CVE-2026-98062
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Mark signal tracepoint siginfo arguments as scalar
The signal_generate and signal_deliver tracepoints declare their info argument as a struct kernel_siginfo pointer. btf_ctx_access() therefore treats it as a trusted pointer for tp_btf programs.
Signal delivery also uses SEND_SIG_NOINFO and SEND_SIG_PRIV as special values for this argument. Those values are zero and one respectively, and are not pointers. A tp_btf program can currently dereference either value and fault the kernel. In particular, signal_generate can run from timer interrupt context, turning the fault into a kernel panic.
Record both tracepoints in raw_tp_null_args[] and mark argument one as
a non-pointer. This preserves scalar access to the cookie while rejecting direct and helper-mediated pointer use. Merely marking it nullable would not suffice because SEND_SIG_PRIV is nonzero.
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Analysis
by VulDB Data Team • 09/25/2026
The Linux kernel contains a vulnerability within its Berkeley Packet Filter subsystem related to the handling of signal tracepoint arguments, specifically involving the signal_generate and signal_deliver functions. These tracepoints declare their info argument as a pointer to struct kernel_siginfo, which leads the BTF context access mechanism to treat this parameter as a trusted pointer for tp_btf programs. This assumption creates a critical mismatch because signal delivery mechanisms utilize SEND_SIG_NOINFO and SEND_SIG_PRIV as special sentinel values rather than actual memory addresses. These specific constants are represented by zero and one respectively, meaning they do not correspond to valid kernel memory locations that can be safely dereferenced.
When a tp_btf program attempts to access the first argument of these tracepoints under the current implementation, it interprets the scalar values zero or one as pointers. Attempting to dereference either value results in an invalid memory access fault within the kernel space. The severity of this issue is significantly amplified by the execution context in which signal_generate operates. Because this function can be invoked from timer interrupt context, a resulting page fault cannot be handled gracefully through standard exception handling mechanisms that might allow for process termination or error recovery. Instead, such an invalid memory access triggers an immediate kernel panic, leading to a complete system crash and denial of service condition without requiring any external interaction beyond the triggering of specific signal-related events.
The root cause of this vulnerability lies in the incorrect classification of tracepoint arguments by the BTF context access logic. By treating scalar sentinel values as trusted pointers, the kernel fails to enforce appropriate boundary checks on data types passed through these interfaces. This flaw allows user-space programs with eBPF capabilities to induce instability simply by interacting with signal delivery paths that utilize non-pointer argument representations. The vulnerability highlights a gap in how special constant arguments are validated against their declared structural types within the tracing infrastructure, allowing for type confusion between scalar integers and pointer references.
To mitigate this risk, the kernel developers have implemented a fix that explicitly marks the first argument of both signal_generate and signal_deliver tracepoints as non-pointer data using raw_tp_null_args registration. This change ensures that while programs can still access the cookie value associated with these events, any attempt to perform direct or helper-mediated pointer dereferences on this specific argument is rejected by the verifier. Merely marking the argument as nullable would have been insufficient because SEND_SIG_PRIV has a nonzero value of one, which could potentially be mistaken for a valid low-memory address if not explicitly constrained against pointer operations. This correction preserves necessary scalar access while strictly preventing invalid memory accesses that lead to kernel panics.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer, as it involves treating non-pointer data as pointers leading out-of-bounds access. In terms of adversarial tactics, this could be leveraged in an ATT&CK context under T1499 Endpoint Denial of Service or potentially T1053 Scheduled Task/Job if used to crash systems via scheduled signal events. The fix demonstrates the importance of rigorous type checking for tracepoint arguments that may contain sentinel values rather than actual memory references, ensuring that eBPF programs cannot exploit ambiguous argument types to destabilize kernel integrity.