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

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Message-ID: <04AF6DE2-606E-4CC5-AAC3-CC95CF4896E5@max.gautier.name>
Date: Sun, 17 Mar 2024 01:14:03 +0100
From: Max Gautier <mg@....gautier.name>
To: Jay Vosburgh <jay.vosburgh@...onical.com>,
 Stephen Hemminger <stephen@...workplumber.org>
CC: netdev@...r.kernel.org
Subject: Re: [PATCH iproute2-next] arpd: create /var/lib/arpd on first use

Le 16 mars 2024 20:56:37 GMT+01:00, Jay Vosburgh <jay.vosburgh@...onical.com> a écrit :
>Stephen Hemminger <stephen@...workplumber.org> wrote:
>
>>On Sat, 16 Mar 2024 10:06:44 +0100
>>Max Gautier <mg@....gautier.name> 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).

Yeah, does not compile otherwise, that was my guess as well.

>
>>> +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

I did consider that, the reasoning was mostly something like "if you specify a custom location, you're on your own".
But a string compare is probably best, it preserve the observable behavior of arpd and is overall less surprising. 

I'll send a v2 shortly.

>
>>>  	dbase = dbopen(dbname, O_CREAT|O_RDWR, 0644, DB_HASH, NULL);
>>>  	if (dbase == NULL) {
>>>  		perror("db_open");
>>
>>Missing signed-off-by
>>
>
>---
>	-Jay Vosburgh, jay.vosburgh@...onical.com