CVE-2021-46936— net: fix use-after-free in tw_timer_handler
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I. Basic Information for CVE-2021-46936
Vulnerability Information
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Vulnerability Title
net: fix use-after-free in tw_timer_handler
Source: NVD (National Vulnerability Database)
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: net: fix use-after-free in tw_timer_handler A real world panic issue was found as follow in Linux 5.4. BUG: unable to handle page fault for address: ffffde49a863de28 PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0 RIP: 0010:tw_timer_handler+0x20/0x40 Call Trace: <IRQ> call_timer_fn+0x2b/0x120 run_timer_softirq+0x1ef/0x450 __do_softirq+0x10d/0x2b8 irq_exit+0xc7/0xd0 smp_apic_timer_interrupt+0x68/0x120 apic_timer_interrupt+0xf/0x20 This issue was also reported since 2017 in the thread [1], unfortunately, the issue was still can be reproduced after fixing DCCP. The ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net namespace is destroyed since tcp_sk_ops is registered befrore ipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops in the list of pernet_list. There will be a use-after-free on net->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net if there are some inflight time-wait timers. This bug is not introduced by commit f2bf415cfed7 ("mib: add net to NET_ADD_STATS_BH") since the net_statistics is a global variable instead of dynamic allocation and freeing. Actually, commit 61a7e26028b9 ("mib: put net statistics on struct net") introduces the bug since it put net statistics on struct net and free it when net namespace is destroyed. Moving init_ipv4_mibs() to the front of tcp_init() to fix this bug and replace pr_crit() with panic() since continuing is meaningless when init_ipv4_mibs() fails. [1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1
Source: NVD (National Vulnerability Database)
CVSS Information
N/A
Source: NVD (National Vulnerability Database)
Vulnerability Type
N/A
Source: NVD (National Vulnerability Database)
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel 存在安全漏洞，该漏洞源于 tw_timer_handler 中的释放后重用。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
II. Public POCs for CVE-2021-46936
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Same Patch Batch · Linux · 2024-02-27 · 67 CVEs total
| CVE-2021-46951 | tpm: efi: Use local variable for calculating final log size | |
| CVE-2021-46971 | perf/core: Fix unconditional security_locked_down() call | |
| CVE-2021-46970 | bus: mhi: pci_generic: Remove WQ_MEM_RECLAIM flag from state workqueue | |
| CVE-2021-46969 | bus: mhi: core: Fix invalid error returning in mhi_queue | |
| CVE-2021-46957 | riscv/kprobe: fix kernel panic when invoking sys_read traced by kprobe | |
| CVE-2021-46956 | virtiofs: fix memory leak in virtio_fs_probe() | |
| CVE-2021-46955 | openvswitch: fix stack OOB read while fragmenting IPv4 packets | |
| CVE-2021-46954 | net/sched: sch_frag: fix stack OOB read while fragmenting IPv4 packets | |
| CVE-2021-46953 | ACPI: GTDT: Don't corrupt interrupt mappings on watchdow probe failure | |
| CVE-2021-46952 | NFS: fs_context: validate UDP retrans to prevent shift out-of-bounds | |
| CVE-2021-46958 | btrfs: fix race between transaction aborts and fsyncs leading to use-after-free | |
| CVE-2021-46950 | md/raid1: properly indicate failure when ending a failed write request | |
| CVE-2021-46949 | sfc: farch: fix TX queue lookup in TX flush done handling | |
| CVE-2021-46948 | sfc: farch: fix TX queue lookup in TX event handling | |
| CVE-2021-46947 | sfc: adjust efx->xdp_tx_queue_count with the real number of initialized queues | |
| CVE-2021-46945 | ext4: always panic when errors=panic is specified | |
| CVE-2021-46944 | media: staging/intel-ipu3: Fix memory leak in imu_fmt | |
| CVE-2021-46943 | media: staging/intel-ipu3: Fix set_fmt error handling | |
| CVE-2021-46942 | io_uring: fix shared sqpoll cancellation hangs | |
| CVE-2021-46941 | usb: dwc3: core: Do core softreset when switch mode |
Showing top 20 of 67 CVEs. View all on vendor page → →
IV. Related Vulnerabilities
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Same vendor: Linux
- CVE-2026-43500
rxrpc: Also unshare DATA/RESPONSE packets when paged frags a - CVE-2026-43475
scsi: storvsc: Fix scheduling while atomic on PREEMPT_RT - CVE-2026-43474
fs: init flags_valid before calling vfs_fileattr_get - CVE-2026-43473
scsi: mpi3mr: Add NULL checks when resetting request and rep - CVE-2026-43472
unshare: fix unshare_fs() handling
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