CVE-2021-47557

CVE-2021-47557 is a medium-severity vulnerability in Linux Linux Kernel with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-476.

Key facts

Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_ets: don't peek at classes beyond 'nbands' when the number of DRR classes decreases, the round-robin active list can contain elements that have already been freed in ets_qdisc_change(). As a consequence, it's possible to see a NULL dereference crash, caused by the attempt to call cl->qdisc->ops->peek(cl->qdisc) when cl->qdisc is NULL: BUG: kernel NULL pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 1 PID: 910 Comm: mausezahn Not tainted 5.16.0-rc1+ #475 Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014 RIP: 0010:ets_qdisc_dequeue+0x129/0x2c0 [sch_ets] Code: c5 01 41 39 ad e4 02 00 00 0f 87 18 ff ff ff 49 8b 85 c0 02 00 00 49 39 c4 0f 84 ba 00 00 00 49 8b ad c0 02 00 00 48 8b 7d 10 <48> 8b 47 18 48 8b 40 38 0f ae e8 ff d0 48 89 c3 48 85 c0 0f 84 9d RSP: 0000:ffffbb36c0b5fdd8 EFLAGS: 00010287 RAX: ffff956678efed30 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000002 RSI: ffffffff9b938dc9 RDI: 0000000000000000 RBP: ffff956678efed30 R08: e2f3207fe360129c R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000001 R12: ffff956678efeac0 R13: ffff956678efe800 R14: ffff956611545000 R15: ffff95667ac8f100 FS: 00007f2aa9120740(0000) GS:ffff95667b800000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000018 CR3: 000000011070c000 CR4: 0000000000350ee0 Call Trace: <TASK> qdisc_peek_dequeued+0x29/0x70 [sch_ets] tbf_dequeue+0x22/0x260 [sch_tbf] __qdisc_run+0x7f/0x630 net_tx_action+0x290/0x4c0 __do_softirq+0xee/0x4f8 irq_exit_rcu+0xf4/0x130 sysvec_apic_timer_interrupt+0x52/0xc0 asm_sysvec_apic_timer_interrupt+0x12/0x20 RIP: 0033:0x7f2aa7fc9ad4 Code: b9 ff ff 48 8b 54 24 18 48 83 c4 08 48 89 ee 48 89 df 5b 5d e9 ed fc ff ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa <53> 48 83 ec 10 48 8b 05 10 64 33 00 48 8b 00 48 85 c0 0f 85 84 00 RSP: 002b:00007ffe5d33fab8 EFLAGS: 00000202 RAX: 0000000000000002 RBX: 0000561f72c31460 RCX: 0000561f72c31720 RDX: 0000000000000002 RSI: 0000561f72c31722 RDI: 0000561f72c31720 RBP: 000000000000002a R08: 00007ffe5d33fa40 R09: 0000000000000014 R10: 0000000000000000 R11: 0000000000000246 R12: 0000561f7187e380 R13: 0000000000000000 R14: 0000000000000000 R15: 0000561f72c31460 </TASK> Modules linked in: sch_ets sch_tbf dummy rfkill iTCO_wdt intel_rapl_msr iTCO_vendor_support intel_rapl_common joydev virtio_balloon lpc_ich i2c_i801 i2c_smbus pcspkr ip_tables xfs libcrc32c crct10dif_pclmul crc32_pclmul crc32c_intel ahci libahci ghash_clmulni_intel serio_raw libata virtio_blk virtio_console virtio_net net_failover failover sunrpc dm_mirror dm_region_hash dm_log dm_mod CR2: 0000000000000018 Ensuring that 'alist' was never zeroed [1] was not sufficient, we need to remove from the active list those elements that are no more SP nor DRR. [1] https://lore.kernel.org/netdev/60d274838bf09777f0371253416e8af71360bc08.1633609148.git.dcaratti@redhat.com/ v3: fix race between ets_qdisc_change() and ets_qdisc_dequeue() delisting DRR classes beyond 'nbands' in ets_qdisc_change() with the qdisc lock acquired, thanks to Cong Wang. v2: when a NULL qdisc is found in the DRR active list, try to dequeue skb from the next list item.

Frequently asked questions

What is CVE-2021-47557?
In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_ets: don't peek at classes beyond 'nbands' when the number of DRR classes decreases, the round-robin active list can contain elements that have already been freed in ets_qdisc_change(). As a consequence, it's possible to see a NULL dereference crash, caused by the attempt to call cl->qdisc->ops->peek(cl->qdisc) when cl->qdisc is NULL: BUG: kernel NULL pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 1 PID: 910 Comm: mausezahn Not tainted 5.16.0-rc1+ #475 Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014 RIP: 0010:ets_qdisc_dequeue+0x129/0x2c0 [sch_ets] Code: c5 01 41 39 ad e4 02 00 00 0f 87 18 ff ff ff 49 8b 85 c0 02 00 00 49 39 c4 0f 84 ba 00 00 00 49 8b ad c0 02 00 00 48 8b 7d 10 <48> 8b 47 18 48 8b 40 38 0f ae e8 ff d0 48 89 c3 48 85 c0 0f 84 9d RSP: 0000:ffffbb36c0b5fdd8 EFLAGS: 00010287 RAX: ffff956678efed30 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000002 RSI: ffffffff9b938dc9 RDI: 0000000000000000 RBP: ffff956678efed30 R08: e2f3207fe360129c R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000001 R12: ffff956678efeac0 R13: ffff956678efe800 R14: ffff956611545000 R15: ffff95667ac8f100 FS: 00007f2aa9120740(0000) GS:ffff95667b800000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000018 CR3: 000000011070c000 CR4: 0000000000350ee0 Call Trace: <TASK> qdisc_peek_dequeued+0x29/0x70 [sch_ets] tbf_dequeue+0x22/0x260 [sch_tbf] __qdisc_run+0x7f/0x630 net_tx_action+0x290/0x4c0 __do_softirq+0xee/0x4f8 irq_exit_rcu+0xf4/0x130 sysvec_apic_timer_interrupt+0x52/0xc0 asm_sysvec_apic_timer_interrupt+0x12/0x20 RIP: 0033:0x7f2aa7fc9ad4 Code: b9 ff ff 48 8b 54 24 18 48 83 c4 08 48 89 ee 48 89 df 5b 5d e9 ed fc ff ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa <53> 48 83 ec 10 48 8b 05 10 64 33 00 48 8b 00 48 85 c0 0f 85 84 00 RSP: 002b:00007ffe5d33fab8 EFLAGS: 00000202 RAX: 0000000000000002 RBX: 0000561f72c31460 RCX: 0000561f72c31720 RDX: 0000000000000002 RSI: 0000561f72c31722 RDI: 0000561f72c31720 RBP: 000000000000002a R08: 00007ffe5d33fa40 R09: 0000000000000014 R10: 0000000000000000 R11: 0000000000000246 R12: 0000561f7187e380 R13: 0000000000000000 R14: 0000000000000000 R15: 0000561f72c31460 </TASK> Modules linked in: sch_ets sch_tbf dummy rfkill iTCO_wdt intel_rapl_msr iTCO_vendor_support intel_rapl_common joydev virtio_balloon lpc_ich i2c_i801 i2c_smbus pcspkr ip_tables xfs libcrc32c crct10dif_pclmul crc32_pclmul crc32c_intel ahci libahci ghash_clmulni_intel serio_raw libata virtio_blk virtio_console virtio_net net_failover failover sunrpc dm_mirror dm_region_hash dm_log dm_mod CR2: 0000000000000018 Ensuring that 'alist' was never zeroed [1] was not sufficient, we need to remove from the active list those elements that are no more SP nor DRR. [1] https://lore.kernel.org/netdev/60d274838bf09777f0371253416e8af71360bc08.1633609148.git.dcaratti@redhat.com/ v3: fix race between ets_qdisc_change() and ets_qdisc_dequeue() delisting DRR classes beyond 'nbands' in ets_qdisc_change() with the qdisc lock acquired, thanks to Cong Wang. v2: when a NULL qdisc is found in the DRR active list, try to dequeue skb from the next list item.
How severe is CVE-2021-47557?
CVE-2021-47557 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-47557 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (15th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-47557?
CVE-2021-47557 primarily affects Linux Linux Kernel. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-47557?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2021-47557 have an EU (EUVD) identifier?
Yes. CVE-2021-47557 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-34559.
When was CVE-2021-47557 published?
CVE-2021-47557 was published on 2024-05-24 and last updated on 2026-06-17.

References

Affected products (3)

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