CVE-2021-47418 net_sched: fix NULL deref in fifo_set_limit()

2024-05-2115:04:07

Linux

www.cve.org

linux kernel

vulnerability

null dereference

fifo_set_limit

syzbot

unshare

tbf limit

burst rate

pfifo_fast

bug

google compute engine

bios

rip

cpu

pid

comm

hardware name

call trace

kernel null pointer

netlink

syscall

6.2 Medium

AI Score

Confidence

Low

0.0004 Low

EPSS

Percentile

13.1%

JSON

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

net_sched: fix NULL deref in fifo_set_limit()

syzbot reported another NULL deref in fifo_set_limit() [1]

I could repro the issue with :

unshare -n
tc qd add dev lo root handle 1:0 tbf limit 200000 burst 70000 rate 100Mbit
tc qd replace dev lo parent 1:0 pfifo_fast
tc qd change dev lo root handle 1:0 tbf limit 300000 burst 70000 rate 100Mbit

pfifo_fast does not have a change() operation.
Make fifo_set_limit() more robust about this.

[1]
BUG: kernel NULL pointer dereference, address: 0000000000000000
PGD 1cf99067 P4D 1cf99067 PUD 7ca49067 PMD 0
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 14443 Comm: syz-executor959 Not tainted 5.15.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:0x0
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
RSP: 0018:ffffc9000e2f7310 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffffffff8d6ecc00 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff888024c27910 RDI: ffff888071e34000
RBP: ffff888071e34000 R08: 0000000000000001 R09: ffffffff8fcfb947
R10: 0000000000000001 R11: 0000000000000000 R12: ffff888024c27910
R13: ffff888071e34018 R14: 0000000000000000 R15: ffff88801ef74800
FS: 00007f321d897700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000000722c3000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
fifo_set_limit net/sched/sch_fifo.c:242 [inline]
fifo_set_limit+0x198/0x210 net/sched/sch_fifo.c:227
tbf_change+0x6ec/0x16d0 net/sched/sch_tbf.c:418
qdisc_change net/sched/sch_api.c:1332 [inline]
tc_modify_qdisc+0xd9a/0x1a60 net/sched/sch_api.c:1634
rtnetlink_rcv_msg+0x413/0xb80 net/core/rtnetlink.c:5572
netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2504
netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1340
netlink_sendmsg+0x86d/0xdb0 net/netlink/af_netlink.c:1929
sock_sendmsg_nosec net/socket.c:704 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:724
____sys_sendmsg+0x6e8/0x810 net/socket.c:2409
___sys_sendmsg+0xf3/0x170 net/socket.c:2463
__sys_sendmsg+0xe5/0x1b0 net/socket.c:2492
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "net/sched/sch_fifo.c"
    ],
    "versions": [
      {
        "version": "fb0305ce1b03",
        "lessThan": "0dd7ddc462b9",
        "status": "affected",
        "versionType": "git"
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  },
  {
    "product": "Linux",
    "vendor": "Linux",
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    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "net/sched/sch_fifo.c"
    ],
    "versions": [
      {
        "version": "2.6.27",
        "status": "affected"
      },
      {
        "version": "0",
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        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.4.289",
        "lessThanOrEqual": "4.4.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.9.287",
        "lessThanOrEqual": "4.9.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.14.251",
        "lessThanOrEqual": "4.14.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.19.211",
        "lessThanOrEqual": "4.19.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.4.153",
        "lessThanOrEqual": "5.4.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.73",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.14.12",
        "lessThanOrEqual": "5.14.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.15",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]