bpf: Reject tail calls directly from callback frames
A tail call from a non-zero frame is modeled as a return from that frame.
The verifier makes R0 unknown and calls prepare_func_exit() for the taken
branch.
When the current frame is a synchronous callback, prepare_func_exit()
enforces the callback return-value contract and marks R0 precise. Since the
tail-call path synthesized R0 rather than deriving it from an instruction,
precision backtracking reaches the callback-calling instruction with R0
still requested and triggers the "callback unexpected regs" verifier bug.
A CAP_BPF task can therefore cause a WARN and an -EFAULT BPF_PROG_LOAD.
Tail calls reachable from callbacks are already rejected later by
check_max_stack_depth(). Reject a tail call made directly by a callback
before constructing the inconsistent return state, using the existing
diagnostic. Tail calls from ordinary subprograms keep their current
behavior.
Analysis
Analysis and contextual insights are available on OpenCVE Cloud.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
||||||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
No vendor fix or workaround currently provided.
Additional remediation guidance may be available on OpenCVE Cloud.
Tracking
Sign in to view the affected projects.
No advisories yet.
Fri, 25 Sep 2026 10:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: bpf: Reject tail calls directly from callback frames A tail call from a non-zero frame is modeled as a return from that frame. The verifier makes R0 unknown and calls prepare_func_exit() for the taken branch. When the current frame is a synchronous callback, prepare_func_exit() enforces the callback return-value contract and marks R0 precise. Since the tail-call path synthesized R0 rather than deriving it from an instruction, precision backtracking reaches the callback-calling instruction with R0 still requested and triggers the "callback unexpected regs" verifier bug. A CAP_BPF task can therefore cause a WARN and an -EFAULT BPF_PROG_LOAD. Tail calls reachable from callbacks are already rejected later by check_max_stack_depth(). Reject a tail call made directly by a callback before constructing the inconsistent return state, using the existing diagnostic. Tail calls from ordinary subprograms keep their current behavior. | |
| Title | bpf: Reject tail calls directly from callback frames | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-25T10:24:06.001Z
Reserved: 2026-09-25T10:19:56.073Z
Link: CVE-2026-98061
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-25T11:17:35.110
Modified: 2026-09-25T11:17:35.110
Link: CVE-2026-98061
Redhat
No data.
OpenCVE Enrichment
No data.
No weakness.