Linux Distros 未修补的漏洞：CVE-2021-47128
medium Nessus 插件 ID 247937
语言：
简介
Linux/Unix 主机上安装的一个或多个程序包存在漏洞，但供应商表示不会修补此漏洞。描述
Linux/Unix 主机中安装的一个或多个程序包受到一个漏洞影响，而供应商没有提供补丁程序。- 已修复 Linux 内核中的下列漏洞：bpf, lockdown, audit: Fix buggy SELinux lockdown permission checks Commit 59438b46471a (security,lockdown,selinux: implement SELinux lockdown) added an implementation of the locked_down LSM hook to SELinux, with the aim to restrict which domains are allowed to perform operations that would breach lockdown. This is indirectly also getting audit subsystem involved to report events. The latter is problematic, as reported by Ondrej and Serhei, since it can bring down the whole system via audit: 1) The audit events that are triggered due to calls to security_locked_down() can OOM kill a machine, see below details [0]. 2) It also seems to be causing a deadlock via avc_has_perm()/slow_avc_audit() when trying to wake up kauditd, for example, when using trace_sched_switch() tracepoint, see details in [1]. Triggering this was not via some hypothetical corner case, but with existing tools like runqlat & runqslower from bcc, for example, which make use of this tracepoint. Rough call sequence goes like: rq_lock(rq) -> -------------------------+ trace_sched_switch()
-> | bpf_prog_xyz() -> +-> deadlock selinux_lockdown() -> | audit_log_end() -> | wake_up_interruptible()
-> | try_to_wake_up() -> | rq_lock(rq) --------------+ What's worse is that the intention of 59438b46471a to further restrict lockdown settings for specific applications in respect to the global lockdown policy is completely broken for BPF. The SELinux policy rule for the current lockdown check looks something like this: allow <who> <who> : lockdown { <reason> }; However, this doesn't match with the 'current' task where the security_locked_down() is executed, example: httpd does a syscall. There is a tracing program attached to the syscall which triggers a BPF program to run, which ends up doing a bpf_probe_read_kernel{,_str}() helper call. The selinux_lockdown() hook does the permission check against 'current', that is, httpd in this example. httpd has literally zero relation to this tracing program, and it would be nonsensical having to write an SELinux policy rule against httpd to let the tracing helper pass. The policy in this case needs to be against the entity that is installing the BPF program. For example, if bpftrace would generate a histogram of syscall counts by user space application: bpftrace -e 'tracepoint:raw_syscalls:sys_enter { @[comm] = count(); }' bpftrace would then go and generate a BPF program from this internally. One way of doing it [for the sake of the example] could be to call bpf_get_current_task() helper and then access current->comm via one of bpf_probe_read_kernel{,_str}() helpers. So the program itself has nothing to do with httpd or any other random app doing a syscall here.
The BPF program _explicitly initiated_ the lockdown check. The allow/deny policy belongs in the context of bpftrace: meaning, you want to grant bpftrace access to use these helpers, but other tracers on the system like my_random_tracer _not_. Therefore fix all three issues at the same time by taking a completely different approach for the security_locked_down() hook, that is, move the check into the program verification phase where we actually retrieve the BPF func proto. This also reliably gets the task (current) that is trying to install the BPF tracing program, e.g. bpftrace/bcc/perf/systemtap/etc, and it also fixes the OOM since we're moving this out of the BPF helper's fast-path which can be called several millions of times per second. The check is then also in line with other security_locked_down() hooks in the system where the enforcement is performed at open/load time, for example, open_kcore() for /proc/kcore access or module_sig_check() for module signatures just to pick f ---truncated--- (CVE-2021-47128)
请注意，Nessus 依赖供应商报告的程序包是否存在进行判断。
解决方案
目前尚未有任何已知的解决方案。另见
插件详情
严重性: Medium
ID: 247937
文件名: unpatched_CVE_2021_47128.nasl
版本: 1.1
类型: local
代理: unix
系列: Misc.
发布时间: 2025/8/11
最近更新时间: 2025/8/11
支持的传感器: Frictionless Assessment AWS, Frictionless Assessment Azure, Frictionless Assessment Agent, Nessus Agent, Agentless Assessment, Nessus
风险信息
VPR
风险因素: Medium
分数: 4.4
CVSS v2
风险因素: Medium
基本分数: 6.2
时间分数: 4.6
矢量: CVSS2#AV:L/AC:L/Au:S/C:N/I:C/A:C
CVSS 分数来源: CVE-2021-47128
CVSS v3
风险因素: Medium
基本分数: 5.5
时间分数: 4.8
矢量: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
时间矢量: CVSS:3.0/E:U/RL:O/RC:C
漏洞信息
CPE: p-cpe:/a:canonical:ubuntu_linux:linux-hwe, p-cpe:/a:canonical:ubuntu_linux:linux-intel-5.13, cpe:/o:canonical:ubuntu_linux:16.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:linux-oracle-5.3, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-edge, cpe:/o:canonical:ubuntu_linux:22.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:linux-lowlatency-hwe-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-oracle-5.0, p-cpe:/a:canonical:ubuntu_linux:linux-oracle-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-lowlatency-hwe-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-gke-5.15, p-cpe:/a:canonical:ubuntu_linux:linux-oem-5.17, p-cpe:/a:canonical:ubuntu_linux:linux-gcp, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-azure-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-riscv-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-riscv, p-cpe:/a:canonical:ubuntu_linux:linux-gke, p-cpe:/a:canonical:ubuntu_linux:linux-riscv-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-starfive-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-5.3, p-cpe:/a:canonical:ubuntu_linux:linux-azure, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.3, p-cpe:/a:canonical:ubuntu_linux:linux-azure-edge, p-cpe:/a:canonical:ubuntu_linux:linux-azure-fde, p-cpe:/a:canonical:ubuntu_linux:linux-aws-6.2, cpe:/o:canonical:ubuntu_linux:18.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:linux-gkeop-5.4, p-cpe:/a:canonical:ubuntu_linux:linux-oem, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-allwinner-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-nvidia-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.0, p-cpe:/a:canonical:ubuntu_linux:linux-oem-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-oem-6.0, p-cpe:/a:canonical:ubuntu_linux:linux-azure-5.3, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-azure-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-azure-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-oem-5.10, p-cpe:/a:canonical:ubuntu_linux:linux-raspi2, p-cpe:/a:canonical:ubuntu_linux:linux-gke-5.4, p-cpe:/a:canonical:ubuntu_linux:linux-azure-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-gke-4.15, p-cpe:/a:canonical:ubuntu_linux:linux-oracle-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-riscv-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-starfive-6.2, cpe:/o:canonical:ubuntu_linux:20.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:linux-oem-5.14, p-cpe:/a:canonical:ubuntu_linux:linux-azure-fde-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-azure-fde-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-oem-5.6, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-oracle-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-oem-6.1, p-cpe:/a:canonical:ubuntu_linux:linux-azure-5.13
必需的 KB 项: Host/local_checks_enabled, Host/cpu, global_settings/vendor_unpatched, Host/OS/identifier
易利用性: No known exploits are available
漏洞发布日期: 2022/1/28
参考资料信息
CVE: CVE-2021-47128