# CVE-2021-47451: linux: In the Linux kernel, the following vulnerability has been resolved:  netfilter: xt_IDLETIMER: fix panic that occurs w...

CVE-2021-47451 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47451, released May 22, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47451
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0024
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 22, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  netfilter: xt_IDLETIMER: fix panic that occurs when timer_type has garbage value  Currently, when the rule related to IDLETIMER is added, idletimer_tg timer structure is initialized by kmalloc on executing idletimer_tg_create function. However, in this process timer->timer_type is not defined to a specific value. Thus, timer->timer_type has garbage value and it occurs kernel panic. So, this commit fixes the panic by initializing timer->timer_type using kzalloc instead of kmalloc.  Test commands:     # iptables -A OUTPUT -j IDLETIMER --timeout 1 --label test     $ cat /sys/class/xt_idletimer/timers/test       Killed  Splat looks like:     BUG: KASAN: user-memory-access in alarm_expires_remaining+0x49/0x70     Read of size 8 at addr 0000002e8c7bc4c8 by task cat/917     CPU: 12 PID: 917 Comm: cat Not tainted 5.14.0+ #3 79940a339f71eb14fc81aee1757a20d5bf13eb0e     Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014     Call Trace:      dump_stack_lvl+0x6e/0x9c      kasan_report.cold+0x112/0x117      ? alarm_expires_remaining+0x49/0x70      __asan_load8+0x86/0xb0      alarm_expires_remaining+0x49/0x70      idletimer_tg_show+0xe5/0x19b [xt_IDLETIMER 11219304af9316a21bee5ba9d58f76a6b9bccc6d]      dev_attr_show+0x3c/0x60      sysfs_kf_seq_show+0x11d/0x1f0      ? device_remove_bin_file+0x20/0x20      kernfs_seq_show+0xa4/0xb0      seq_read_iter+0x29c/0x750      kernfs_fop_read_iter+0x25a/0x2c0      ? __fsnotify_parent+0x3d1/0x570      ? iov_iter_init+0x70/0x90      new_sync_read+0x2a7/0x3d0      ? __x64_sys_llseek+0x230/0x230      ? rw_verify_area+0x81/0x150      vfs_read+0x17b/0x240      ksys_read+0xd9/0x180      ? vfs_write+0x460/0x460      ? do_syscall_64+0x16/0xc0      ? lockdep_hardirqs_on+0x79/0x120      __x64_sys_read+0x43/0x50      do_syscall_64+0x3b/0xc0      entry_SYSCALL_64_after_hwframe+0x44/0xae     RIP: 0033:0x7f0cdc819142     Code: c0 e9 c2 fe ff ff 50 48 8d 3d 3a ca 0a 00 e8 f5 19 02 00 0f 1f 44 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 0f 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 48 83 ec 28 48 89 54 24     RSP: 002b:00007fff28eee5b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000     RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007f0cdc819142     RDX: 0000000000020000 RSI: 00007f0cdc032000 RDI: 0000000000000003     RBP: 00007f0cdc032000 R08: 00007f0cdc031010 R09: 0000000000000000     R10: 0000000000000022 R11: 0000000000000246 R12: 00005607e9ee31f0     R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.14.16-1 | [DEBIAN-CVE-2021-47451](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47451.md) | May 22, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.14.16-1 | [DEBIAN-CVE-2021-47451](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47451.md) | May 22, 2024 |
| Linux | linux Debian 14 | 5.14.16-1 | [DEBIAN-CVE-2021-47451](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47451.md) | May 22, 2024 |

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