Vulnerability CVE-2021-47175
Published: 2024-03-25

Description:
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.

 References:
https://git.kernel.org/stable/c/e6294c06e7c62ffdd5bf3df696d3a4fcbb753d3c
https://git.kernel.org/stable/c/7a1bdec12e43e29cc34a4394590337069d8812ce
https://git.kernel.org/stable/c/e70f7a11876a1a788ceadf75e9e5f7af2c868680
Copyright 2026, cxsecurity.com

 

Back to Top