* [iptables PATCH v2] iptables: accept lock file name at runtime
@ 2020-07-15 6:51 Giuseppe Scrivano
2020-07-16 21:55 ` Phil Sutter
0 siblings, 1 reply; 3+ messages in thread
From: Giuseppe Scrivano @ 2020-07-15 6:51 UTC (permalink / raw)
To: netfilter-devel; +Cc: gscrivan, Phil Sutter, Florian Westphal
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.
$ 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(-)
diff --git a/iptables/xshared.c b/iptables/xshared.c
index c1d1371a..caf1dfcc 100644
--- a/iptables/xshared.c
+++ b/iptables/xshared.c
@@ -249,12 +249,17 @@ void xs_init_match(struct xtables_match *match)
static int xtables_lock(int wait, struct timeval *wait_interval)
{
struct timeval time_left, wait_time;
+ const char *lock_file;
int fd, i = 0;
time_left.tv_sec = wait;
time_left.tv_usec = 0;
- fd = open(XT_LOCK_NAME, O_CREAT, 0600);
+ lock_file = getenv("XTABLES_LOCKFILE");
+ if (lock_file == NULL || lock_file[0] == '\0')
+ lock_file = XT_LOCK_NAME;
+
+ fd = open(lock_file, O_CREAT, 0600);
if (fd < 0) {
fprintf(stderr, "Fatal: can't open lock file %s: %s\n",
XT_LOCK_NAME, strerror(errno));
--
2.26.2
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [iptables PATCH v2] iptables: accept lock file name at runtime
2020-07-15 6:51 [iptables PATCH v2] iptables: accept lock file name at runtime Giuseppe Scrivano
@ 2020-07-16 21:55 ` Phil Sutter
2020-07-17 8:18 ` Giuseppe Scrivano
0 siblings, 1 reply; 3+ messages in thread
From: Phil Sutter @ 2020-07-16 21:55 UTC (permalink / raw)
To: Giuseppe Scrivano; +Cc: netfilter-devel, Florian Westphal
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.
> $ 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. :)
Cheers, Phil
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [iptables PATCH v2] iptables: accept lock file name at runtime
2020-07-16 21:55 ` Phil Sutter
@ 2020-07-17 8:18 ` Giuseppe Scrivano
0 siblings, 0 replies; 3+ messages in thread
From: Giuseppe Scrivano @ 2020-07-17 8:18 UTC (permalink / raw)
To: Phil Sutter; +Cc: netfilter-devel, Florian Westphal
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
^ permalink raw reply [flat|nested] 3+ messages in thread
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