PT-2026-121945
CVE-2026-98968
·
Published
2026-10-23
·
Updated
2026-10-23
Description by
Score
N/A
Not availableNo severity ratings or metrics are available. When they are, we'll update the corresponding info on the page.
In the Linux kernel, the following vulnerability has been resolved:
amt: send the relay's General Query directly from the receive path
An skb queued in a qdisc can outlive the tunnel it references
through a raw pointer in skb->cb. For example, with igmp qrv set
to 1 on the relay a tunnel lives for 135s, so a netem delay of
180s on the amt device outlives it; when the tunnel expires and is
freed, the subsequent dequeue triggers a use-after-free in
amt dev xmit().
BUG: KASAN: slab-use-after-free in amt dev xmit+0x2763/0x2e20
Call Trace:
amt dev xmit+0x2763/0x2e20 [drivers/net/amt.c:1262]
dev hard start xmit+0x22f/0x620
sch direct xmit+0x12e/0xac0
netem dequeue+0x333/0xc50
net tx action+0x35c/0xa60
amt send igmp gq() and amt send mld gq() are only called from
amt request handler(), inside the rcu read lock bh() section of
amt rcv(). amt request handler() already has the tunnel the query is
for: it found or created it inside that section. Queuing the query with
dev queue xmit() only leads back into amt dev xmit(), which strips the
Ethernet header and calls amt send membership query() for that tunnel.
Make that call directly from the two senders instead, the same way
amt send advertisement() transmits from the receive path. The query
never waits in a qdisc, the tunnel is only dereferenced inside the
RCU section that found or created it, and nothing is stored in
skb->cb, so no lookup or refcount is needed. Remove the query branch
of amt dev xmit(), amt skb cb() and struct amt skb cb, which have no
users left.
Behaviour changes:
- The relay's own General Queries no longer pass through the amt device's egress path: its qdisc, tc egress (clsact/tcx), the netfilter egress hook and packet taps. They are still visible as UDP on the underlay.
- A query that is sent successfully is no longer counted as tx dropped. The old query branch left through the unlock label, which counted every sent query as dropped.
- A query that reaches amt dev xmit() on a relay from elsewhere, such as a userspace querier, is now dropped at the IGMP/MLD type switch. Before, it trusted whatever skb->cb held, and a NULL tunnel hit the WARN ON(1).
Found an issue in the description? Have something to add? Feel free to write us 👾