ghsa-27cc-fvv7-2rh9
Vulnerability from github
In the Linux kernel, the following vulnerability has been resolved:
bpf: put bpf_link's program when link is safe to be deallocated
In general, BPF link's underlying BPF program should be considered to be reachable through attach hook -> link -> prog chain, and, pessimistically, we have to assume that as long as link's memory is not safe to free, attach hook's code might hold a pointer to BPF program and use it.
As such, it's not (generally) correct to put link's program early before waiting for RCU GPs to go through. More eager bpf_prog_put() that we currently do is mostly correct due to BPF program's release code doing similar RCU GP waiting, but as will be shown in the following patches, BPF program can be non-sleepable (and, thus, reliant on only "classic" RCU GP), while BPF link's attach hook can have sleepable semantics and needs to be protected by RCU Tasks Trace, and for such cases BPF link has to go through RCU Tasks Trace + "classic" RCU GPs before being deallocated. And so, if we put BPF program early, we might free BPF program before we free BPF link, leading to use-after-free situation.
So, this patch defers bpf_prog_put() until we are ready to perform bpf_link's deallocation. At worst, this delays BPF program freeing by one extra RCU GP, but that seems completely acceptable. Alternatively, we'd need more elaborate ways to determine BPF hook, BPF link, and BPF program lifetimes, and how they relate to each other, which seems like an unnecessary complication.
Note, for most BPF links we still will perform eager bpf_prog_put() and link dealloc, so for those BPF links there are no observable changes whatsoever. Only BPF links that use deferred dealloc might notice slightly delayed freeing of BPF programs.
Also, to reduce code and logic duplication, extract program put + link dealloc logic into bpf_link_dealloc() helper.
{
"affected": [],
"aliases": [
"CVE-2024-56786"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-01-08T18:15:19Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: put bpf_link\u0027s program when link is safe to be deallocated\n\nIn general, BPF link\u0027s underlying BPF program should be considered to be\nreachable through attach hook -\u003e link -\u003e prog chain, and, pessimistically,\nwe have to assume that as long as link\u0027s memory is not safe to free,\nattach hook\u0027s code might hold a pointer to BPF program and use it.\n\nAs such, it\u0027s not (generally) correct to put link\u0027s program early before\nwaiting for RCU GPs to go through. More eager bpf_prog_put() that we\ncurrently do is mostly correct due to BPF program\u0027s release code doing\nsimilar RCU GP waiting, but as will be shown in the following patches,\nBPF program can be non-sleepable (and, thus, reliant on only \"classic\"\nRCU GP), while BPF link\u0027s attach hook can have sleepable semantics and\nneeds to be protected by RCU Tasks Trace, and for such cases BPF link\nhas to go through RCU Tasks Trace + \"classic\" RCU GPs before being\ndeallocated. And so, if we put BPF program early, we might free BPF\nprogram before we free BPF link, leading to use-after-free situation.\n\nSo, this patch defers bpf_prog_put() until we are ready to perform\nbpf_link\u0027s deallocation. At worst, this delays BPF program freeing by\none extra RCU GP, but that seems completely acceptable. Alternatively,\nwe\u0027d need more elaborate ways to determine BPF hook, BPF link, and BPF\nprogram lifetimes, and how they relate to each other, which seems like\nan unnecessary complication.\n\nNote, for most BPF links we still will perform eager bpf_prog_put() and\nlink dealloc, so for those BPF links there are no observable changes\nwhatsoever. Only BPF links that use deferred dealloc might notice\nslightly delayed freeing of BPF programs.\n\nAlso, to reduce code and logic duplication, extract program put + link\ndealloc logic into bpf_link_dealloc() helper.",
"id": "GHSA-27cc-fvv7-2rh9",
"modified": "2025-01-10T21:31:27Z",
"published": "2025-01-08T18:30:49Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-56786"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2fcb921c2799c49ac5e365cf4110f94a64ae4885"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5fe23c57abadfd46a7a66e81f3536e4757252a0b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f44ec8733a8469143fde1984b5e6931b2e2f6f3f"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.