CVE-2021-47175

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

net/sched: fq_pie: fix OOB access in the traffic path

the following script:

# tc qdisc add dev eth0 handle 0x1 root fq_pie flows 2

# tc qdisc add dev eth0 clsact

# tc filter add dev eth0 egress matchall action skbedit priority 0x10002

# ping 192.0.2.2 -I eth0 -c2 -w1 -q

produces the following splat:

BUG: KASAN: slab-out-of-bounds in fq_pie_qdisc_enqueue+0x1314/0x19d0 [sch_fq_pie]

Read of size 4 at addr ffff888171306924 by task ping/942

CPU: 3 PID: 942 Comm: ping Not tainted 5.12.0+ #441

Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014

Call Trace:

dump_stack+0x92/0xc1

print_address_description.constprop.7+0x1a/0x150

kasan_report.cold.13+0x7f/0x111

fq_pie_qdisc_enqueue+0x1314/0x19d0 [sch_fq_pie]

__dev_queue_xmit+0x1034/0x2b10

ip_finish_output2+0xc62/0x2120

__ip_finish_output+0x553/0xea0

ip_output+0x1ca/0x4d0

ip_send_skb+0x37/0xa0

raw_sendmsg+0x1c4b/0x2d00

sock_sendmsg+0xdb/0x110

__sys_sendto+0x1d7/0x2b0

__x64_sys_sendto+0xdd/0x1b0

do_syscall_64+0x3c/0x80

entry_SYSCALL_64_after_hwframe+0x44/0xae

RIP: 0033:0x7fe69735c3eb

Code: 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 f3 0f 1e fa 48 8d 05 75 42 2c 00 41 89 ca 8b 00 85 c0 75 14 b8 2c 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 75 c3 0f 1f 40 00 41 57 4d 89 c7 41 56 41 89

RSP: 002b:00007fff06d7fb38 EFLAGS: 00000246 ORIG_RAX: 000000000000002c

RAX: ffffffffffffffda RBX: 000055e961413700 RCX: 00007fe69735c3eb

RDX: 0000000000000040 RSI: 000055e961413700 RDI: 0000000000000003

RBP: 0000000000000040 R08: 000055e961410500 R09: 0000000000000010

R10: 0000000000000000 R11: 0000000000000246 R12: 00007fff06d81260

R13: 00007fff06d7fb40 R14: 00007fff06d7fc30 R15: 000055e96140f0a0

Allocated by task 917:

kasan_save_stack+0x19/0x40

__kasan_kmalloc+0x7f/0xa0

__kmalloc_node+0x139/0x280

fq_pie_init+0x555/0x8e8 [sch_fq_pie]

qdisc_create+0x407/0x11b0

tc_modify_qdisc+0x3c2/0x17e0

rtnetlink_rcv_msg+0x346/0x8e0

netlink_rcv_skb+0x120/0x380

netlink_unicast+0x439/0x630

netlink_sendmsg+0x719/0xbf0

sock_sendmsg+0xe2/0x110

____sys_sendmsg+0x5ba/0x890

___sys_sendmsg+0xe9/0x160

__sys_sendmsg+0xd3/0x170

do_syscall_64+0x3c/0x80

entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff888171306800

which belongs to the cache kmalloc-256 of size 256

The buggy address is located 36 bytes to the right of

256-byte region [ffff888171306800, ffff888171306900)

The buggy address belongs to the page:

page:00000000bcfb624e refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x171306

head:00000000bcfb624e order:1 compound_mapcount:0

flags: 0x17ffffc0010200(slab|head|node=0|zone=2|lastcpupid=0x1fffff)

raw: 0017ffffc0010200 dead000000000100 dead000000000122 ffff888100042b40

raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000

page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff888171306800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

ffff888171306880: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc

>ffff888171306900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

^

ffff888171306980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

ffff888171306a00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

fix fq_pie traffic path to avoid selecting 'q->flows + q->flows_cnt' as a

valid flow: it's an address beyond the allocated memory.