CVE-2026-90299 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix sleepable check for tracing/lsm prog
When CONFIG_FUNCTION_ERROR_INJECTION is disabled, a sleepable tracing prog is allowed to attach to '__x64_'-alike prefix symbols.
It is because the verifier does not verify whether the symbol is a kernel function or a bpf prog. That said, a sleepable tracing prog is allowed to attach to a bpf prog target whose name has '__x64_'-alike prefix.
For example, a sleepable fentry prog attaches to a '__x64_sys_nop' XDP prog, and copies buffer from a user pointer with bpf_copy_from_user() helper. After attaching the XDP prog to lo interface, the kernel BUG could be triggered by 'ping -c 1 -W 1 127.0.0.1':
[ 3.460756] BUG: sleeping function called from invalid context at kernel/bpf/trampoline.c:1324
Fix it by disallowing sleepable prog always when its target btf is not a kernel's btf.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel contains a critical vulnerability within the BPF verifier subsystem related to the attachment of sleepable tracing programs, specifically affecting scenarios where function error injection configuration is disabled. This flaw arises from an insufficient validation mechanism that fails to distinguish between kernel functions and other BPF program targets when determining whether a sleeping context is permissible. The core issue lies in the logic used to identify valid attachment points for sleepable fentry or tracepoint programs. Historically, the verifier relied on symbol naming conventions, specifically checking if the target symbol name contained prefixes such as '_x64', which are typically associated with kernel functions that might be safe for certain types of tracing operations under specific conditions. However, this heuristic is flawed because it does not verify whether the underlying BTF (BPF Type Format) metadata actually corresponds to a kernel module or binary versus another user-space loaded BPF program. Consequently, if a symbol name mimics the expected pattern but belongs to a different domain, such as an XDP program, the verifier incorrectly permits the attachment of a sleepable tracing program.
This technical oversight leads to severe operational instability and potential denial-of-service conditions within the kernel environment. When a sleepable BPF program is attached to an incompatible target like an XDP program, it violates fundamental kernel constraints regarding execution context. Specifically, certain helpers invoked by these programs, such as bpf_copy_from_user(), are designed to potentially sleep while waiting for data or resources. In standard kernel functions, this might be handled appropriately depending on the scheduling context, but when executed within the rigid and non-sleepable contexts often associated with network processing paths like XDP, invoking a sleeping function triggers an immediate kernel panic. The system responds with a BUG message indicating that a sleeping function was called from an invalid context, effectively crashing the host machine or disrupting critical network services running on loopback interfaces as demonstrated by simple ping commands triggering the fault path through the trampoline code in kernel/bpf/trampoline.c.
From a security and standards perspective, this vulnerability aligns with CWE-20 Improper Input Validation, where the system fails to adequately validate the nature of the target object before allowing an operation that assumes specific execution properties. It also relates to CWE-697 Incorrect Comparison, as the verifier relies on string prefix matching rather than robust type and context verification via BTF metadata. In terms of MITRE ATT&CK for Enterprise or ICS, this could be categorized under T1498 Network Denial of Service if exploited by a malicious actor with access to load eBPF programs, allowing them to crash the system simply by crafting a program that attaches incorrectly due to name collision or confusion. The lack of strict context validation allows an unprivileged user who can load BPF programs to destabilize the entire kernel, violating the principle of least privilege and isolation between different subsystems within the Linux kernel architecture.
To mitigate this vulnerability, it is essential to enforce stricter verification rules that decouple attachment permissions from superficial symbol naming conventions. The primary fix involves modifying the verifier logic to always disallow sleepable programs when their target BTF does not originate from the main kernel's BTF database. This ensures that only actual kernel functions, which have been audited and deemed safe for such operations under specific configurations, can be targets for sleepable tracing probes. By checking the origin of the BTF data rather than just the symbol name string, the system prevents the attachment to user-space loaded programs like XDP or other eBPF binaries that do not support sleeping contexts. This change restores the integrity of execution context boundaries and prevents the triggering of kernel bugs through invalid helper calls in inappropriate scheduling environments. System administrators should ensure their kernels are updated with patches addressing this specific verifier logic, and developers writing BPF applications must adhere to strict guidelines regarding which targets can accept sleepable probes, relying on explicit type checks rather than heuristic name matching.