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 <[email protected]>
---
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;
}
--
2.20.1
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 <[email protected]>
> ---
> 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 ?
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 <[email protected]>
> > ---
> > 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?
--
Lukasz Pawelczyk
Samsung R&D Institute Poland
Samsung Electronics
On Wed, 2019-05-08 at 08:41 -0700, Eric Dumazet wrote:
>
> 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 <[email protected]>
> > > > ---
> > > > 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 ?
I think the get_group_info() I mentioned above would. group_info seems
to always be freed by put_group_info().
--
Lukasz Pawelczyk
Samsung R&D Institute Poland
Samsung Electronics
On 5/8/19 11:56 AM, Lukasz Pawelczyk wrote:
> On Wed, 2019-05-08 at 08:41 -0700, Eric Dumazet wrote:
>>
>> 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 <[email protected]>
>>>>> ---
>>>>> 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 ?
>
> I think the get_group_info() I mentioned above would. group_info seems
> to always be freed by put_group_info().
The data can be freed _before_ get_group_info() is attempted.
get_group_info() would do a use-after-free
You would need something like RCU protection over this stuff,
this is not really only a netfilter change.
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 <[email protected]>
>>> ---
>>> 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 ?
On Wed, 2019-05-08 at 09:53 -0700, Eric Dumazet wrote:
>
> On 5/8/19 11:56 AM, Lukasz Pawelczyk wrote:
> > On Wed, 2019-05-08 at 08:41 -0700, Eric Dumazet wrote:
> > > 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 <[email protected]>
> > > > > > ---
> > > > > > 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 ?
> >
> > I think the get_group_info() I mentioned above would. group_info
> > seems
> > to always be freed by put_group_info().
>
> The data can be freed _before_ get_group_info() is attempted.
>
> get_group_info() would do a use-after-free
>
> You would need something like RCU protection over this stuff,
> this is not really only a netfilter change.
>
sk_socket keeps reference to f_cred. f_cred keeps reference to
group_info. As long as f_cred is alive and it doesn't seem to be the
issue in the owner_mt() function, group_info should be alive as well as
far as I can see. Its refcount will go down only when f_cred is freed
(put_cred_rcu()).
If there is something I'm missing please correct me.
--
Lukasz Pawelczyk
Samsung R&D Institute Poland
Samsung Electronics
On Thursday 2019-05-09 12:47, Lukasz Pawelczyk wrote:
>> > > > > > 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,
In keeping with the naming, this should be something like
XT_OWNER_SUPPL_GROUPS.
On 5/9/19 6:47 AM, Lukasz Pawelczyk wrote:
> On Wed, 2019-05-08 at 09:53 -0700, Eric Dumazet wrote:
>>
>> On 5/8/19 11:56 AM, Lukasz Pawelczyk wrote:
>>> On Wed, 2019-05-08 at 08:41 -0700, Eric Dumazet wrote:
>>>> 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 <[email protected]>
>>>>>>> ---
>>>>>>> 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 ?
>>>
>>> I think the get_group_info() I mentioned above would. group_info
>>> seems
>>> to always be freed by put_group_info().
>>
>> The data can be freed _before_ get_group_info() is attempted.
>>
>> get_group_info() would do a use-after-free
>>
>> You would need something like RCU protection over this stuff,
>> this is not really only a netfilter change.
>>
>
> sk_socket keeps reference to f_cred. f_cred keeps reference to
> group_info. As long as f_cred is alive and it doesn't seem to be the
> issue in the owner_mt() function, group_info should be alive as well as
> far as I can see. Its refcount will go down only when f_cred is freed
> (put_cred_rcu()).
>
> If there is something I'm missing please correct me.
The problem is that you can´t clearly explain why the code is safe :/
Why would get_group_info() be needed then ?
You need to explain this in the changelog, so that future bug hunters do not have
to guess.
Note to netfilter maintainers :
owner_mt() reads sk->sk_socket multiple times, this looks racy to me.
(sock_orphan() could be done in the middle from another cpu)
diff --git a/net/netfilter/xt_owner.c b/net/netfilter/xt_owner.c
index 46686fb73784bf71c79282e87e3f01f2c0411f5c..6adfb992bfe1765c57430b4bb98212786086d379 100644
--- a/net/netfilter/xt_owner.c
+++ b/net/netfilter/xt_owner.c
@@ -66,8 +66,10 @@ owner_mt(const struct sk_buff *skb, struct xt_action_param *par)
const struct file *filp;
struct sock *sk = skb_to_full_sk(skb);
struct net *net = xt_net(par);
+ struct socket *sock;
- if (!sk || !sk->sk_socket || !net_eq(net, sock_net(sk)))
+ sock = sk ? READ_ONCE(sk->sk_socket) : NULL;
+ if (!sock || !net_eq(net, sock_net(sk)))
return (info->match ^ info->invert) == 0;
else if (info->match & info->invert & XT_OWNER_SOCKET)
/*
@@ -76,7 +78,7 @@ owner_mt(const struct sk_buff *skb, struct xt_action_param *par)
*/
return false;
- filp = sk->sk_socket->file;
+ filp = sock->file;
if (filp == NULL)
return ((info->match ^ info->invert) &
(XT_OWNER_UID | XT_OWNER_GID)) == 0;
On Thu, 2019-05-09 at 04:57 -0700, Eric Dumazet wrote:
> sk_socket keeps reference to f_cred. f_cred keeps reference to
> > group_info. As long as f_cred is alive and it doesn't seem to be
> > the
> > issue in the owner_mt() function, group_info should be alive as
> > well as
> > far as I can see. Its refcount will go down only when f_cred is
> > freed
> > (put_cred_rcu()).
> >
> > If there is something I'm missing please correct me.
>
> The problem is that you can´t clearly explain why the code is safe :/
>
> Why would get_group_info() be needed then ?
Originally I though it wouldn't, that's why I did not include it in the
patch. Your question made me doubt that for a second. I also got
confused a little because the group_info code looked completely
different a while back, it got reworked and simplified.
>
> You need to explain this in the changelog, so that future bug hunters
> do not have
> to guess.
Ok, I will.
--
Lukasz Pawelczyk
Samsung R&D Institute Poland
Samsung Electronics