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

From: Stephen Hemminger <[email-masked]>
Date: Sat, 16 Mar 2024 08:07:02 -0700

On Sat, 16 Mar 2024 10:06:44 +0100
Max Gautier <[email-masked]> wrote:

> 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";

Make this an array.
const char *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");

Missing signed-off-by