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

From: Jay Vosburgh <[email-masked]>
Date: Sat, 16 Mar 2024 12:56:37 -0700

Stephen Hemminger <[email-masked]> wrote:

>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";

	I suspect this should be

const char default_dbname[] = ARPDDIR "/arpd.db";

	i.e., no "*" before "default_dbname", to match the type of
dbname (below).

>> +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);
>> +	}
>> +

	Should this be a string comparison?  I don't think the pointer
comparison "default_dbname == dbname" will do what you expect if a user
specifies "-b" with the default value of ARPDIR "/arpd.db" as its
argument (i.e., the pointers won't match, but the actual text is the
same).

	-J

>>  	dbase = dbopen(dbname, O_CREAT|O_RDWR, 0644, DB_HASH, NULL);
>>  	if (dbase == NULL) {
>>  		perror("db_open");
>
>Missing signed-off-by
>

---
	-Jay Vosburgh, [email-masked]