ghsa-vf64-qg5h-qxhf
Vulnerability from github
Published
2024-10-21 15:32
Modified
2024-12-14 21:31
Severity ?
7.1 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
Details

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

bpf: Fix helper writes to read-only maps

Lonial found an issue that despite user- and BPF-side frozen BPF map (like in case of .rodata), it was still possible to write into it from a BPF program side through specific helpers having ARG_PTR_TO_{LONG,INT} as arguments.

In check_func_arg() when the argument is as mentioned, the meta->raw_mode is never set. Later, check_helper_mem_access(), under the case of PTR_TO_MAP_VALUE as register base type, it assumes BPF_READ for the subsequent call to check_map_access_type() and given the BPF map is read-only it succeeds.

The helpers really need to be annotated as ARG_PTR_TO_{LONG,INT} | MEM_UNINIT when results are written into them as opposed to read out of them. The latter indicates that it's okay to pass a pointer to uninitialized memory as the memory is written to anyway.

However, ARG_PTR_TO_{LONG,INT} is a special case of ARG_PTR_TO_FIXED_SIZE_MEM just with additional alignment requirement. So it is better to just get rid of the ARG_PTR_TO_{LONG,INT} special cases altogether and reuse the fixed size memory types. For this, add MEM_ALIGNED to additionally ensure alignment given these helpers write directly into the args via = val. The .arg_size has been initialized reflecting the actual sizeof(*).

MEM_ALIGNED can only be used in combination with MEM_FIXED_SIZE annotated argument types, since in !MEM_FIXED_SIZE cases the verifier does not know the buffer size a priori and therefore cannot blindly write * = val.

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{
   affected: [],
   aliases: [
      "CVE-2024-49861",
   ],
   database_specific: {
      cwe_ids: [],
      github_reviewed: false,
      github_reviewed_at: null,
      nvd_published_at: "2024-10-21T13:15:06Z",
      severity: "HIGH",
   },
   details: "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix helper writes to read-only maps\n\nLonial found an issue that despite user- and BPF-side frozen BPF map\n(like in case of .rodata), it was still possible to write into it from\na BPF program side through specific helpers having ARG_PTR_TO_{LONG,INT}\nas arguments.\n\nIn check_func_arg() when the argument is as mentioned, the meta->raw_mode\nis never set. Later, check_helper_mem_access(), under the case of\nPTR_TO_MAP_VALUE as register base type, it assumes BPF_READ for the\nsubsequent call to check_map_access_type() and given the BPF map is\nread-only it succeeds.\n\nThe helpers really need to be annotated as ARG_PTR_TO_{LONG,INT} | MEM_UNINIT\nwhen results are written into them as opposed to read out of them. The\nlatter indicates that it's okay to pass a pointer to uninitialized memory\nas the memory is written to anyway.\n\nHowever, ARG_PTR_TO_{LONG,INT} is a special case of ARG_PTR_TO_FIXED_SIZE_MEM\njust with additional alignment requirement. So it is better to just get\nrid of the ARG_PTR_TO_{LONG,INT} special cases altogether and reuse the\nfixed size memory types. For this, add MEM_ALIGNED to additionally ensure\nalignment given these helpers write directly into the args via *<ptr> = val.\nThe .arg*_size has been initialized reflecting the actual sizeof(*<ptr>).\n\nMEM_ALIGNED can only be used in combination with MEM_FIXED_SIZE annotated\nargument types, since in !MEM_FIXED_SIZE cases the verifier does not know\nthe buffer size a priori and therefore cannot blindly write *<ptr> = val.",
   id: "GHSA-vf64-qg5h-qxhf",
   modified: "2024-12-14T21:31:32Z",
   published: "2024-10-21T15:32:27Z",
   references: [
      {
         type: "ADVISORY",
         url: "https://nvd.nist.gov/vuln/detail/CVE-2024-49861",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/1e75d25133158b525e0456876e9bcfd6b2993fd5",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/2ed98ee02d1e08afee88f54baec39ea78dc8a23c",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/32556ce93bc45c730829083cb60f95a2728ea48b",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/988e55abcf7fdb8fc9a76a7cf3f4e939a4d4fb3a",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/a2c8dc7e21803257e762b0bf067fd13e9c995da0",
      },
   ],
   schema_version: "1.4.0",
   severity: [
      {
         score: "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H",
         type: "CVSS_V3",
      },
   ],
}


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