linux.git/net, branch v6.11

net: netfilter: move nf flowtable bpf initialization in nf_flow_table_module_init()

2024-09-12T13:41:03+00:00

Move nf flowtable bpf initialization in nf_flow_table module load
routine since nf_flow_table_bpf is part of nf_flow_table module and not
nf_flow_table_inet one. This patch allows to avoid the following kernel
warning running the reproducer below:

$modprobe nf_flow_table_inet
$rmmod nf_flow_table_inet
$modprobe nf_flow_table_inet
modprobe: ERROR: could not insert 'nf_flow_table_inet': Invalid argument

[  184.081501] ------------[ cut here ]------------
[  184.081527] WARNING: CPU: 0 PID: 1362 at kernel/bpf/btf.c:8206 btf_populate_kfunc_set+0x23c/0x330
[  184.081550] CPU: 0 UID: 0 PID: 1362 Comm: modprobe Kdump: loaded Not tainted 6.11.0-0.rc5.22.el10.x86_64 #1
[  184.081553] Hardware name: Red Hat OpenStack Compute, BIOS 1.14.0-1.module+el8.4.0+8855+a9e237a9 04/01/2014
[  184.081554] RIP: 0010:btf_populate_kfunc_set+0x23c/0x330
[  184.081558] RSP: 0018:ff22cfb38071fc90 EFLAGS: 00010202
[  184.081559] RAX: 0000000000000001 RBX: 0000000000000001 RCX: 0000000000000000
[  184.081560] RDX: 000000000000006e RSI: ffffffff95c00000 RDI: ff13805543436350
[  184.081561] RBP: ffffffffc0e22180 R08: ff13805543410808 R09: 000000000001ec00
[  184.081562] R10: ff13805541c8113c R11: 0000000000000010 R12: ff13805541b83c00
[  184.081563] R13: ff13805543410800 R14: 0000000000000001 R15: ffffffffc0e2259a
[  184.081564] FS:  00007fa436c46740(0000) GS:ff1380557ba00000(0000) knlGS:0000000000000000
[  184.081569] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  184.081570] CR2: 000055e7b3187000 CR3: 0000000100c48003 CR4: 0000000000771ef0
[  184.081571] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  184.081572] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  184.081572] PKRU: 55555554
[  184.081574] Call Trace:
[  184.081575]  
[  184.081578]  ? show_trace_log_lvl+0x1b0/0x2f0
[  184.081580]  ? show_trace_log_lvl+0x1b0/0x2f0
[  184.081582]  ? __register_btf_kfunc_id_set+0x199/0x200
[  184.081585]  ? btf_populate_kfunc_set+0x23c/0x330
[  184.081586]  ? __warn.cold+0x93/0xed
[  184.081590]  ? btf_populate_kfunc_set+0x23c/0x330
[  184.081592]  ? report_bug+0xff/0x140
[  184.081594]  ? handle_bug+0x3a/0x70
[  184.081596]  ? exc_invalid_op+0x17/0x70
[  184.081597]  ? asm_exc_invalid_op+0x1a/0x20
[  184.081601]  ? btf_populate_kfunc_set+0x23c/0x330
[  184.081602]  __register_btf_kfunc_id_set+0x199/0x200
[  184.081605]  ? __pfx_nf_flow_inet_module_init+0x10/0x10 [nf_flow_table_inet]
[  184.081607]  do_one_initcall+0x58/0x300
[  184.081611]  do_init_module+0x60/0x230
[  184.081614]  __do_sys_init_module+0x17a/0x1b0
[  184.081617]  do_syscall_64+0x7d/0x160
[  184.081620]  ? __count_memcg_events+0x58/0xf0
[  184.081623]  ? handle_mm_fault+0x234/0x350
[  184.081626]  ? do_user_addr_fault+0x347/0x640
[  184.081630]  ? clear_bhb_loop+0x25/0x80
[  184.081633]  ? clear_bhb_loop+0x25/0x80
[  184.081634]  ? clear_bhb_loop+0x25/0x80
[  184.081637]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[  184.081639] RIP: 0033:0x7fa43652e4ce
[  184.081647] RSP: 002b:00007ffe8213be18 EFLAGS: 00000246 ORIG_RAX: 00000000000000af
[  184.081649] RAX: ffffffffffffffda RBX: 000055e7b3176c20 RCX: 00007fa43652e4ce
[  184.081650] RDX: 000055e7737fde79 RSI: 0000000000003990 RDI: 000055e7b3185380
[  184.081651] RBP: 000055e7737fde79 R08: 0000000000000007 R09: 000055e7b3179bd0
[  184.081651] R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000040000
[  184.081652] R13: 000055e7b3176fa0 R14: 0000000000000000 R15: 000055e7b3179b80

Fixes: 391bb6594fd3 ("netfilter: Add bpf_xdp_flow_lookup kfunc")
Signed-off-by: Lorenzo Bianconi 
Acked-by: Florian Westphal 
Acked-by: Pablo Neira Ayuso 
Link: https://patch.msgid.link/20240911-nf-flowtable-bpf-modprob-fix-v1-1-f9fc075aafc3@kernel.org
Signed-off-by: Paolo Abeni

Merge tag 'nf-24-09-12' of git://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf

2024-09-12T13:26:19+00:00

Pablo Neira Ayuso says:

====================
Netfilter fixes for net

The following batch contains two fixes from Florian Westphal:

Patch #1 fixes a sk refcount leak in nft_socket on mismatch.

Patch #2 fixes cgroupsv2 matching from containers due to incorrect
	 level in subtree.

netfilter pull request 24-09-12

* tag 'nf-24-09-12' of git://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf:
  netfilter: nft_socket: make cgroupsv2 matching work with namespaces
  netfilter: nft_socket: fix sk refcount leaks
====================

Link: https://patch.msgid.link/20240911222520.3606-1-pablo@netfilter.org
Signed-off-by: Paolo Abeni

mptcp: pm: Fix uaf in __timer_delete_sync

2024-09-11T23:00:11+00:00

There are two paths to access mptcp_pm_del_add_timer, result in a race
condition:

     CPU1				CPU2
     ====                               ====
     net_rx_action
     napi_poll                          netlink_sendmsg
     __napi_poll                        netlink_unicast
     process_backlog                    netlink_unicast_kernel
     __netif_receive_skb                genl_rcv
     __netif_receive_skb_one_core       netlink_rcv_skb
     NF_HOOK                            genl_rcv_msg
     ip_local_deliver_finish            genl_family_rcv_msg
     ip_protocol_deliver_rcu            genl_family_rcv_msg_doit
     tcp_v4_rcv                         mptcp_pm_nl_flush_addrs_doit
     tcp_v4_do_rcv                      mptcp_nl_remove_addrs_list
     tcp_rcv_established                mptcp_pm_remove_addrs_and_subflows
     tcp_data_queue                     remove_anno_list_by_saddr
     mptcp_incoming_options             mptcp_pm_del_add_timer
     mptcp_pm_del_add_timer             kfree(entry)

In remove_anno_list_by_saddr(running on CPU2), after leaving the critical
zone protected by "pm.lock", the entry will be released, which leads to the
occurrence of uaf in the mptcp_pm_del_add_timer(running on CPU1).

Keeping a reference to add_timer inside the lock, and calling
sk_stop_timer_sync() with this reference, instead of "entry->add_timer".

Move list_del(&entry->list) to mptcp_pm_del_add_timer and inside the pm lock,
do not directly access any members of the entry outside the pm lock, which
can avoid similar "entry->x" uaf.

Fixes: 00cfd77b9063 ("mptcp: retransmit ADD_ADDR when timeout")
Cc: stable@vger.kernel.org
Reported-and-tested-by: syzbot+f3a31fb909db9b2a5c4d@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f3a31fb909db9b2a5c4d
Signed-off-by: Matthieu Baerts (NGI0) 
Signed-off-by: Edward Adam Davis 
Acked-by: Paolo Abeni 
Link: https://patch.msgid.link/tencent_7142963A37944B4A74EF76CD66EA3C253609@qq.com
Signed-off-by: Jakub Kicinski

net: hsr: prevent NULL pointer dereference in hsr_proxy_announce()

2024-09-11T22:49:41+00:00

In the function hsr_proxy_annouance() added in the previous commit
5f703ce5c981 ("net: hsr: Send supervisory frames to HSR network
with ProxyNodeTable data"), the return value of the hsr_port_get_hsr()
function is not checked to be a NULL pointer, which causes a NULL
pointer dereference.

To solve this, we need to add code to check whether the return value
of hsr_port_get_hsr() is NULL.

Reported-by: syzbot+02a42d9b1bd395cbcab4@syzkaller.appspotmail.com
Fixes: 5f703ce5c981 ("net: hsr: Send supervisory frames to HSR network with ProxyNodeTable data")
Signed-off-by: Jeongjun Park 
Reviewed-by: Simon Horman 
Acked-by: Lukasz Majewski 
Link: https://patch.msgid.link/20240907190341.162289-1-aha310510@gmail.com
Signed-off-by: Jakub Kicinski

netfilter: nft_socket: make cgroupsv2 matching work with namespaces

2024-09-11T22:16:58+00:00

When running in container environmment, /sys/fs/cgroup/ might not be
the real root node of the sk-attached cgroup.

Example:

In container:
% stat /sys//fs/cgroup/
Device: 0,21    Inode: 2214  ..
% stat /sys/fs/cgroup/foo
Device: 0,21    Inode: 2264  ..

The expectation would be for:

  nft add rule .. socket cgroupv2 level 1 "foo" counter

to match traffic from a process that got added to "foo" via
"echo $pid > /sys/fs/cgroup/foo/cgroup.procs".

However, 'level 3' is needed to make this work.

Seen from initial namespace, the complete hierarchy is:

% stat /sys/fs/cgroup/system.slice/docker-.../foo
  Device: 0,21    Inode: 2264 ..

i.e. hierarchy is
0    1               2              3
/ -> system.slice -> docker-1... -> foo

... but the container doesn't know that its "/" is the "docker-1.."
cgroup.  Current code will retrieve the 'system.slice' cgroup node
and store its kn->id in the destination register, so compare with
2264 ("foo" cgroup id) will not match.

Fetch "/" cgroup from ->init() and add its level to the level we try to
extract.  cgroup root-level is 0 for the init-namespace or the level
of the ancestor that is exposed as the cgroup root inside the container.

In the above case, cgrp->level of "/" resolved in the container is 2
(docker-1...scope/) and request for 'level 1' will get adjusted
to fetch the actual level (3).

v2: use CONFIG_SOCK_CGROUP_DATA, eval function depends on it.
    (kernel test robot)

Cc: cgroups@vger.kernel.org
Fixes: e0bb96db96f8 ("netfilter: nft_socket: add support for cgroupsv2")
Reported-by: Nadia Pinaeva 
Signed-off-by: Florian Westphal 
Signed-off-by: Pablo Neira Ayuso

netfilter: nft_socket: fix sk refcount leaks

2024-09-11T22:16:54+00:00

We must put 'sk' reference before returning.

Fixes: 039b1f4f24ec ("netfilter: nft_socket: fix erroneous socket assignment")
Signed-off-by: Florian Westphal 
Signed-off-by: Pablo Neira Ayuso

fou: fix initialization of grc

2024-09-10T00:21:47+00:00

The grc must be initialize first. There can be a condition where if
fou is NULL, goto out will be executed and grc would be used
uninitialized.

Fixes: 7e4196935069 ("fou: Fix null-ptr-deref in GRO.")
Signed-off-by: Muhammad Usama Anjum 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20240906102839.202798-1-usama.anjum@collabora.com
Signed-off-by: Jakub Kicinski

net: hsr: remove seqnr_lock

2024-09-09T09:25:01+00:00

syzbot found a new splat [1].

Instead of adding yet another spin_lock_bh(&hsr->seqnr_lock) /
spin_unlock_bh(&hsr->seqnr_lock) pair, remove seqnr_lock
and use atomic_t for hsr->sequence_nr and hsr->sup_sequence_nr.

This also avoid a race in hsr_fill_info().

Also remove interlink_sequence_nr which is unused.

[1]
 WARNING: CPU: 1 PID: 9723 at net/hsr/hsr_forward.c:602 handle_std_frame+0x247/0x2c0 net/hsr/hsr_forward.c:602
Modules linked in:
CPU: 1 UID: 0 PID: 9723 Comm: syz.0.1657 Not tainted 6.11.0-rc6-syzkaller-00026-g88fac17500f4 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
 RIP: 0010:handle_std_frame+0x247/0x2c0 net/hsr/hsr_forward.c:602
Code: 49 8d bd b0 01 00 00 be ff ff ff ff e8 e2 58 25 00 31 ff 89 c5 89 c6 e8 47 53 a8 f6 85 ed 0f 85 5a ff ff ff e8 fa 50 a8 f6 90 <0f> 0b 90 e9 4c ff ff ff e8 cc e7 06 f7 e9 8f fe ff ff e8 52 e8 06
RSP: 0018:ffffc90000598598 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffffc90000598670 RCX: ffffffff8ae2c919
RDX: ffff888024e94880 RSI: ffffffff8ae2c926 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000003
R13: ffff8880627a8cc0 R14: 0000000000000000 R15: ffff888012b03c3a
FS:  0000000000000000(0000) GS:ffff88802b700000(0063) knlGS:00000000f5696b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000020010000 CR3: 00000000768b4000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 
  hsr_fill_frame_info+0x2c8/0x360 net/hsr/hsr_forward.c:630
  fill_frame_info net/hsr/hsr_forward.c:700 [inline]
  hsr_forward_skb+0x7df/0x25c0 net/hsr/hsr_forward.c:715
  hsr_handle_frame+0x603/0x850 net/hsr/hsr_slave.c:70
  __netif_receive_skb_core.constprop.0+0xa3d/0x4330 net/core/dev.c:5555
  __netif_receive_skb_list_core+0x357/0x950 net/core/dev.c:5737
  __netif_receive_skb_list net/core/dev.c:5804 [inline]
  netif_receive_skb_list_internal+0x753/0xda0 net/core/dev.c:5896
  gro_normal_list include/net/gro.h:515 [inline]
  gro_normal_list include/net/gro.h:511 [inline]
  napi_complete_done+0x23f/0x9a0 net/core/dev.c:6247
  gro_cell_poll+0x162/0x210 net/core/gro_cells.c:66
  __napi_poll.constprop.0+0xb7/0x550 net/core/dev.c:6772
  napi_poll net/core/dev.c:6841 [inline]
  net_rx_action+0xa92/0x1010 net/core/dev.c:6963
  handle_softirqs+0x216/0x8f0 kernel/softirq.c:554
  do_softirq kernel/softirq.c:455 [inline]
  do_softirq+0xb2/0xf0 kernel/softirq.c:442
 
 

Fixes: 06afd2c31d33 ("hsr: Synchronize sending frames to have always incremented outgoing seq nr.")
Fixes: f421436a591d ("net/hsr: Add support for the High-availability Seamless Redundancy protocol (HSRv0)")
Reported-by: syzbot 
Signed-off-by: Eric Dumazet 
Cc: Sebastian Andrzej Siewior 
Reviewed-by: Simon Horman 
Signed-off-by: David S. Miller

ila: call nf_unregister_net_hooks() sooner

2024-09-05T21:57:12+00:00

syzbot found an use-after-free Read in ila_nf_input [1]

Issue here is that ila_xlat_exit_net() frees the rhashtable,
then call nf_unregister_net_hooks().

It should be done in the reverse way, with a synchronize_rcu().

This is a good match for a pre_exit() method.

[1]
 BUG: KASAN: use-after-free in rht_key_hashfn include/linux/rhashtable.h:159 [inline]
 BUG: KASAN: use-after-free in __rhashtable_lookup include/linux/rhashtable.h:604 [inline]
 BUG: KASAN: use-after-free in rhashtable_lookup include/linux/rhashtable.h:646 [inline]
 BUG: KASAN: use-after-free in rhashtable_lookup_fast+0x77a/0x9b0 include/linux/rhashtable.h:672
Read of size 4 at addr ffff888064620008 by task ksoftirqd/0/16

CPU: 0 UID: 0 PID: 16 Comm: ksoftirqd/0 Not tainted 6.11.0-rc4-syzkaller-00238-g2ad6d23f465a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
Call Trace:
 
  __dump_stack lib/dump_stack.c:93 [inline]
  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:119
  print_address_description mm/kasan/report.c:377 [inline]
  print_report+0x169/0x550 mm/kasan/report.c:488
  kasan_report+0x143/0x180 mm/kasan/report.c:601
  rht_key_hashfn include/linux/rhashtable.h:159 [inline]
  __rhashtable_lookup include/linux/rhashtable.h:604 [inline]
  rhashtable_lookup include/linux/rhashtable.h:646 [inline]
  rhashtable_lookup_fast+0x77a/0x9b0 include/linux/rhashtable.h:672
  ila_lookup_wildcards net/ipv6/ila/ila_xlat.c:132 [inline]
  ila_xlat_addr net/ipv6/ila/ila_xlat.c:652 [inline]
  ila_nf_input+0x1fe/0x3c0 net/ipv6/ila/ila_xlat.c:190
  nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
  nf_hook_slow+0xc3/0x220 net/netfilter/core.c:626
  nf_hook include/linux/netfilter.h:269 [inline]
  NF_HOOK+0x29e/0x450 include/linux/netfilter.h:312
  __netif_receive_skb_one_core net/core/dev.c:5661 [inline]
  __netif_receive_skb+0x1ea/0x650 net/core/dev.c:5775
  process_backlog+0x662/0x15b0 net/core/dev.c:6108
  __napi_poll+0xcb/0x490 net/core/dev.c:6772
  napi_poll net/core/dev.c:6841 [inline]
  net_rx_action+0x89b/0x1240 net/core/dev.c:6963
  handle_softirqs+0x2c4/0x970 kernel/softirq.c:554
  run_ksoftirqd+0xca/0x130 kernel/softirq.c:928
  smpboot_thread_fn+0x544/0xa30 kernel/smpboot.c:164
  kthread+0x2f0/0x390 kernel/kthread.c:389
  ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x64620
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xbfffffff(buddy)
raw: 00fff00000000000 ffffea0000959608 ffffea00019d9408 0000000000000000
raw: 0000000000000000 0000000000000003 00000000bfffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x52dc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_ZERO), pid 5242, tgid 5242 (syz-executor), ts 73611328570, free_ts 618981657187
  set_page_owner include/linux/page_owner.h:32 [inline]
  post_alloc_hook+0x1f3/0x230 mm/page_alloc.c:1493
  prep_new_page mm/page_alloc.c:1501 [inline]
  get_page_from_freelist+0x2e4c/0x2f10 mm/page_alloc.c:3439
  __alloc_pages_noprof+0x256/0x6c0 mm/page_alloc.c:4695
  __alloc_pages_node_noprof include/linux/gfp.h:269 [inline]
  alloc_pages_node_noprof include/linux/gfp.h:296 [inline]
  ___kmalloc_large_node+0x8b/0x1d0 mm/slub.c:4103
  __kmalloc_large_node_noprof+0x1a/0x80 mm/slub.c:4130
  __do_kmalloc_node mm/slub.c:4146 [inline]
  __kmalloc_node_noprof+0x2d2/0x440 mm/slub.c:4164
  __kvmalloc_node_noprof+0x72/0x190 mm/util.c:650
  bucket_table_alloc lib/rhashtable.c:186 [inline]
  rhashtable_init_noprof+0x534/0xa60 lib/rhashtable.c:1071
  ila_xlat_init_net+0xa0/0x110 net/ipv6/ila/ila_xlat.c:613
  ops_init+0x359/0x610 net/core/net_namespace.c:139
  setup_net+0x515/0xca0 net/core/net_namespace.c:343
  copy_net_ns+0x4e2/0x7b0 net/core/net_namespace.c:508
  create_new_namespaces+0x425/0x7b0 kernel/nsproxy.c:110
  unshare_nsproxy_namespaces+0x124/0x180 kernel/nsproxy.c:228
  ksys_unshare+0x619/0xc10 kernel/fork.c:3328
  __do_sys_unshare kernel/fork.c:3399 [inline]
  __se_sys_unshare kernel/fork.c:3397 [inline]
  __x64_sys_unshare+0x38/0x40 kernel/fork.c:3397
page last free pid 11846 tgid 11846 stack trace:
  reset_page_owner include/linux/page_owner.h:25 [inline]
  free_pages_prepare mm/page_alloc.c:1094 [inline]
  free_unref_page+0xd22/0xea0 mm/page_alloc.c:2612
  __folio_put+0x2c8/0x440 mm/swap.c:128
  folio_put include/linux/mm.h:1486 [inline]
  free_large_kmalloc+0x105/0x1c0 mm/slub.c:4565
  kfree+0x1c4/0x360 mm/slub.c:4588
  rhashtable_free_and_destroy+0x7c6/0x920 lib/rhashtable.c:1169
  ila_xlat_exit_net+0x55/0x110 net/ipv6/ila/ila_xlat.c:626
  ops_exit_list net/core/net_namespace.c:173 [inline]
  cleanup_net+0x802/0xcc0 net/core/net_namespace.c:640
  process_one_work kernel/workqueue.c:3231 [inline]
  process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
  worker_thread+0x86d/0xd40 kernel/workqueue.c:3390
  kthread+0x2f0/0x390 kernel/kthread.c:389
  ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Memory state around the buggy address:
 ffff88806461ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88806461ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888064620000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                      ^
 ffff888064620080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888064620100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

Fixes: 7f00feaf1076 ("ila: Add generic ILA translation facility")
Reported-by: syzbot 
Signed-off-by: Eric Dumazet 
Cc: Tom Herbert 
Reviewed-by: Florian Westphal 
Link: https://patch.msgid.link/20240904144418.1162839-1-edumazet@google.com
Signed-off-by: Jakub Kicinski

sched: sch_cake: fix bulk flow accounting logic for host fairness

2024-09-05T09:49:57+00:00

In sch_cake, we keep track of the count of active bulk flows per host,
when running in dst/src host fairness mode, which is used as the
round-robin weight when iterating through flows. The count of active
bulk flows is updated whenever a flow changes state.

This has a peculiar interaction with the hash collision handling: when a
hash collision occurs (after the set-associative hashing), the state of
the hash bucket is simply updated to match the new packet that collided,
and if host fairness is enabled, that also means assigning new per-host
state to the flow. For this reason, the bulk flow counters of the
host(s) assigned to the flow are decremented, before new state is
assigned (and the counters, which may not belong to the same host
anymore, are incremented again).

Back when this code was introduced, the host fairness mode was always
enabled, so the decrement was unconditional. When the configuration
flags were introduced the *increment* was made conditional, but
the *decrement* was not. Which of course can lead to a spurious
decrement (and associated wrap-around to U16_MAX).

AFAICT, when host fairness is disabled, the decrement and wrap-around
happens as soon as a hash collision occurs (which is not that common in
itself, due to the set-associative hashing). However, in most cases this
is harmless, as the value is only used when host fairness mode is
enabled. So in order to trigger an array overflow, sch_cake has to first
be configured with host fairness disabled, and while running in this
mode, a hash collision has to occur to cause the overflow. Then, the
qdisc has to be reconfigured to enable host fairness, which leads to the
array out-of-bounds because the wrapped-around value is retained and
used as an array index. It seems that syzbot managed to trigger this,
which is quite impressive in its own right.

This patch fixes the issue by introducing the same conditional check on
decrement as is used on increment.

The original bug predates the upstreaming of cake, but the commit listed
in the Fixes tag touched that code, meaning that this patch won't apply
before that.

Fixes: 712639929912 ("sch_cake: Make the dual modes fairer")
Reported-by: syzbot+7fe7b81d602cc1e6b94d@syzkaller.appspotmail.com
Signed-off-by: Toke Høiland-Jørgensen 
Link: https://patch.msgid.link/20240903160846.20909-1-toke@redhat.com
Signed-off-by: Paolo Abeni