GHSA-V7FM-VJVQ-9FG6
Vulnerability from github – Published: 2024-06-19 15:30 – Updated: 2024-10-31 15:30In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix kernel address leakage in atomic fetch
The change in commit 37086bfdc737 ("bpf: Propagate stack bounds to registers in atomics w/ BPF_FETCH") around check_mem_access() handling is buggy since this would allow for unprivileged users to leak kernel pointers. For example, an atomic fetch/and with -1 on a stack destination which holds a spilled pointer will migrate the spilled register type into a scalar, which can then be exported out of the program (since scalar != pointer) by dumping it into a map value.
The original implementation of XADD was preventing this situation by using a double call to check_mem_access() one with BPF_READ and a subsequent one with BPF_WRITE, in both cases passing -1 as a placeholder value instead of register as per XADD semantics since it didn't contain a value fetch. The BPF_READ also included a check in check_stack_read_fixed_off() which rejects the program if the stack slot is of __is_pointer_value() if dst_regno < 0. The latter is to distinguish whether we're dealing with a regular stack spill/ fill or some arithmetical operation which is disallowed on non-scalars, see also 6e7e63cbb023 ("bpf: Forbid XADD on spilled pointers for unprivileged users") for more context on check_mem_access() and its handling of placeholder value -1.
One minimally intrusive option to fix the leak is for the BPF_FETCH case to initially check the BPF_READ case via check_mem_access() with -1 as register, followed by the actual load case with non-negative load_reg to propagate stack bounds to registers.
{
"affected": [],
"aliases": [
"CVE-2021-47608"
],
"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 fetch\n\nThe change in commit 37086bfdc737 (\"bpf: Propagate stack bounds to registers\nin atomics w/ BPF_FETCH\") around check_mem_access() handling is buggy since\nthis would allow for unprivileged users to leak kernel pointers. For example,\nan atomic fetch/and with -1 on a stack destination which holds a spilled\npointer will migrate the spilled register type into a scalar, which can then\nbe exported out of the program (since scalar != pointer) by dumping it into\na map value.\n\nThe original implementation of XADD was preventing this situation by using\na double call to check_mem_access() one with BPF_READ and a subsequent one\nwith BPF_WRITE, in both cases passing -1 as a placeholder value instead of\nregister as per XADD semantics since it didn\u0027t contain a value fetch. The\nBPF_READ also included a check in check_stack_read_fixed_off() which rejects\nthe program if the stack slot is of __is_pointer_value() if dst_regno \u003c 0.\nThe latter is to distinguish whether we\u0027re dealing with a regular stack spill/\nfill or some arithmetical operation which is disallowed on non-scalars, see\nalso 6e7e63cbb023 (\"bpf: Forbid XADD on spilled pointers for unprivileged\nusers\") for more context on check_mem_access() and its handling of placeholder\nvalue -1.\n\nOne minimally intrusive option to fix the leak is for the BPF_FETCH case to\ninitially check the BPF_READ case via check_mem_access() with -1 as register,\nfollowed by the actual load case with non-negative load_reg to propagate\nstack bounds to registers.",
"id": "GHSA-v7fm-vjvq-9fg6",
"modified": "2024-10-31T15:30:58Z",
"published": "2024-06-19T15:30:55Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-47608"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/423628125a484538111c2c6d9bb1588eb086053b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7d3baf0afa3aa9102d6a521a8e4c41888bb79882"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N",
"type": "CVSS_V3"
}
]
}
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