TLDRVuln - Cybersecurity Vulnerabilities Made Simple

In the Linux kernel, the following vulnerability has been resolved:

net_sched: sch_sfq: move the limit validation

It is not sufficient to directly validate the limit on the data that

the user passes as it can be updated based on how the other parameters

are changed.

Move the check at the end of the configuration update process to also

catch scenarios where the limit is indirectly updated, for example

with the following configurations:

tc qdisc add dev dummy0 handle 1: root sfq limit 2 flows 1 depth 1

tc qdisc add dev dummy0 handle 1: root sfq limit 2 flows 1 divisor 1

This fixes the following syzkaller reported crash:

------------[ cut here ]------------

UBSAN: array-index-out-of-bounds in net/sched/sch_sfq.c:203:6

index 65535 is out of range for type 'struct sfq_head[128]'

CPU: 1 UID: 0 PID: 3037 Comm: syz.2.16 Not tainted 6.14.0-rc2-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024

Call Trace:

<TASK>

__dump_stack lib/dump_stack.c:94 [inline]

dump_stack_lvl+0x201/0x300 lib/dump_stack.c:120

ubsan_epilogue lib/ubsan.c:231 [inline]

__ubsan_handle_out_of_bounds+0xf5/0x120 lib/ubsan.c:429

sfq_link net/sched/sch_sfq.c:203 [inline]

sfq_dec+0x53c/0x610 net/sched/sch_sfq.c:231

sfq_dequeue+0x34e/0x8c0 net/sched/sch_sfq.c:493

sfq_reset+0x17/0x60 net/sched/sch_sfq.c:518

qdisc_reset+0x12e/0x600 net/sched/sch_generic.c:1035

tbf_reset+0x41/0x110 net/sched/sch_tbf.c:339

qdisc_reset+0x12e/0x600 net/sched/sch_generic.c:1035

dev_reset_queue+0x100/0x1b0 net/sched/sch_generic.c:1311

netdev_for_each_tx_queue include/linux/netdevice.h:2590 [inline]

dev_deactivate_many+0x7e5/0xe70 net/sched/sch_generic.c:1375