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SubjectRe: [PATCH v2] netfilter: xt_owner: Add supplementary groups option
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On 5/8/19 11:25 AM, Lukasz Pawelczyk wrote:
> On Wed, 2019-05-08 at 07:58 -0700, Eric Dumazet wrote:
>>
>> On 5/8/19 10:12 AM, Lukasz Pawelczyk wrote:
>>> The XT_SUPPL_GROUPS flag causes GIDs specified with XT_OWNER_GID to
>>> be also checked in the supplementary groups of a process.
>>>
>>> Signed-off-by: Lukasz Pawelczyk <l.pawelczyk@samsung.com>
>>> ---
>>> include/uapi/linux/netfilter/xt_owner.h | 1 +
>>> net/netfilter/xt_owner.c | 23 ++++++++++++++++++++-
>>> --
>>> 2 files changed, 21 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/include/uapi/linux/netfilter/xt_owner.h
>>> b/include/uapi/linux/netfilter/xt_owner.h
>>> index fa3ad84957d5..d646f0dc3466 100644
>>> --- a/include/uapi/linux/netfilter/xt_owner.h
>>> +++ b/include/uapi/linux/netfilter/xt_owner.h
>>> @@ -8,6 +8,7 @@ enum {
>>> XT_OWNER_UID = 1 << 0,
>>> XT_OWNER_GID = 1 << 1,
>>> XT_OWNER_SOCKET = 1 << 2,
>>> + XT_SUPPL_GROUPS = 1 << 3,
>>> };
>>>
>>> struct xt_owner_match_info {
>>> diff --git a/net/netfilter/xt_owner.c b/net/netfilter/xt_owner.c
>>> index 46686fb73784..283a1fb5cc52 100644
>>> --- a/net/netfilter/xt_owner.c
>>> +++ b/net/netfilter/xt_owner.c
>>> @@ -91,11 +91,28 @@ owner_mt(const struct sk_buff *skb, struct
>>> xt_action_param *par)
>>> }
>>>
>>> if (info->match & XT_OWNER_GID) {
>>> + unsigned int i, match = false;
>>> kgid_t gid_min = make_kgid(net->user_ns, info-
>>>> gid_min);
>>> kgid_t gid_max = make_kgid(net->user_ns, info-
>>>> gid_max);
>>> - if ((gid_gte(filp->f_cred->fsgid, gid_min) &&
>>> - gid_lte(filp->f_cred->fsgid, gid_max)) ^
>>> - !(info->invert & XT_OWNER_GID))
>>> + struct group_info *gi = filp->f_cred->group_info;
>>> +
>>> + if (gid_gte(filp->f_cred->fsgid, gid_min) &&
>>> + gid_lte(filp->f_cred->fsgid, gid_max))
>>> + match = true;
>>> +
>>> + if (!match && (info->match & XT_SUPPL_GROUPS) && gi) {
>>> + for (i = 0; i < gi->ngroups; ++i) {
>>> + kgid_t group = gi->gid[i];
>>> +
>>> + if (gid_gte(group, gid_min) &&
>>> + gid_lte(group, gid_max)) {
>>> + match = true;
>>> + break;
>>> + }
>>> + }
>>> + }
>>> +
>>> + if (match ^ !(info->invert & XT_OWNER_GID))
>>> return false;
>>> }
>>>
>>>
>>
>> How can this be safe on SMP ?
>>
>
> From what I see after the group_info rework some time ago this struct
> is never modified. It's replaced. Would get_group_info/put_group_info
> around the code be enough?

What prevents the data to be freed right after you fetch filp->f_cred->group_info ?


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