In the Linux kernel, the following vulnerability has been resolved:net_sched: sch_sfq: don't allow 1 packet limitThe current implementation does not work correctly with a limit ofiproute2 actually checks for this and this patch adds the check in
kernel as well.This fixes the following syzkaller reported crash:UBSAN: array-index-out-of-bounds in net/sched/sch_sfq.c:210:6
index 65535 is out of range for type 'struct sfq_head[128]'
CPU: 0 PID: 2569 Comm: syz-executor101 Not tainted 5.10.0-smp-DEV #1
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
  __dump_stack lib/dump_stack.c:79 [inline]
  dump_stack+0x125/0x19f lib/dump_stack.c:120
  ubsan_epilogue lib/ubsan.c:148 [inline]
  __ubsan_handle_out_of_bounds+0xed/0x120 lib/ubsan.c:347
  sfq_link net/sched/sch_sfq.c:210 [inline]
  sfq_dec+0x528/0x600 net/sched/sch_sfq.c:238
  sfq_dequeue+0x39b/0x9d0 net/sched/sch_sfq.c:500
  sfq_reset+0x13/0x50 net/sched/sch_sfq.c:525
  qdisc_reset+0xfe/0x510 net/sched/sch_generic.c:1026
  tbf_reset+0x3d/0x100 net/sched/sch_tbf.c:319
  qdisc_reset+0xfe/0x510 net/sched/sch_generic.c:1026
  dev_reset_queue+0x8c/0x140 net/sched/sch_generic.c:1296
  netdev_for_each_tx_queue include/linux/netdevice.h:2350 [inline]
  dev_deactivate_many+0x6dc/0xc20 net/sched/sch_generic.c:1362
  __dev_close_many+0x214/0x350 net/core/dev.c:1468
  dev_close_many+0x207/0x510 net/core/dev.c:1506
  unregister_netdevice_many+0x40f/0x16b0 net/core/dev.c:10738
  unregister_netdevice_queue+0x2be/0x310 net/core/dev.c:10695
  unregister_netdevice include/linux/netdevice.h:2893 [inline]
  __tun_detach+0x6b6/0x1600 drivers/net/tun.c:689
  tun_detach drivers/net/tun.c:705 [inline]
  tun_chr_close+0x104/0x1b0 drivers/net/tun.c:3640
  __fput+0x203/0x840 fs/file_table.c:280
  task_work_run+0x129/0x1b0 kernel/task_work.c:185
  exit_task_work include/linux/task_work.h:33 [inline]
  do_exit+0x5ce/0x2200 kernel/exit.c:931
  do_group_exit+0x144/0x310 kernel/exit.c:1046
  __do_sys_exit_group kernel/exit.c:1057 [inline]
  __se_sys_exit_group kernel/exit.c:1055 [inline]
  __x64_sys_exit_group+0x3b/0x40 kernel/exit.c:1055
 do_syscall_64+0x6c/0xd0
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7fe5e7b52479
Code: Unable to access opcode bytes at RIP 0x7fe5e7b5244f.
RSP: 002b:00007ffd3c800398 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fe5e7b52479
RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000000
RBP: 00007fe5e7bcd2d0 R08: ffffffffffffffb8 R09: 0000000000000014
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fe5e7bcd2d0
R13: 0000000000000000 R14: 00007fe5e7bcdd20 R15: 00007fe5e7b24270The crash can be also be reproduced with the following (with a tc
recompiled to allow for sfq limits of 1):tc qdisc add dev dummy0 handle 1: root tbf rate 1Kbit burst 100b lat 1s
../iproute2-6.9.0/tc/tc qdisc add dev dummy0 handle 2: parent 1:10 sfq limit 1
ifconfig dummy0 up
ping -I dummy0 -f -c2 -W0.1 8.8.8.8
sleep 1Scenario that triggers the crash:the first packet is sent and queued in TBF and SFQ; qdisc qlen is 1TBF dequeues: it peeks from SFQ which moves the packet to the
gso_skb list and keeps qdisc qlen set to 1. TBF is out of tokens so
it schedules itself for later.the second packet is sent and TBF tries to queues it to SFQ. qdisc
qlen is now 2 and because the SFQ limit is 1 the packet is dropped
by SFQ. At this point qlen is 1, and all of the SFQ slots are empty,
however q->tail is not NULL.At this point, assuming no more packets are queued, when sch_dequeue
runs again it will decrement the qlen for the current empty slot
causing an underflow and the subsequent out of bounds access.