linux-stable.git/include/net, branch v5.15.208 Linux kernel stable tree netfilter: nft_ct: fix use-after-free in timeout object destroy 2026-04-18T08:33:36+00:00 Tuan Do tuan@calif.io 2026-04-03T07:33:17+00:00 c581e5c8f2b59158f62efe61c1a3dc36189081ff commit f8dca15a1b190787bbd03285304b569631160eda upstream. nft_ct_timeout_obj_destroy() frees the timeout object with kfree() immediately after nf_ct_untimeout(), without waiting for an RCU grace period. Concurrent packet processing on other CPUs may still hold RCU-protected references to the timeout object obtained via rcu_dereference() in nf_ct_timeout_data(). Add an rcu_head to struct nf_ct_timeout and use kfree_rcu() to defer freeing until after an RCU grace period, matching the approach already used in nfnetlink_cttimeout.c. KASAN report: BUG: KASAN: slab-use-after-free in nf_conntrack_tcp_packet+0x1381/0x29d0 Read of size 4 at addr ffff8881035fe19c by task exploit/80 Call Trace: nf_conntrack_tcp_packet+0x1381/0x29d0 nf_conntrack_in+0x612/0x8b0 nf_hook_slow+0x70/0x100 __ip_local_out+0x1b2/0x210 tcp_sendmsg_locked+0x722/0x1580 __sys_sendto+0x2d8/0x320 Allocated by task 75: nft_ct_timeout_obj_init+0xf6/0x290 nft_obj_init+0x107/0x1b0 nf_tables_newobj+0x680/0x9c0 nfnetlink_rcv_batch+0xc29/0xe00 Freed by task 26: nft_obj_destroy+0x3f/0xa0 nf_tables_trans_destroy_work+0x51c/0x5c0 process_one_work+0x2c4/0x5a0 Fixes: 7e0b2b57f01d ("netfilter: nft_ct: add ct timeout support") Cc: stable@vger.kernel.org Signed-off-by: Tuan Do <tuan@calif.io> Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit f8dca15a1b190787bbd03285304b569631160eda upstream.

nft_ct_timeout_obj_destroy() frees the timeout object with kfree()
immediately after nf_ct_untimeout(), without waiting for an RCU grace
period. Concurrent packet processing on other CPUs may still hold
RCU-protected references to the timeout object obtained via
rcu_dereference() in nf_ct_timeout_data().

Add an rcu_head to struct nf_ct_timeout and use kfree_rcu() to defer
freeing until after an RCU grace period, matching the approach already
used in nfnetlink_cttimeout.c.

KASAN report:
 BUG: KASAN: slab-use-after-free in nf_conntrack_tcp_packet+0x1381/0x29d0
 Read of size 4 at addr ffff8881035fe19c by task exploit/80

 Call Trace:
  nf_conntrack_tcp_packet+0x1381/0x29d0
  nf_conntrack_in+0x612/0x8b0
  nf_hook_slow+0x70/0x100
  __ip_local_out+0x1b2/0x210
  tcp_sendmsg_locked+0x722/0x1580
  __sys_sendto+0x2d8/0x320

 Allocated by task 75:
  nft_ct_timeout_obj_init+0xf6/0x290
  nft_obj_init+0x107/0x1b0
  nf_tables_newobj+0x680/0x9c0
  nfnetlink_rcv_batch+0xc29/0xe00

 Freed by task 26:
  nft_obj_destroy+0x3f/0xa0
  nf_tables_trans_destroy_work+0x51c/0x5c0
  process_one_work+0x2c4/0x5a0

Fixes: 7e0b2b57f01d ("netfilter: nft_ct: add ct timeout support")
Cc: stable@vger.kernel.org
Signed-off-by: Tuan Do <tuan@calif.io>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
netlink: allow be16 and be32 types in all uint policy checks 2026-04-18T08:33:25+00:00 Florian Westphal fw@strlen.de 2023-07-18T07:52:29+00:00 72f3c34de5fdcfa2fbd712e2dbb4265889ed38be [ Upstream commit 5fac9b7c16c50c6c7699517f582b56e3743f453a ] __NLA_IS_BEINT_TYPE(tp) isn't useful. NLA_BE16/32 are identical to NLA_U16/32, the only difference is that it tells the netlink validation functions that byteorder conversion might be needed before comparing the value to the policy min/max ones. After this change all policy macros that can be used with UINT types, such as NLA_POLICY_MASK() can also be used with NLA_BE16/32. This will be used to validate nf_tables flag attributes which are in bigendian byte order. Signed-off-by: Florian Westphal <fw@strlen.de> Stable-dep-of: 8f15b5071b45 ("netfilter: ctnetlink: use netlink policy range checks") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 5fac9b7c16c50c6c7699517f582b56e3743f453a ]

__NLA_IS_BEINT_TYPE(tp) isn't useful.  NLA_BE16/32 are identical to
NLA_U16/32, the only difference is that it tells the netlink validation
functions that byteorder conversion might be needed before comparing
the value to the policy min/max ones.

After this change all policy macros that can be used with UINT types,
such as NLA_POLICY_MASK() can also be used with NLA_BE16/32.

This will be used to validate nf_tables flag attributes which
are in bigendian byte order.

Signed-off-by: Florian Westphal <fw@strlen.de>
Stable-dep-of: 8f15b5071b45 ("netfilter: ctnetlink: use netlink policy range checks")
Signed-off-by: Sasha Levin <sashal@kernel.org>
netlink: introduce bigendian integer types 2026-04-18T08:33:25+00:00 Florian Westphal fw@strlen.de 2022-10-31T12:34:07+00:00 cbfac0add2afe8960a09806012313765a2179423 [ Upstream commit ecaf75ffd5f5db320d8b1da0198eef5a5ce64a3f ] Jakub reported that the addition of the "network_byte_order" member in struct nla_policy increases size of 32bit platforms. Instead of scraping the bit from elsewhere Johannes suggested to add explicit NLA_BE types instead, so do this here. NLA_POLICY_MAX_BE() macro is removed again, there is no need for it: NLA_POLICY_MAX(NLA_BE.., ..) will do the right thing. NLA_BE64 can be added later. Fixes: 08724ef69907 ("netlink: introduce NLA_POLICY_MAX_BE") Reported-by: Jakub Kicinski <kuba@kernel.org> Suggested-by: Johannes Berg <johannes@sipsolutions.net> Signed-off-by: Florian Westphal <fw@strlen.de> Link: https://lore.kernel.org/r/20221031123407.9158-1-fw@strlen.de Signed-off-by: Jakub Kicinski <kuba@kernel.org> Stable-dep-of: 8f15b5071b45 ("netfilter: ctnetlink: use netlink policy range checks") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit ecaf75ffd5f5db320d8b1da0198eef5a5ce64a3f ]

Jakub reported that the addition of the "network_byte_order"
member in struct nla_policy increases size of 32bit platforms.

Instead of scraping the bit from elsewhere Johannes suggested
to add explicit NLA_BE types instead, so do this here.

NLA_POLICY_MAX_BE() macro is removed again, there is no need
for it: NLA_POLICY_MAX(NLA_BE.., ..) will do the right thing.

NLA_BE64 can be added later.

Fixes: 08724ef69907 ("netlink: introduce NLA_POLICY_MAX_BE")
Reported-by: Jakub Kicinski <kuba@kernel.org>
Suggested-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/20221031123407.9158-1-fw@strlen.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 8f15b5071b45 ("netfilter: ctnetlink: use netlink policy range checks")
Signed-off-by: Sasha Levin <sashal@kernel.org>
netlink: hide validation union fields from kdoc 2026-04-18T08:33:25+00:00 Jakub Kicinski kuba@kernel.org 2022-10-27T21:21:07+00:00 72eab86197c079ca00a0b3f402d2161a6125e69e [ Upstream commit 7354c9024f2835f6122ed9612e21ab379df050f9 ] Mark the validation fields as private, users shouldn't set them directly and they are too complicated to explain in a more succinct way (there's already a long explanation in the comment above). The strict_start_type field is set directly and has a dedicated comment so move that above the "private" section. Link: https://lore.kernel.org/r/20221027212107.2639255-1-kuba@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org> Stable-dep-of: 8f15b5071b45 ("netfilter: ctnetlink: use netlink policy range checks") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 7354c9024f2835f6122ed9612e21ab379df050f9 ]

Mark the validation fields as private, users shouldn't set
them directly and they are too complicated to explain in
a more succinct way (there's already a long explanation
in the comment above).

The strict_start_type field is set directly and has a dedicated
comment so move that above the "private" section.

Link: https://lore.kernel.org/r/20221027212107.2639255-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 8f15b5071b45 ("netfilter: ctnetlink: use netlink policy range checks")
Signed-off-by: Sasha Levin <sashal@kernel.org>
netlink: introduce NLA_POLICY_MAX_BE 2026-04-18T08:33:25+00:00 Florian Westphal fw@strlen.de 2022-09-05T10:09:36+00:00 dd9df463d732aac40ccb57431847c82b6c2910b8 [ Upstream commit 08724ef69907214ce622344fe4945412e38368f0 ] netlink allows to specify allowed ranges for integer types. Unfortunately, nfnetlink passes integers in big endian, so the existing NLA_POLICY_MAX() cannot be used. At the moment, nfnetlink users, such as nf_tables, need to resort to programmatic checking via helpers such as nft_parse_u32_check(). This is both cumbersome and error prone. This adds NLA_POLICY_MAX_BE which adds range check support for BE16, BE32 and BE64 integers. Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: David S. Miller <davem@davemloft.net> Stable-dep-of: 8f15b5071b45 ("netfilter: ctnetlink: use netlink policy range checks") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 08724ef69907214ce622344fe4945412e38368f0 ]

netlink allows to specify allowed ranges for integer types.
Unfortunately, nfnetlink passes integers in big endian, so the existing
NLA_POLICY_MAX() cannot be used.

At the moment, nfnetlink users, such as nf_tables, need to resort to
programmatic checking via helpers such as nft_parse_u32_check().

This is both cumbersome and error prone.  This adds NLA_POLICY_MAX_BE
which adds range check support for BE16, BE32 and BE64 integers.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 8f15b5071b45 ("netfilter: ctnetlink: use netlink policy range checks")
Signed-off-by: Sasha Levin <sashal@kernel.org>
netfilter: nft_set_pipapo: split gc into unlink and reclaim phase 2026-04-18T08:33:22+00:00 Florian Westphal fw@strlen.de 2026-03-03T15:31:32+00:00 c0f1f85097ac2b6e7d750fe4d05807985cd3fd3a commit 9df95785d3d8302f7c066050117b04cd3c2048c2 upstream. Yiming Qian reports Use-after-free in the pipapo set type: Under a large number of expired elements, commit-time GC can run for a very long time in a non-preemptible context, triggering soft lockup warnings and RCU stall reports (local denial of service). We must split GC in an unlink and a reclaim phase. We cannot queue elements for freeing until pointers have been swapped. Expired elements are still exposed to both the packet path and userspace dumpers via the live copy of the data structure. call_rcu() does not protect us: dump operations or element lookups starting after call_rcu has fired can still observe the free'd element, unless the commit phase has made enough progress to swap the clone and live pointers before any new reader has picked up the old version. This a similar approach as done recently for the rbtree backend in commit 35f83a75529a ("netfilter: nft_set_rbtree: don't gc elements on insert"). Fixes: 3c4287f62044 ("nf_tables: Add set type for arbitrary concatenation of ranges") Reported-by: Yiming Qian <yimingqian591@gmail.com> Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 9df95785d3d8302f7c066050117b04cd3c2048c2 upstream.

Yiming Qian reports Use-after-free in the pipapo set type:
  Under a large number of expired elements, commit-time GC can run for a very
  long time in a non-preemptible context, triggering soft lockup warnings and
  RCU stall reports (local denial of service).

We must split GC in an unlink and a reclaim phase.

We cannot queue elements for freeing until pointers have been swapped.
Expired elements are still exposed to both the packet path and userspace
dumpers via the live copy of the data structure.

call_rcu() does not protect us: dump operations or element lookups starting
after call_rcu has fired can still observe the free'd element, unless the
commit phase has made enough progress to swap the clone and live pointers
before any new reader has picked up the old version.

This a similar approach as done recently for the rbtree backend in commit
35f83a75529a ("netfilter: nft_set_rbtree: don't gc elements on insert").

Fixes: 3c4287f62044 ("nf_tables: Add set type for arbitrary concatenation of ranges")
Reported-by: Yiming Qian <yimingqian591@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
netfilter: nf_tables: de-constify set commit ops function argument 2026-04-18T08:33:22+00:00 Florian Westphal fw@strlen.de 2023-10-13T12:18:14+00:00 d725560f80ad4cf0893fd4b6255d9cecf07a8419 commit 256001672153af5786c6ca148114693d7d76d836 upstream. The set backend using this already has to work around this via ugly cast, don't spread this pattern. Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 256001672153af5786c6ca148114693d7d76d836 upstream.

The set backend using this already has to work around this via ugly
cast, don't spread this pattern.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
udp_tunnel: fix NULL deref caused by udp_sock_create6 when CONFIG_IPV6=n 2026-04-18T08:33:21+00:00 Xiang Mei xmei5@asu.edu 2026-03-17T01:02:41+00:00 66117dbb3dbae82f86735bf727b1d59cc677afa1 [ Upstream commit b3a6df291fecf5f8a308953b65ca72b7fc9e015d ] When CONFIG_IPV6 is disabled, the udp_sock_create6() function returns 0 (success) without actually creating a socket. Callers such as fou_create() then proceed to dereference the uninitialized socket pointer, resulting in a NULL pointer dereference. The captured NULL deref crash: BUG: kernel NULL pointer dereference, address: 0000000000000018 RIP: 0010:fou_nl_add_doit (net/ipv4/fou_core.c:590 net/ipv4/fou_core.c:764) [...] Call Trace: <TASK> genl_family_rcv_msg_doit.constprop.0 (net/netlink/genetlink.c:1114) genl_rcv_msg (net/netlink/genetlink.c:1194 net/netlink/genetlink.c:1209) [...] netlink_rcv_skb (net/netlink/af_netlink.c:2550) genl_rcv (net/netlink/genetlink.c:1219) netlink_unicast (net/netlink/af_netlink.c:1319 net/netlink/af_netlink.c:1344) netlink_sendmsg (net/netlink/af_netlink.c:1894) __sock_sendmsg (net/socket.c:727 (discriminator 1) net/socket.c:742 (discriminator 1)) __sys_sendto (./include/linux/file.h:62 (discriminator 1) ./include/linux/file.h:83 (discriminator 1) net/socket.c:2183 (discriminator 1)) __x64_sys_sendto (net/socket.c:2213 (discriminator 1) net/socket.c:2209 (discriminator 1) net/socket.c:2209 (discriminator 1)) do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1)) entry_SYSCALL_64_after_hwframe (net/arch/x86/entry/entry_64.S:130) This patch makes udp_sock_create6 return -EPFNOSUPPORT instead, so callers correctly take their error paths. There is only one caller of the vulnerable function and only privileged users can trigger it. Fixes: fd384412e199b ("udp_tunnel: Seperate ipv6 functions into its own file.") Reported-by: Weiming Shi <bestswngs@gmail.com> Signed-off-by: Xiang Mei <xmei5@asu.edu> Link: https://patch.msgid.link/20260317010241.1893893-1-xmei5@asu.edu Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit b3a6df291fecf5f8a308953b65ca72b7fc9e015d ]

When CONFIG_IPV6 is disabled, the udp_sock_create6() function returns 0
(success) without actually creating a socket. Callers such as
fou_create() then proceed to dereference the uninitialized socket
pointer, resulting in a NULL pointer dereference.

The captured NULL deref crash:
  BUG: kernel NULL pointer dereference, address: 0000000000000018
  RIP: 0010:fou_nl_add_doit (net/ipv4/fou_core.c:590 net/ipv4/fou_core.c:764)
  [...]
  Call Trace:
    <TASK>
    genl_family_rcv_msg_doit.constprop.0 (net/netlink/genetlink.c:1114)
    genl_rcv_msg (net/netlink/genetlink.c:1194 net/netlink/genetlink.c:1209)
    [...]
    netlink_rcv_skb (net/netlink/af_netlink.c:2550)
    genl_rcv (net/netlink/genetlink.c:1219)
    netlink_unicast (net/netlink/af_netlink.c:1319 net/netlink/af_netlink.c:1344)
    netlink_sendmsg (net/netlink/af_netlink.c:1894)
    __sock_sendmsg (net/socket.c:727 (discriminator 1) net/socket.c:742 (discriminator 1))
    __sys_sendto (./include/linux/file.h:62 (discriminator 1) ./include/linux/file.h:83 (discriminator 1) net/socket.c:2183 (discriminator 1))
    __x64_sys_sendto (net/socket.c:2213 (discriminator 1) net/socket.c:2209 (discriminator 1) net/socket.c:2209 (discriminator 1))
    do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1))
    entry_SYSCALL_64_after_hwframe (net/arch/x86/entry/entry_64.S:130)

This patch makes udp_sock_create6 return -EPFNOSUPPORT instead, so
callers correctly take their error paths. There is only one caller of
the vulnerable function and only privileged users can trigger it.

Fixes: fd384412e199b ("udp_tunnel: Seperate ipv6 functions into its own file.")
Reported-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Xiang Mei <xmei5@asu.edu>
Link: https://patch.msgid.link/20260317010241.1893893-1-xmei5@asu.edu
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
net/sched: Only allow act_ct to bind to clsact/ingress qdiscs and shared blocks 2026-04-18T08:33:11+00:00 Victor Nogueira victor@mojatatu.com 2026-02-25T13:43:48+00:00 bc4e5bb529823a09f02dbe96169de679a9db26e0 commit 11cb63b0d1a0685e0831ae3c77223e002ef18189 upstream. As Paolo said earlier [1]: "Since the blamed commit below, classify can return TC_ACT_CONSUMED while the current skb being held by the defragmentation engine. As reported by GangMin Kim, if such packet is that may cause a UaF when the defrag engine later on tries to tuch again such packet." act_ct was never meant to be used in the egress path, however some users are attaching it to egress today [2]. Attempting to reach a middle ground, we noticed that, while most qdiscs are not handling TC_ACT_CONSUMED, clsact/ingress qdiscs are. With that in mind, we address the issue by only allowing act_ct to bind to clsact/ingress qdiscs and shared blocks. That way it's still possible to attach act_ct to egress (albeit only with clsact). [1] https://lore.kernel.org/netdev/674b8cbfc385c6f37fb29a1de08d8fe5c2b0fbee.1771321118.git.pabeni@redhat.com/ [2] https://lore.kernel.org/netdev/cc6bfb4a-4a2b-42d8-b9ce-7ef6644fb22b@ovn.org/ Reported-by: GangMin Kim <km.kim1503@gmail.com> Fixes: 3f14b377d01d ("net/sched: act_ct: fix skb leak and crash on ooo frags") CC: stable@vger.kernel.org Signed-off-by: Victor Nogueira <victor@mojatatu.com> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com> Link: https://patch.msgid.link/20260225134349.1287037-1-victor@mojatatu.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 11cb63b0d1a0685e0831ae3c77223e002ef18189 upstream.

As Paolo said earlier [1]:

"Since the blamed commit below, classify can return TC_ACT_CONSUMED while
the current skb being held by the defragmentation engine. As reported by
GangMin Kim, if such packet is that may cause a UaF when the defrag engine
later on tries to tuch again such packet."

act_ct was never meant to be used in the egress path, however some users
are attaching it to egress today [2]. Attempting to reach a middle
ground, we noticed that, while most qdiscs are not handling
TC_ACT_CONSUMED, clsact/ingress qdiscs are. With that in mind, we
address the issue by only allowing act_ct to bind to clsact/ingress
qdiscs and shared blocks. That way it's still possible to attach act_ct to
egress (albeit only with clsact).

[1] https://lore.kernel.org/netdev/674b8cbfc385c6f37fb29a1de08d8fe5c2b0fbee.1771321118.git.pabeni@redhat.com/
[2] https://lore.kernel.org/netdev/cc6bfb4a-4a2b-42d8-b9ce-7ef6644fb22b@ovn.org/

Reported-by: GangMin Kim <km.kim1503@gmail.com>
Fixes: 3f14b377d01d ("net/sched: act_ct: fix skb leak and crash on ooo frags")
CC: stable@vger.kernel.org
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20260225134349.1287037-1-victor@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
net: sched: avoid qdisc_reset_all_tx_gt() vs dequeue race for lockless qdiscs 2026-04-18T08:33:10+00:00 Koichiro Den den@valinux.co.jp 2026-02-28T14:53:07+00:00 5bb27ad54d12de67e457d7d251198e361bef835e [ Upstream commit 7f083faf59d14c04e01ec05a7507f036c965acf8 ] When shrinking the number of real tx queues, netif_set_real_num_tx_queues() calls qdisc_reset_all_tx_gt() to flush qdiscs for queues which will no longer be used. qdisc_reset_all_tx_gt() currently serializes qdisc_reset() with qdisc_lock(). However, for lockless qdiscs, the dequeue path is serialized by qdisc_run_begin/end() using qdisc->seqlock instead, so qdisc_reset() can run concurrently with __qdisc_run() and free skbs while they are still being dequeued, leading to UAF. This can easily be reproduced on e.g. virtio-net by imposing heavy traffic while frequently changing the number of queue pairs: iperf3 -ub0 -c $peer -t 0 & while :; do ethtool -L eth0 combined 1 ethtool -L eth0 combined 2 done With KASAN enabled, this leads to reports like: BUG: KASAN: slab-use-after-free in __qdisc_run+0x133f/0x1760 ... Call Trace: <TASK> ... __qdisc_run+0x133f/0x1760 __dev_queue_xmit+0x248f/0x3550 ip_finish_output2+0xa42/0x2110 ip_output+0x1a7/0x410 ip_send_skb+0x2e6/0x480 udp_send_skb+0xb0a/0x1590 udp_sendmsg+0x13c9/0x1fc0 ... </TASK> Allocated by task 1270 on cpu 5 at 44.558414s: ... alloc_skb_with_frags+0x84/0x7c0 sock_alloc_send_pskb+0x69a/0x830 __ip_append_data+0x1b86/0x48c0 ip_make_skb+0x1e8/0x2b0 udp_sendmsg+0x13a6/0x1fc0 ... Freed by task 1306 on cpu 3 at 44.558445s: ... kmem_cache_free+0x117/0x5e0 pfifo_fast_reset+0x14d/0x580 qdisc_reset+0x9e/0x5f0 netif_set_real_num_tx_queues+0x303/0x840 virtnet_set_channels+0x1bf/0x260 [virtio_net] ethnl_set_channels+0x684/0xae0 ethnl_default_set_doit+0x31a/0x890 ... Serialize qdisc_reset_all_tx_gt() against the lockless dequeue path by taking qdisc->seqlock for TCQ_F_NOLOCK qdiscs, matching the serialization model already used by dev_reset_queue(). Additionally clear QDISC_STATE_NON_EMPTY after reset so the qdisc state reflects an empty queue, avoiding needless re-scheduling. Fixes: 6b3ba9146fe6 ("net: sched: allow qdiscs to handle locking") Signed-off-by: Koichiro Den <den@valinux.co.jp> Link: https://patch.msgid.link/20260228145307.3955532-1-den@valinux.co.jp Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 7f083faf59d14c04e01ec05a7507f036c965acf8 ]

When shrinking the number of real tx queues,
netif_set_real_num_tx_queues() calls qdisc_reset_all_tx_gt() to flush
qdiscs for queues which will no longer be used.

qdisc_reset_all_tx_gt() currently serializes qdisc_reset() with
qdisc_lock(). However, for lockless qdiscs, the dequeue path is
serialized by qdisc_run_begin/end() using qdisc->seqlock instead, so
qdisc_reset() can run concurrently with __qdisc_run() and free skbs
while they are still being dequeued, leading to UAF.

This can easily be reproduced on e.g. virtio-net by imposing heavy
traffic while frequently changing the number of queue pairs:

  iperf3 -ub0 -c $peer -t 0 &
  while :; do
    ethtool -L eth0 combined 1
    ethtool -L eth0 combined 2
  done

With KASAN enabled, this leads to reports like:

  BUG: KASAN: slab-use-after-free in __qdisc_run+0x133f/0x1760
  ...
  Call Trace:
   <TASK>
   ...
   __qdisc_run+0x133f/0x1760
   __dev_queue_xmit+0x248f/0x3550
   ip_finish_output2+0xa42/0x2110
   ip_output+0x1a7/0x410
   ip_send_skb+0x2e6/0x480
   udp_send_skb+0xb0a/0x1590
   udp_sendmsg+0x13c9/0x1fc0
   ...
   </TASK>

  Allocated by task 1270 on cpu 5 at 44.558414s:
   ...
   alloc_skb_with_frags+0x84/0x7c0
   sock_alloc_send_pskb+0x69a/0x830
   __ip_append_data+0x1b86/0x48c0
   ip_make_skb+0x1e8/0x2b0
   udp_sendmsg+0x13a6/0x1fc0
   ...

  Freed by task 1306 on cpu 3 at 44.558445s:
   ...
   kmem_cache_free+0x117/0x5e0
   pfifo_fast_reset+0x14d/0x580
   qdisc_reset+0x9e/0x5f0
   netif_set_real_num_tx_queues+0x303/0x840
   virtnet_set_channels+0x1bf/0x260 [virtio_net]
   ethnl_set_channels+0x684/0xae0
   ethnl_default_set_doit+0x31a/0x890
   ...

Serialize qdisc_reset_all_tx_gt() against the lockless dequeue path by
taking qdisc->seqlock for TCQ_F_NOLOCK qdiscs, matching the
serialization model already used by dev_reset_queue().

Additionally clear QDISC_STATE_NON_EMPTY after reset so the qdisc state
reflects an empty queue, avoiding needless re-scheduling.

Fixes: 6b3ba9146fe6 ("net: sched: allow qdiscs to handle locking")
Signed-off-by: Koichiro Den <den@valinux.co.jp>
Link: https://patch.msgid.link/20260228145307.3955532-1-den@valinux.co.jp
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>