Описание
In the Linux kernel, the following vulnerability has been resolved: inet: frags: drop fraglist conntrack references Jakub added a warning in nf_conntrack_cleanup_net_list() to make debugging leaked skbs/conntrack references more obvious. syzbot reports this as triggering, and I can also reproduce this via ip_defrag.sh selftest: conntrack cleanup blocked for 60s WARNING: net/netfilter/nf_conntrack_core.c:2512 [..] conntrack clenups gets stuck because there are skbs with still hold nf_conn references via their frag_list. net.core.skb_defer_max=0 makes the hang disappear. Eric Dumazet points out that skb_release_head_state() doesn't follow the fraglist. ip_defrag.sh can only reproduce this problem since commit 6471658dc66c ("udp: use skb_attempt_defer_free()"), but AFAICS this problem could happen with TCP as well if pmtu discovery is off. The relevant problem path for udp is:
- netns emits fragmented packets
- nf_defrag_v6_hook reassembles them (in output hook)
- reassembled skb is tracked (skb owns nf_conn reference)
- ip6_output refragments
- refragmented packets also own nf_conn reference (ip6_fragment calls ip6_copy_metadata())
- on input path, nf_defrag_v6_hook skips defragmentation: the fragments already have skb->nf_conn attached
- skbs are reassembled via ipv6_frag_rcv()
- skb_consume_udp -> skb_attempt_defer_free() -> skb ends up
in pcpu freelist, but still has nf_conn reference.
Possible solutions:
1 let defrag engine drop nf_conn entry, OR
2 export kick_defer_list_purge() and call it from the conntrack
netns exit callback, OR
3 add skb_has_frag_list() check to skb_attempt_defer_free()
2 & 3 also solve ip_defrag.sh hang but share same drawback:
Such reassembled skbs, queued to socket, can prevent conntrack module
removal until userspace has consumed the packet. While both tcp and udp
stack do call nf_reset_ct() before placing skb on socket queue, that
function doesn't iterate frag_list skbs.
Therefore drop nf_conn entries when they are placed in defrag queue.
Keep the nf_conn entry of the first (offset 0) skb so that reassembled
skb retains nf_conn entry for sake of TX path.
Note that fixes tag is incorrect; it points to the commit introducing the
'ip_defrag.sh reproducible problem': no need to backport this patch to
every stable kernel.
A flaw was found in the Linux kernel's network connection tracking (conntrack) subsystem. A local user could exploit this by sending specially crafted fragmented network packets. This improper management of connection tracking references can prevent theconntrackmodule from properly releasing resources, leading to a denial of service (DoS) condition.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 10 | kernel | Not affected | ||
| Red Hat Enterprise Linux 6 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel-rt | Not affected | ||
| Red Hat Enterprise Linux 8 | kernel | Not affected | ||
| Red Hat Enterprise Linux 8 | kernel-rt | Not affected | ||
| Red Hat Enterprise Linux 9 | kernel | Not affected | ||
| Red Hat Enterprise Linux 9 | kernel-rt | Not affected |
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Дополнительная информация
Статус:
EPSS
6.1 Medium
CVSS3
Связанные уязвимости
In the Linux kernel, the following vulnerability has been resolved: inet: frags: drop fraglist conntrack references Jakub added a warning in nf_conntrack_cleanup_net_list() to make debugging leaked skbs/conntrack references more obvious. syzbot reports this as triggering, and I can also reproduce this via ip_defrag.sh selftest: conntrack cleanup blocked for 60s WARNING: net/netfilter/nf_conntrack_core.c:2512 [..] conntrack clenups gets stuck because there are skbs with still hold nf_conn references via their frag_list. net.core.skb_defer_max=0 makes the hang disappear. Eric Dumazet points out that skb_release_head_state() doesn't follow the fraglist. ip_defrag.sh can only reproduce this problem since commit 6471658dc66c ("udp: use skb_attempt_defer_free()"), but AFAICS this problem could happen with TCP as well if pmtu discovery is off. The relevant problem path for udp is: 1. netns emits fragmented packets 2. nf_defrag_v6_hook reassembles them (in output hook) 3. reassembled skb is...
In the Linux kernel, the following vulnerability has been resolved: inet: frags: drop fraglist conntrack references Jakub added a warning in nf_conntrack_cleanup_net_list() to make debugging leaked skbs/conntrack references more obvious. syzbot reports this as triggering, and I can also reproduce this via ip_defrag.sh selftest: conntrack cleanup blocked for 60s WARNING: net/netfilter/nf_conntrack_core.c:2512 [..] conntrack clenups gets stuck because there are skbs with still hold nf_conn references via their frag_list. net.core.skb_defer_max=0 makes the hang disappear. Eric Dumazet points out that skb_release_head_state() doesn't follow the fraglist. ip_defrag.sh can only reproduce this problem since commit 6471658dc66c ("udp: use skb_attempt_defer_free()"), but AFAICS this problem could happen with TCP as well if pmtu discovery is off. The relevant problem path for udp is: 1. netns emits fragmented packets 2. nf_defrag_v6_hook reassembles them (in output hook) 3. reasse
In the Linux kernel, the following vulnerability has been resolved: i ...
In the Linux kernel, the following vulnerability has been resolved: inet: frags: drop fraglist conntrack references Jakub added a warning in nf_conntrack_cleanup_net_list() to make debugging leaked skbs/conntrack references more obvious. syzbot reports this as triggering, and I can also reproduce this via ip_defrag.sh selftest: conntrack cleanup blocked for 60s WARNING: net/netfilter/nf_conntrack_core.c:2512 [..] conntrack clenups gets stuck because there are skbs with still hold nf_conn references via their frag_list. net.core.skb_defer_max=0 makes the hang disappear. Eric Dumazet points out that skb_release_head_state() doesn't follow the fraglist. ip_defrag.sh can only reproduce this problem since commit 6471658dc66c ("udp: use skb_attempt_defer_free()"), but AFAICS this problem could happen with TCP as well if pmtu discovery is off. The relevant problem path for udp is: 1. netns emits fragmented packets 2. nf_defrag_v6_hook reassembles them (in output hook) 3. rea...
EPSS
6.1 Medium
CVSS3