Re: [iptables PATCH v2] iptables: accept lock file name at runtime

[Giuseppe Scrivano <gscrivan@redhat.com>]

Hi Phil,

thanks for the review.

Phil Sutter <phil@nwl.cc> writes:

> Hi,
>
> On Wed, Jul 15, 2020 at 08:51:52AM +0200, Giuseppe Scrivano wrote:
>> allow users to override at runtime the lock file to use through the
>> XTABLES_LOCKFILE environment variable.
>> 
>> It allows using iptables from a network namespace owned by an user
>> that has no write access to XT_LOCK_NAME (by default under /run), and
>> without setting up a new mount namespace.
>
> This sentence appears overly complicated to me. Isn't the problem just
> that XT_LOCK_NAME may not be writeable? That "user that has no write
> access" is typically root anyway as iptables doesn't support being
> called by non-privileged UIDs.

I'll rephrase it but it is really about the user not having access to the
lock file.

Without involving user namespaces, a simple reproducer for the issue can be:

$ caps="cap_net_admin,cap_net_raw,cap_setpcap,cap_setuid,cap_setgid"
$ capsh --caps="$caps"+eip  --keep=1 --gid=1000 --uid=1000  \
        --addamb="$caps" \
        -- -c "iptables -F ..."

iptables seems to work fine even if the user is not running as root, as
long as enough capabilities are granted.


>> $ XTABLES_LOCKFILE=/tmp/xtables unshare -rn iptables ...
>> 
>> Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
>> ---
>>  iptables/xshared.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> Could you please update the man page as well? Unless you clarify why
> this should be a hidden feature, of course. :)

sure, I'll send a v3 shortly.

Giuseppe