19,7 @@
 #include <fcntl.h>
 #include <sys/uio.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 #include <sys/time.h>
 #include <time.h>
 #include <signal.h>
@@ -35,7 +36,8 @@
 #include "rt_names.h"
 
 DB	*dbase;
-char	*dbname = "/var/lib/arpd/arpd.db";
+char const * const	default_dbname = ARPDDIR "/arpd.db";
+char const	*dbname = default_dbname;
 
 int	ifnum;
 int	*ifvec;
@@ -668,6 +670,14 @@ int main(int argc, char **argv)
 		}
 	}
 
+	if (default_dbname == dbname
+			&& mkdir(ARPDDIR, 0755) != 0
+			&& errno != EEXIST
+			) {
+		perror("create_db_dir");
+		exit(-1);
+	}
+
 	dbase = dbopen(dbname, O_CREAT|O_RDWR, 0644, DB_HASH, NULL);
 	if (dbase == NULL) {
 		perror("db_open");
-- 
2.44.0