# CVE-2021-47274: linux: In the Linux kernel, the following vulnerability has been resolved:  tracing: Correct the length check which causes m...

CVE-2021-47274 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47274, released May 21, 2024. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2021-47274
- Priority: High
- CVSS: 7.8 (high)
- EPSS: 0.0075
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 21, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  tracing: Correct the length check which causes memory corruption  We've suffered from severe kernel crashes due to memory corruption on our production environment, like,  Call Trace: [1640542.554277] general protection fault: 0000 [#1] SMP PTI [1640542.554856] CPU: 17 PID: 26996 Comm: python Kdump: loaded Tainted:G [1640542.556629] RIP: 0010:kmem_cache_alloc+0x90/0x190 [1640542.559074] RSP: 0018:ffffb16faa597df8 EFLAGS: 00010286 [1640542.559587] RAX: 0000000000000000 RBX: 0000000000400200 RCX: 0000000006e931bf [1640542.560323] RDX: 0000000006e931be RSI: 0000000000400200 RDI: ffff9a45ff004300 [1640542.560996] RBP: 0000000000400200 R08: 0000000000023420 R09: 0000000000000000 [1640542.561670] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff9a20608d [1640542.562366] R13: ffff9a45ff004300 R14: ffff9a45ff004300 R15: 696c662f65636976 [1640542.563128] FS:  00007f45d7c6f740(0000) GS:ffff9a45ff840000(0000) knlGS:0000000000000000 [1640542.563937] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [1640542.564557] CR2: 00007f45d71311a0 CR3: 000000189d63e004 CR4: 00000000003606e0 [1640542.565279] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [1640542.566069] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [1640542.566742] Call Trace: [1640542.567009]  anon_vma_clone+0x5d/0x170 [1640542.567417]  __split_vma+0x91/0x1a0 [1640542.567777]  do_munmap+0x2c6/0x320 [1640542.568128]  vm_munmap+0x54/0x70 [1640542.569990]  __x64_sys_munmap+0x22/0x30 [1640542.572005]  do_syscall_64+0x5b/0x1b0 [1640542.573724]  entry_SYSCALL_64_after_hwframe+0x44/0xa9 [1640542.575642] RIP: 0033:0x7f45d6e61e27  James Wang has reproduced it stably on the latest 4.19 LTS. After some debugging, we finally proved that it's due to ftrace buffer out-of-bound access using a debug tool as follows: [   86.775200] BUG: Out-of-bounds write at addr 0xffff88aefe8b7000 [   86.780806]  no_context+0xdf/0x3c0 [   86.784327]  __do_page_fault+0x252/0x470 [   86.788367]  do_page_fault+0x32/0x140 [   86.792145]  page_fault+0x1e/0x30 [   86.795576]  strncpy_from_unsafe+0x66/0xb0 [   86.799789]  fetch_memory_string+0x25/0x40 [   86.804002]  fetch_deref_string+0x51/0x60 [   86.808134]  kprobe_trace_func+0x32d/0x3a0 [   86.812347]  kprobe_dispatcher+0x45/0x50 [   86.816385]  kprobe_ftrace_handler+0x90/0xf0 [   86.820779]  ftrace_ops_assist_func+0xa1/0x140 [   86.825340]  0xffffffffc00750bf [   86.828603]  do_sys_open+0x5/0x1f0 [   86.832124]  do_syscall_64+0x5b/0x1b0 [   86.835900]  entry_SYSCALL_64_after_hwframe+0x44/0xa9  commit b220c049d519 ("tracing: Check length before giving out the filter buffer") adds length check to protect trace data overflow introduced in 0fc1b09ff1ff, seems that this fix can't prevent overflow entirely, the length check should also take the sizeof entry->array[0] into account, since this array[0] is filled the length of trace data and occupy addtional space and risk overflow.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.10.46-1 | [DEBIAN-CVE-2021-47274](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47274.md) | May 21, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.10.46-1 | [DEBIAN-CVE-2021-47274](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47274.md) | May 21, 2024 |
| Linux | linux Debian 14 | 5.10.46-1 | [DEBIAN-CVE-2021-47274](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47274.md) | May 21, 2024 |

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