* [PATCH nf] netfilter: nft_set_rbtree: skip transaction elements during GC
@ 2026-09-21 2:08 bestswngs
2026-09-21 12:08 ` Pablo Neira Ayuso
2026-09-21 20:48 ` Pablo Neira Ayuso
0 siblings, 2 replies; 4+ messages in thread
From: bestswngs @ 2026-09-21 2:08 UTC (permalink / raw)
To: pablo, fw, netfilter-devel, coreteam
Cc: phil, xmei5, Weiming Shi, co+ee5e50ef2670e5f4
From: Weiming Shi <bestswngs@gmail.com>
Since nft_set_commit_update() runs set commit callbacks before processing
NEWSETELEM transactions, nft_rbtree_gc_scan() can observe elements added by
the transaction being committed.
The scan records an interval end in rbe_end without checking the element's
transaction state. A later, unrelated expired start then moves both
elements to the expired list. The synchronous GC queue can free the new end
element before the transaction subsequently activates it, causing a
use-after-free.
Only consider elements that are fully active in both generations. This
keeps transaction-state elements out of the GC scan and preserves interval
pairing across skipped elements.
KASAN reports:
BUG: KASAN: slab-use-after-free in nft_setelem_activate
nft_setelem_activate net/netfilter/nf_tables_api.c:7047
nf_tables_commit net/netfilter/nf_tables_api.c:11137
Allocated by task 130:
nft_set_elem_init net/netfilter/nf_tables_api.c:6794
nft_add_set_elem net/netfilter/nf_tables_api.c:7523
Freed by task 130:
nft_trans_gc_trans_free net/netfilter/nf_tables_api.c:10506
rcu_core kernel/rcu/tree.c:2919
Fixes: 1e3b9e1c77fe ("netfilter: nf_tables: call set ops .commit when building new ruleset blob")
Reported-by: <co+ee5e50ef2670e5f4@bugs.sh>
Assisted-by: LLM
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
net/netfilter/nft_set_rbtree.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
index 9894832281c4b..12431b55752fb 100644
--- a/net/netfilter/nft_set_rbtree.c
+++ b/net/netfilter/nft_set_rbtree.c
@@ -900,6 +900,8 @@ static void nft_rbtree_gc_scan(struct nft_set *set)
next = rb_next(node);
rbe = rb_entry(node, struct nft_rbtree_elem, node);
+ if (!nft_set_elem_active(&rbe->ext, NFT_GENMASK_ANY))
+ continue;
/* elements are reversed in the rbtree for historical reasons,
* from highest to lowest value, that is why end element is
--
2.55.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH nf] netfilter: nft_set_rbtree: skip transaction elements during GC
2026-09-21 2:08 [PATCH nf] netfilter: nft_set_rbtree: skip transaction elements during GC bestswngs
@ 2026-09-21 12:08 ` Pablo Neira Ayuso
2026-09-21 12:29 ` Pablo Neira Ayuso
2026-09-21 20:48 ` Pablo Neira Ayuso
1 sibling, 1 reply; 4+ messages in thread
From: Pablo Neira Ayuso @ 2026-09-21 12:08 UTC (permalink / raw)
To: bestswngs; +Cc: fw, netfilter-devel, coreteam, phil, xmei5, co+ee5e50ef2670e5f4
On Mon, Sep 21, 2026 at 10:08:22AM +0800, bestswngs@gmail.com wrote:
> From: Weiming Shi <bestswngs@gmail.com>
>
> Since nft_set_commit_update() runs set commit callbacks before processing
> NEWSETELEM transactions, nft_rbtree_gc_scan() can observe elements added by
> the transaction being committed.
>
> The scan records an interval end in rbe_end without checking the element's
> transaction state. A later, unrelated expired start then moves both
> elements to the expired list. The synchronous GC queue can free the new end
> element before the transaction subsequently activates it, causing a
> use-after-free.
>
> Only consider elements that are fully active in both generations. This
> keeps transaction-state elements out of the GC scan and preserves interval
> pairing across skipped elements.
>
> KASAN reports:
>
> BUG: KASAN: slab-use-after-free in nft_setelem_activate
> nft_setelem_activate net/netfilter/nf_tables_api.c:7047
> nf_tables_commit net/netfilter/nf_tables_api.c:11137
>
> Allocated by task 130:
> nft_set_elem_init net/netfilter/nf_tables_api.c:6794
> nft_add_set_elem net/netfilter/nf_tables_api.c:7523
>
> Freed by task 130:
> nft_trans_gc_trans_free net/netfilter/nf_tables_api.c:10506
> rcu_core kernel/rcu/tree.c:2919
>
> Fixes: 1e3b9e1c77fe ("netfilter: nf_tables: call set ops .commit when building new ruleset blob")
> Reported-by: <co+ee5e50ef2670e5f4@bugs.sh>
> Assisted-by: LLM
> Signed-off-by: Weiming Shi <bestswngs@gmail.com>
> ---
> net/netfilter/nft_set_rbtree.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
> index 9894832281c4b..12431b55752fb 100644
> --- a/net/netfilter/nft_set_rbtree.c
> +++ b/net/netfilter/nft_set_rbtree.c
> @@ -900,6 +900,8 @@ static void nft_rbtree_gc_scan(struct nft_set *set)
> next = rb_next(node);
>
> rbe = rb_entry(node, struct nft_rbtree_elem, node);
> + if (!nft_set_elem_active(&rbe->ext, NFT_GENMASK_ANY))
> + continue;
>
> /* elements are reversed in the rbtree for historical reasons,
> * from highest to lowest value, that is why end element is
Maybe simply set rbe_end to NULL when rbe is found and is not
expired?
diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
index 9894832281c4..a9f2ae3c91cf 100644
--- a/net/netfilter/nft_set_rbtree.c
+++ b/net/netfilter/nft_set_rbtree.c
@@ -909,8 +909,10 @@ static void nft_rbtree_gc_scan(struct nft_set *set)
rbe_end = rbe;
continue;
}
- if (!__nft_set_elem_expired(&rbe->ext, tstamp))
+ if (!__nft_set_elem_expired(&rbe->ext, tstamp)) {
+ rbe_end = NULL;
continue;
+ }
/* end element needs to be removed first, it has
* no timeout extension.
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH nf] netfilter: nft_set_rbtree: skip transaction elements during GC
2026-09-21 12:08 ` Pablo Neira Ayuso
@ 2026-09-21 12:29 ` Pablo Neira Ayuso
0 siblings, 0 replies; 4+ messages in thread
From: Pablo Neira Ayuso @ 2026-09-21 12:29 UTC (permalink / raw)
To: bestswngs; +Cc: fw, netfilter-devel, coreteam, phil, xmei5, co+ee5e50ef2670e5f4
On Mon, Sep 21, 2026 at 02:08:40PM +0200, Pablo Neira Ayuso wrote:
> On Mon, Sep 21, 2026 at 10:08:22AM +0800, bestswngs@gmail.com wrote:
> > From: Weiming Shi <bestswngs@gmail.com>
> >
> > Since nft_set_commit_update() runs set commit callbacks before processing
> > NEWSETELEM transactions, nft_rbtree_gc_scan() can observe elements added by
> > the transaction being committed.
> >
> > The scan records an interval end in rbe_end without checking the element's
> > transaction state. A later, unrelated expired start then moves both
> > elements to the expired list.
> >
> > The synchronous GC queue can free the new end
> > element before the transaction subsequently activates it, causing a
> > use-after-free.
> >
> > Only consider elements that are fully active in both generations. This
> > keeps transaction-state elements out of the GC scan and preserves interval
> > pairing across skipped elements.
> >
> > KASAN reports:
> >
> > BUG: KASAN: slab-use-after-free in nft_setelem_activate
> > nft_setelem_activate net/netfilter/nf_tables_api.c:7047
> > nf_tables_commit net/netfilter/nf_tables_api.c:11137
> >
> > Allocated by task 130:
> > nft_set_elem_init net/netfilter/nf_tables_api.c:6794
> > nft_add_set_elem net/netfilter/nf_tables_api.c:7523
> >
> > Freed by task 130:
> > nft_trans_gc_trans_free net/netfilter/nf_tables_api.c:10506
> > rcu_core kernel/rcu/tree.c:2919
> >
> > Fixes: 1e3b9e1c77fe ("netfilter: nf_tables: call set ops .commit when building new ruleset blob")
> > Reported-by: <co+ee5e50ef2670e5f4@bugs.sh>
> > Assisted-by: LLM
> > Signed-off-by: Weiming Shi <bestswngs@gmail.com>
> > ---
> > net/netfilter/nft_set_rbtree.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
> > index 9894832281c4b..12431b55752fb 100644
> > --- a/net/netfilter/nft_set_rbtree.c
> > +++ b/net/netfilter/nft_set_rbtree.c
> > @@ -900,6 +900,8 @@ static void nft_rbtree_gc_scan(struct nft_set *set)
> > next = rb_next(node);
> >
> > rbe = rb_entry(node, struct nft_rbtree_elem, node);
> > + if (!nft_set_elem_active(&rbe->ext, NFT_GENMASK_ANY))
> > + continue;
> >
> > /* elements are reversed in the rbtree for historical reasons,
> > * from highest to lowest value, that is why end element is
>
> Maybe simply set rbe_end to NULL when rbe is found and is not
> expired?
>
> diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
> index 9894832281c4..a9f2ae3c91cf 100644
> --- a/net/netfilter/nft_set_rbtree.c
> +++ b/net/netfilter/nft_set_rbtree.c
> @@ -909,8 +909,10 @@ static void nft_rbtree_gc_scan(struct nft_set *set)
> rbe_end = rbe;
> continue;
> }
> - if (!__nft_set_elem_expired(&rbe->ext, tstamp))
> + if (!__nft_set_elem_expired(&rbe->ext, tstamp)) {
> + rbe_end = NULL;
> continue;
> + }
>
> /* end element needs to be removed first, it has
> * no timeout extension.
My proposed chunk is not correct, it still allows for the problem to
happen.
Maybe restrict this to:
diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
index 9894832281c4..bc331c6ae339 100644
--- a/net/netfilter/nft_set_rbtree.c
+++ b/net/netfilter/nft_set_rbtree.c
@@ -905,7 +905,8 @@ static void nft_rbtree_gc_scan(struct nft_set *set)
* from highest to lowest value, that is why end element is
* always visited before the start element.
*/
- if (nft_rbtree_interval_end(rbe)) {
+ if (nft_rbtree_interval_end(rbe) &&
+ nft_set_elem_active(&rbe->ext, NFT_GENMASK_ANY)) {
rbe_end = rbe;
continue;
}
for symmetry with:
commit 60c0c230c6f046da536d3df8b39a20b9a9fd6af0
Author: Pablo Neira Ayuso <pablo@netfilter.org>
Date: Wed Feb 7 18:49:51 2024 +0100
netfilter: nft_set_rbtree: skip end interval element from gc
But I suspect this is leaving stale (expired) overlapping intervals in
the set when building it from nft_rbtree_commit(), so the fix still
looks incomplete me.
I want to have a close look and make a test case for this, this is not
well covered by tests.
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH nf] netfilter: nft_set_rbtree: skip transaction elements during GC
2026-09-21 2:08 [PATCH nf] netfilter: nft_set_rbtree: skip transaction elements during GC bestswngs
2026-09-21 12:08 ` Pablo Neira Ayuso
@ 2026-09-21 20:48 ` Pablo Neira Ayuso
1 sibling, 0 replies; 4+ messages in thread
From: Pablo Neira Ayuso @ 2026-09-21 20:48 UTC (permalink / raw)
To: bestswngs; +Cc: fw, netfilter-devel, coreteam, phil, xmei5, co+ee5e50ef2670e5f4
On Mon, Sep 21, 2026 at 10:08:22AM +0800, bestswngs@gmail.com wrote:
> From: Weiming Shi <bestswngs@gmail.com>
>
> Since nft_set_commit_update() runs set commit callbacks before processing
> NEWSETELEM transactions, nft_rbtree_gc_scan() can observe elements added by
> the transaction being committed.
>
> The scan records an interval end in rbe_end without checking the element's
> transaction state. A later, unrelated expired start then moves both
> elements to the expired list. The synchronous GC queue can free the new end
> element before the transaction subsequently activates it, causing a
> use-after-free.
>
> Only consider elements that are fully active in both generations. This
> keeps transaction-state elements out of the GC scan and preserves interval
> pairing across skipped elements.
>
> KASAN reports:
>
> BUG: KASAN: slab-use-after-free in nft_setelem_activate
> nft_setelem_activate net/netfilter/nf_tables_api.c:7047
> nf_tables_commit net/netfilter/nf_tables_api.c:11137
>
> Allocated by task 130:
> nft_set_elem_init net/netfilter/nf_tables_api.c:6794
> nft_add_set_elem net/netfilter/nf_tables_api.c:7523
>
> Freed by task 130:
> nft_trans_gc_trans_free net/netfilter/nf_tables_api.c:10506
> rcu_core kernel/rcu/tree.c:2919
>
> Fixes: 1e3b9e1c77fe ("netfilter: nf_tables: call set ops .commit when building new ruleset blob")
> Reported-by: <co+ee5e50ef2670e5f4@bugs.sh>
> Assisted-by: LLM
> Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Patch is fine. It is not possible to add or delete an expired element,
expired elements should not ever be in a transaction then.
> ---
> net/netfilter/nft_set_rbtree.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
> index 9894832281c4b..12431b55752fb 100644
> --- a/net/netfilter/nft_set_rbtree.c
> +++ b/net/netfilter/nft_set_rbtree.c
> @@ -900,6 +900,8 @@ static void nft_rbtree_gc_scan(struct nft_set *set)
> next = rb_next(node);
>
> rbe = rb_entry(node, struct nft_rbtree_elem, node);
> + if (!nft_set_elem_active(&rbe->ext, NFT_GENMASK_ANY))
> + continue;
>
> /* elements are reversed in the rbtree for historical reasons,
> * from highest to lowest value, that is why end element is
> --
> 2.55.0
>
^ permalink raw reply [flat|nested] 4+ messages in thread
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2026-09-21 2:08 [PATCH nf] netfilter: nft_set_rbtree: skip transaction elements during GC bestswngs
2026-09-21 12:08 ` Pablo Neira Ayuso
2026-09-21 12:29 ` Pablo Neira Ayuso
2026-09-21 20:48 ` Pablo Neira Ayuso
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