CVE-2021-47299 in Linux
Summary
by MITRE • 05/21/2024
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---
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability described in CVE-2021-47299 represents a critical use-after-free condition within the Linux kernel's XDP (eXpress Data Path) subsystem, specifically affecting the bpf_xdp_link_release function. This flaw occurs during the dynamic attachment and detachment of XDP programs to network devices, creating a race condition between device reference management and BPF link cleanup operations. The issue manifests when a network device undergoes the process of being unregistered while simultaneously having an XDP link associated with it, leading to memory access violations that can result in system crashes or potential privilege escalation.
The technical flaw stems from improper synchronization between device reference counting and XDP link management within the kernel's networking subsystem. During the sequence where dev_get_by_index() retrieves a network device reference followed by dev_xdp_attach_link(), the kernel's locking mechanisms fail to prevent concurrent device unregistration. When dev_xdp_uninstall() is invoked during the unregister_netdevice_many() process, it removes the XDP attachment but does not properly handle the case where the link structure still maintains a reference to the already-released device. This creates a dangling pointer scenario where bpf_xdp_link_release attempts to access dev->dev_addr or related device fields after the device memory has been freed, triggering a kernel memory safety violation.
This vulnerability directly maps to CWE-416, which defines use-after-free conditions in software systems, and aligns with ATT&CK technique T1068, which involves exploiting local privilege escalation through kernel vulnerabilities. The operational impact of this flaw extends beyond simple system crashes, as it can be exploited to achieve privilege escalation or denial of service attacks against systems running affected kernel versions. The race condition occurs in a high-privilege kernel context where malicious actors could potentially craft specific network operations to trigger the vulnerable code path, leading to system instability or unauthorized access to kernel memory spaces.
Mitigation strategies for this vulnerability include applying the official kernel patch that resolves the synchronization issue between device reference management and XDP link cleanup. System administrators should prioritize updating to kernel versions containing the fix, particularly those released after the vulnerability disclosure. Additionally, monitoring for kernel memory access violations and implementing proper kernel lockdown mechanisms can help detect and prevent exploitation attempts. Organizations should also consider implementing network segmentation and access controls to limit potential attack surfaces, while maintaining up-to-date security monitoring solutions to detect anomalous kernel behavior indicative of exploitation attempts. The patch addresses the core issue by ensuring proper reference counting and synchronization between device lifecycle management and BPF link operations, preventing the dangling pointer condition that leads to the use-after-free error.