CVE-2021-47299: Vulnerability in Linux Linux

Severity: highType: vulnerabilityCVE-2021-47299

In the Linux kernel, the following vulnerability has been resolved: xdp, net: Fix use-after-free in bpf_xdp_link_release The problem occurs between dev_get_by_index() and dev_xdp_attach_link(). At this point, dev_xdp_uninstall() is called. Then xdp link will not be detached automatically when dev is released. But link->dev already points to dev, when xdp link is released, dev will still be accessed, but dev has been released. dev_get_by_index() | link->dev = dev | | rtnl_lock() | unregister_netdevice_many() | dev_xdp_uninstall() | rtnl_unlock() rtnl_lock(); | dev_xdp_attach_link() | rtnl_unlock(); | | netdev_run_todo() // dev released bpf_xdp_link_release() | /* access dev. | use-after-free */ | [ 45.966867] BUG: KASAN: use-after-free in bpf_xdp_link_release+0x3b8/0x3d0 [ 45.967619] Read of size 8 at addr ffff00000f9980c8 by task a.out/732 [ 45.968297] [ 45.968502] CPU: 1 PID: 732 Comm: a.out Not tainted 5.13.0+ #22 [ 45.969222] Hardware name: linux,dummy-virt (DT) [ 45.969795] Call trace: [ 45.970106] dump_backtrace+0x0/0x4c8 [ 45.970564] show_stack+0x30/0x40 [ 45.970981] dump_stack_lvl+0x120/0x18c [ 45.971470] print_address_description.constprop.0+0x74/0x30c [ 45.972182] kasan_report+0x1e8/0x200 [ 45.972659] __asan_report_load8_noabort+0x2c/0x50 [ 45.973273] bpf_xdp_link_release+0x3b8/0x3d0 [ 45.973834] bpf_link_free+0xd0/0x188 [ 45.974315] bpf_link_put+0x1d0/0x218 [ 45.974790] bpf_link_release+0x3c/0x58 [ 45.975291] __fput+0x20c/0x7e8 [ 45.975706] ____fput+0x24/0x30 [ 45.976117] task_work_run+0x104/0x258 [ 45.976609] do_notify_resume+0x894/0xaf8 [ 45.977121] work_pending+0xc/0x328 [ 45.977575] [ 45.977775] The buggy address belongs to the page: [ 45.978369] page:fffffc00003e6600 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x4f998 [ 45.979522] flags: 0x7fffe0000000000(node=0|zone=0|lastcpupid=0x3ffff) [ 45.980349] raw: 07fffe0000000000 fffffc00003e6708 ffff0000dac3c010 0000000000000000 [ 45.981309] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 [ 45.982259] page dumped because: kasan: bad access detected [ 45.982948] [ 45.983153] Memory state around the buggy address: [ 45.983753] ffff00000f997f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 45.984645] ffff00000f998000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 45.985533] >ffff00000f998080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 45.986419] ^ [ 45.987112] ffff00000f998100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 45.988006] ffff00000f998180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 45.988895] ================================================================== [ 45.989773] Disabling lock debugging due to kernel taint [ 45.990552] Kernel panic - not syncing: panic_on_warn set ... [ 45.991166] CPU: 1 PID: 732 Comm: a.out Tainted: G B 5.13.0+ #22 [ 45.991929] Hardware name: linux,dummy-virt (DT) [ 45.992448] Call trace: [ 45.992753] dump_backtrace+0x0/0x4c8 [ 45.993208] show_stack+0x30/0x40 [ 45.993627] dump_stack_lvl+0x120/0x18c [ 45.994113] dump_stack+0x1c/0x34 [ 45.994530] panic+0x3a4/0x7d8 [ 45.994930] end_report+0x194/0x198 [ 45.995380] kasan_report+0x134/0x200 [ 45.995850] __asan_report_load8_noabort+0x2c/0x50 [ 45.996453] bpf_xdp_link_release+0x3b8/0x3d0 [ 45.997007] bpf_link_free+0xd0/0x188 [ 45.997474] bpf_link_put+0x1d0/0x218 [ 45.997942] bpf_link_release+0x3c/0x58 [ 45.998429] __fput+0x20c/0x7e8 [ 45.998833] ____fput+0x24/0x30 [ 45.999247] task_work_run+0x104/0x258 [ 45.999731] do_notify_resume+0x894/0xaf8 [ 46.000236] work_pending ---truncated---

AI Analysis

Technical Summary

CVE-2021-47299 is a use-after-free vulnerability identified in the Linux kernel's eXpress Data Path (XDP) networking subsystem, specifically within the bpf_xdp_link_release function. The flaw arises due to improper handling of network device references during the attachment and detachment of XDP links. The sequence involves dev_get_by_index() obtaining a reference to a network device, which is then assigned to link->dev. However, during the process, dev_xdp_uninstall() is called, which does not automatically detach the XDP link when the network device is released. Consequently, when bpf_xdp_link_release() attempts to access the device through link->dev, it may reference a device that has already been freed, leading to a use-after-free condition. This vulnerability can cause kernel memory corruption, crashes, and potentially kernel panics, as evidenced by the provided kernel address sanitizer (KASAN) logs showing invalid memory access and subsequent panic. The vulnerability affects Linux kernel versions containing the specified commit hashes and is rooted in the race condition between device release and XDP link detachment. No public exploits are currently known, and no CVSS score has been assigned yet.

Potential Impact

For European organizations, this vulnerability poses significant risks especially for those relying on Linux-based infrastructure for networking, cloud services, and edge computing. Exploitation could lead to denial of service (DoS) through kernel crashes or panics, disrupting critical services and network operations. In environments where Linux kernels are used in data centers, telecommunications, or industrial control systems, this could result in operational downtime and potential loss of availability. Although direct privilege escalation or remote code execution is not explicitly documented, the kernel memory corruption could be leveraged in complex attack chains. The vulnerability is particularly concerning for organizations using XDP for high-performance packet processing, such as ISPs, cloud providers, and enterprises with advanced networking setups. Given the widespread use of Linux in European public and private sectors, the impact could be broad, affecting service continuity and requiring urgent patching to maintain system integrity and availability.

Mitigation Recommendations

Organizations should promptly update their Linux kernels to versions where this vulnerability is patched. Since no patch links are provided in the data, monitoring official Linux kernel repositories and vendor advisories (e.g., from distributions like Debian, Ubuntu, Red Hat, SUSE) is critical to obtain and apply the fix. Additionally, administrators should audit the use of XDP in their environments and consider temporarily disabling XDP features if immediate patching is not feasible, to reduce exposure. Implementing kernel lockdown mechanisms and restricting unprivileged BPF/XDP usage can further mitigate risk. Monitoring kernel logs for unusual crashes or KASAN reports can help detect exploitation attempts. Network segmentation and limiting access to systems running vulnerable kernels will reduce the attack surface. Finally, integrating vulnerability management processes to track Linux kernel updates and applying them in a timely manner is essential.