GHSA-WQ8M-PJJR-X46W
Vulnerability from github – Published: 2026-09-25 12:31 – Updated: 2026-09-25 12:31In the Linux kernel, the following vulnerability has been resolved:
bpf: Reject legacy packet loads from callbacks
check_ld_abs() models a failed BPF_LD_ABS or BPF_LD_IND in a subprogram as an implicit return with R0 set to zero. It calls prepare_func_exit() to explore this synthesized path.
When the load is reached directly from a synchronous callback, prepare_func_exit() enforces the callback return contract and marks R0 precise. R0 is not derived from a real instruction on this path, so precision backtracking reaches the callback call with R0 still requested and triggers the "callback unexpected regs" verifier bug. A privileged program loader can therefore cause a verifier warning and an -EFAULT BPF_PROG_LOAD.
These legacy packet-load instructions are deprecated. Reject them from callbacks rather than complicating their implicit-return model. Check all active frames before constructing the implicit return so nested static subprograms cannot hide the callback context.
Global functions are verified independently with a fresh frame zero, so an active-frame check cannot identify a global function called from a callback. Also check the complete subprogram call graph during stack-depth validation and reject a function containing a legacy load when any caller is a callback. This covers global and static descendants without making has_ld_abs transitive, preserving its per-function BTF return-type check. Ordinary uses outside callbacks remain supported.
{
"affected": [],
"aliases": [
"CVE-2026-98044"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-25T11:17:33Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject legacy packet loads from callbacks\n\ncheck_ld_abs() models a failed BPF_LD_ABS or BPF_LD_IND in a\nsubprogram as an implicit return with R0 set to zero. It calls\nprepare_func_exit() to explore this synthesized path.\n\nWhen the load is reached directly from a synchronous callback,\nprepare_func_exit() enforces the callback return contract and marks R0\nprecise. R0 is not derived from a real instruction on this path, so\nprecision backtracking reaches the callback call with R0 still requested\nand triggers the \"callback unexpected regs\" verifier bug. A privileged\nprogram loader can therefore cause a verifier warning and an -EFAULT\nBPF_PROG_LOAD.\n\nThese legacy packet-load instructions are deprecated. Reject them from\ncallbacks rather than complicating their implicit-return model. Check all\nactive frames before constructing the implicit return so nested static\nsubprograms cannot hide the callback context.\n\nGlobal functions are verified independently with a fresh frame zero, so\nan active-frame check cannot identify a global function called from a\ncallback. Also check the complete subprogram call graph during stack-depth\nvalidation and reject a function containing a legacy load when any caller\nis a callback. This covers global and static descendants without making\nhas_ld_abs transitive, preserving its per-function BTF return-type check.\nOrdinary uses outside callbacks remain supported.",
"id": "GHSA-wq8m-pjjr-x46w",
"modified": "2026-09-25T12:31:34Z",
"published": "2026-09-25T12:31:34Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98044"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3484a99303912db62428494a9061212049027e57"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/bc489c0c9b8c86bd7fac42cfd1bb152f042fca56"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e7d28823c662128caae63f14e16bd394916c139b"
}
],
"schema_version": "1.4.0",
"severity": []
}
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