Packet dropped counter in dualpi2 AQM #7
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Hi,
I tried to count the numbers of drops in your dualpi2 aqm located at this
link :
https://github.com/L4STeam/linux/blob/testing/net/sched/sch_dualpi2.c
For this I looked in the source code and I saw this parameter named cnt
in this struct
struct { /* Deferred drop statistics */ u32 cnt; /* Packets dropped */
u32 len; /* Bytes dropped */ } deferred_drops;
For me this variable counts the total number of drop in both queues
(classic and l4s) in the dualpi2 AQM
when a packet is dropped.
It does not, and its name/usage states it clearly:
https://github.com/L4STeam/linux/blob/testing/net/sched/sch_dualpi2.c#L567
it is only used to defer the propagation of the backlog update
to parent qdiscs.
dualpi2 does not duplicate the drop counter of the base qdisc implementation;
You can find that counter as part of the qstats member of the Qdisc struct:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/net/sch_generic.h#n104
i.e., the one that is increased at every qdisc_drop() call
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/net/sch_generic.h#n1175
or qdisc_qstats_drop()
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/net/sch_generic.h#n897
That is 'dropped' counter that is displayed when doing `tc -s qdisc` (to
be used in conjunction with 'overlimit' to distinguish between the PI2
drops and the taildrop is the queue overflows.
Best,
Olivier
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minuscat
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Dec 26, 2024
[ Upstream commit 3f23f96528e8fcf8619895c4c916c52653892ec1 ] BUG: KASAN: slab-use-after-free in tcp_write_timer_handler+0x156/0x3e0 Read of size 1 at addr ffff888111f322cd by task swapper/0/0 CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.12.0-rc4-dirty #7 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 Call Trace: <IRQ> dump_stack_lvl+0x68/0xa0 print_address_description.constprop.0+0x2c/0x3d0 print_report+0xb4/0x270 kasan_report+0xbd/0xf0 tcp_write_timer_handler+0x156/0x3e0 tcp_write_timer+0x66/0x170 call_timer_fn+0xfb/0x1d0 __run_timers+0x3f8/0x480 run_timer_softirq+0x9b/0x100 handle_softirqs+0x153/0x390 __irq_exit_rcu+0x103/0x120 irq_exit_rcu+0xe/0x20 sysvec_apic_timer_interrupt+0x76/0x90 </IRQ> <TASK> asm_sysvec_apic_timer_interrupt+0x1a/0x20 RIP: 0010:default_idle+0xf/0x20 Code: 4c 01 c7 4c 29 c2 e9 72 ff ff ff 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 33 f8 25 00 fb f4 <fa> c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 RSP: 0018:ffffffffa2007e28 EFLAGS: 00000242 RAX: 00000000000f3b31 RBX: 1ffffffff4400fc7 RCX: ffffffffa09c3196 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff9f00590f RBP: 0000000000000000 R08: 0000000000000001 R09: ffffed102360835d R10: ffff88811b041aeb R11: 0000000000000001 R12: 0000000000000000 R13: ffffffffa202d7c0 R14: 0000000000000000 R15: 00000000000147d0 default_idle_call+0x6b/0xa0 cpuidle_idle_call+0x1af/0x1f0 do_idle+0xbc/0x130 cpu_startup_entry+0x33/0x40 rest_init+0x11f/0x210 start_kernel+0x39a/0x420 x86_64_start_reservations+0x18/0x30 x86_64_start_kernel+0x97/0xa0 common_startup_64+0x13e/0x141 </TASK> Allocated by task 595: kasan_save_stack+0x24/0x50 kasan_save_track+0x14/0x30 __kasan_slab_alloc+0x87/0x90 kmem_cache_alloc_noprof+0x12b/0x3f0 copy_net_ns+0x94/0x380 create_new_namespaces+0x24c/0x500 unshare_nsproxy_namespaces+0x75/0xf0 ksys_unshare+0x24e/0x4f0 __x64_sys_unshare+0x1f/0x30 do_syscall_64+0x70/0x180 entry_SYSCALL_64_after_hwframe+0x76/0x7e Freed by task 100: kasan_save_stack+0x24/0x50 kasan_save_track+0x14/0x30 kasan_save_free_info+0x3b/0x60 __kasan_slab_free+0x54/0x70 kmem_cache_free+0x156/0x5d0 cleanup_net+0x5d3/0x670 process_one_work+0x776/0xa90 worker_thread+0x2e2/0x560 kthread+0x1a8/0x1f0 ret_from_fork+0x34/0x60 ret_from_fork_asm+0x1a/0x30 Reproduction script: mkdir -p /mnt/nfsshare mkdir -p /mnt/nfs/netns_1 mkfs.ext4 /dev/sdb mount /dev/sdb /mnt/nfsshare systemctl restart nfs-server chmod 777 /mnt/nfsshare exportfs -i -o rw,no_root_squash *:/mnt/nfsshare ip netns add netns_1 ip link add name veth_1_peer type veth peer veth_1 ifconfig veth_1_peer 11.11.0.254 up ip link set veth_1 netns netns_1 ip netns exec netns_1 ifconfig veth_1 11.11.0.1 ip netns exec netns_1 /root/iptables -A OUTPUT -d 11.11.0.254 -p tcp \ --tcp-flags FIN FIN -j DROP (note: In my environment, a DESTROY_CLIENTID operation is always sent immediately, breaking the nfs tcp connection.) ip netns exec netns_1 timeout -s 9 300 mount -t nfs -o proto=tcp,vers=4.1 \ 11.11.0.254:/mnt/nfsshare /mnt/nfs/netns_1 ip netns del netns_1 The reason here is that the tcp socket in netns_1 (nfs side) has been shutdown and closed (done in xs_destroy), but the FIN message (with ack) is discarded, and the nfsd side keeps sending retransmission messages. As a result, when the tcp sock in netns_1 processes the received message, it sends the message (FIN message) in the sending queue, and the tcp timer is re-established. When the network namespace is deleted, the net structure accessed by tcp's timer handler function causes problems. To fix this problem, let's hold netns refcnt for the tcp kernel socket as done in other modules. This is an ugly hack which can easily be backported to earlier kernels. A proper fix which cleans up the interfaces will follow, but may not be so easy to backport. Fixes: 26abe14 ("net: Modify sk_alloc to not reference count the netns of kernel sockets.") Signed-off-by: Liu Jian <[email protected]> Acked-by: Jeff Layton <[email protected]> Reviewed-by: Kuniyuki Iwashima <[email protected]> Signed-off-by: Trond Myklebust <[email protected]> Signed-off-by: Sasha Levin <[email protected]>
minuscat
pushed a commit
that referenced
this issue
Dec 26, 2024
[ Upstream commit 6a2fa13312e51a621f652d522d7e2df7066330b6 ]
syzkaller reported a use-after-free of UDP kernel socket
in cleanup_bearer() without repro. [0][1]
When bearer_disable() calls tipc_udp_disable(), cleanup
of the UDP kernel socket is deferred by work calling
cleanup_bearer().
tipc_net_stop() waits for such works to finish by checking
tipc_net(net)->wq_count. However, the work decrements the
count too early before releasing the kernel socket,
unblocking cleanup_net() and resulting in use-after-free.
Let's move the decrement after releasing the socket in
cleanup_bearer().
[0]:
ref_tracker: net notrefcnt@000000009b3d1faf has 1/1 users at
sk_alloc+0x438/0x608
inet_create+0x4c8/0xcb0
__sock_create+0x350/0x6b8
sock_create_kern+0x58/0x78
udp_sock_create4+0x68/0x398
udp_sock_create+0x88/0xc8
tipc_udp_enable+0x5e8/0x848
__tipc_nl_bearer_enable+0x84c/0xed8
tipc_nl_bearer_enable+0x38/0x60
genl_family_rcv_msg_doit+0x170/0x248
genl_rcv_msg+0x400/0x5b0
netlink_rcv_skb+0x1dc/0x398
genl_rcv+0x44/0x68
netlink_unicast+0x678/0x8b0
netlink_sendmsg+0x5e4/0x898
____sys_sendmsg+0x500/0x830
[1]:
BUG: KMSAN: use-after-free in udp_hashslot include/net/udp.h:85 [inline]
BUG: KMSAN: use-after-free in udp_lib_unhash+0x3b8/0x930 net/ipv4/udp.c:1979
udp_hashslot include/net/udp.h:85 [inline]
udp_lib_unhash+0x3b8/0x930 net/ipv4/udp.c:1979
sk_common_release+0xaf/0x3f0 net/core/sock.c:3820
inet_release+0x1e0/0x260 net/ipv4/af_inet.c:437
inet6_release+0x6f/0xd0 net/ipv6/af_inet6.c:489
__sock_release net/socket.c:658 [inline]
sock_release+0xa0/0x210 net/socket.c:686
cleanup_bearer+0x42d/0x4c0 net/tipc/udp_media.c:819
process_one_work kernel/workqueue.c:3229 [inline]
process_scheduled_works+0xcaf/0x1c90 kernel/workqueue.c:3310
worker_thread+0xf6c/0x1510 kernel/workqueue.c:3391
kthread+0x531/0x6b0 kernel/kthread.c:389
ret_from_fork+0x60/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:244
Uninit was created at:
slab_free_hook mm/slub.c:2269 [inline]
slab_free mm/slub.c:4580 [inline]
kmem_cache_free+0x207/0xc40 mm/slub.c:4682
net_free net/core/net_namespace.c:454 [inline]
cleanup_net+0x16f2/0x19d0 net/core/net_namespace.c:647
process_one_work kernel/workqueue.c:3229 [inline]
process_scheduled_works+0xcaf/0x1c90 kernel/workqueue.c:3310
worker_thread+0xf6c/0x1510 kernel/workqueue.c:3391
kthread+0x531/0x6b0 kernel/kthread.c:389
ret_from_fork+0x60/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:244
CPU: 0 UID: 0 PID: 54 Comm: kworker/0:2 Not tainted 6.12.0-rc1-00131-gf66ebf37d69c #7 91723d6f74857f70725e1583cba3cf4adc716cfa
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
Workqueue: events cleanup_bearer
Fixes: 26abe14 ("net: Modify sk_alloc to not reference count the netns of kernel sockets.")
Reported-by: syzkaller <[email protected]>
Signed-off-by: Kuniyuki Iwashima <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
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Hello all,
I tried to count the numbers of drops in your dualpi2 aqm located at this link :
https://github.com/L4STeam/linux/blob/testing/net/sched/sch_dualpi2.cFor this I looked in the source code and I saw this parameter named
cntin this structstruct { /* Deferred drop statistics */ u32 cnt; /* Packets dropped */ u32 len; /* Bytes dropped */ } deferred_drops;For me this variable counts the total number of drop in both queues (classic and l4s) in the dualpi2 AQM
when a packet is dropped.
But what I remarked is that this variable that must count drop is incremented only one time
++q->deferred_drops.cnt;at line596of the dualpi2's source code in the dequeue functionstatic struct sk_buff *dualpi2_qdisc_dequeue(struct Qdisc *sch).What I don't understand is why the drops counters
q->deferred_drops.cntis incremented only one time ?Packet dropping does not happens when there are packet to enqueue and queue limit is reached or drop_early is enable ?
If I mistake, can you show me in the source code where packet dropping happens , please?
Regards
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