github - ghsa-fp67-w4xm-4hj6

GHSA-FP67-W4XM-4HJ6

Vulnerability from github – Published: 2024-06-19 15:30 – Updated: 2024-10-31 15:30

Details

In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix kernel address leakage in atomic cmpxchg's r0 aux reg

The implementation of BPF_CMPXCHG on a high level has the following parameters:

.-[old-val] .-[new-val] BPF_R0 = cmpxchg{32,64}(DST_REG + insn->off, BPF_R0, SRC_REG) -[mem-loc]-[old-val]

Given a BPF insn can only have two registers (dst, src), the R0 is fixed and used as an auxilliary register for input (old value) as well as output (returning old value from memory location). While the verifier performs a number of safety checks, it misses to reject unprivileged programs where R0 contains a pointer as old value.

Through brute-forcing it takes about ~16sec on my machine to leak a kernel pointer with BPF_CMPXCHG. The PoC is basically probing for kernel addresses by storing the guessed address into the map slot as a scalar, and using the map value pointer as R0 while SRC_REG has a canary value to detect a matching address.

Fix it by checking R0 for pointers, and reject if that's the case for unprivileged programs.

Severity ?

5.5 (Medium)


                  
                    CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

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{
  "affected": [],
  "aliases": [
    "CVE-2021-47607"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2024-06-19T15:15:55Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix kernel address leakage in atomic cmpxchg\u0027s r0 aux reg\n\nThe implementation of BPF_CMPXCHG on a high level has the following parameters:\n\n  .-[old-val]                                          .-[new-val]\n  BPF_R0 = cmpxchg{32,64}(DST_REG + insn-\u003eoff, BPF_R0, SRC_REG)\n                          `-[mem-loc]          `-[old-val]\n\nGiven a BPF insn can only have two registers (dst, src), the R0 is fixed and\nused as an auxilliary register for input (old value) as well as output (returning\nold value from memory location). While the verifier performs a number of safety\nchecks, it misses to reject unprivileged programs where R0 contains a pointer as\nold value.\n\nThrough brute-forcing it takes about ~16sec on my machine to leak a kernel pointer\nwith BPF_CMPXCHG. The PoC is basically probing for kernel addresses by storing the\nguessed address into the map slot as a scalar, and using the map value pointer as\nR0 while SRC_REG has a canary value to detect a matching address.\n\nFix it by checking R0 for pointers, and reject if that\u0027s the case for unprivileged\nprograms.",
  "id": "GHSA-fp67-w4xm-4hj6",
  "modified": "2024-10-31T15:30:58Z",
  "published": "2024-06-19T15:30:55Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-47607"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a82fe085f344ef20b452cd5f481010ff96b5c4cd"
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}

CVE-2021-47607 (GCVE-0-2021-47607)

Vulnerability from cvelistv5 – Published: 2024-06-19 14:54 – Updated: 2025-05-04 07:14

Summary

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix kernel address leakage in atomic cmpxchg's r0 aux reg The implementation of BPF_CMPXCHG on a high level has the following parameters: .-[old-val] .-[new-val] BPF_R0 = cmpxchg{32,64}(DST_REG + insn->off, BPF_R0, SRC_REG) `-[mem-loc] `-[old-val] Given a BPF insn can only have two registers (dst, src), the R0 is fixed and used as an auxilliary register for input (old value) as well as output (returning old value from memory location). While the verifier performs a number of safety checks, it misses to reject unprivileged programs where R0 contains a pointer as old value. Through brute-forcing it takes about ~16sec on my machine to leak a kernel pointer with BPF_CMPXCHG. The PoC is basically probing for kernel addresses by storing the guessed address into the map slot as a scalar, and using the map value pointer as R0 while SRC_REG has a canary value to detect a matching address. Fix it by checking R0 for pointers, and reject if that's the case for unprivileged programs.

Severity ?

No CVSS data available.

Assigner

Linux

References

URL

Tags

	https://git.kernel.org/stable/c/f87a6c160ecc8c7b4…
	https://git.kernel.org/stable/c/a82fe085f344ef20b…

Impacted products

Vendor

Product

Version

Linux

Affected: 5ffa25502b5ab3d639829a2d1e316cff7f59a41e , < f87a6c160ecc8c7b417d25f508d3f076fe346136 (git)
Affected: 5ffa25502b5ab3d639829a2d1e316cff7f59a41e , < a82fe085f344ef20b452cd5f481010ff96b5c4cd (git)

Linux

Affected: 5.12
Unaffected: 0 , < 5.12 (semver)
Unaffected: 5.15.11 , ≤ 5.15.* (semver)
Unaffected: 5.16 , ≤ * (original_commit_for_fix)

Show details on NVD website

JSON

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Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-FP67-W4XM-4HJ6

CVE-2021-47607 (GCVE-0-2021-47607)

Tags

Sightings

Nomenclature