CVE-2026-90312 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Check load-acquire src ptr type before the load
check_atomic_load() calls check_load_mem() before atomic_ptr_type_ok(). For a load-acquire that fetches into its own source register (dst_reg == src_reg), check_load_mem() overwrites src_reg's type with the type of the loaded value, so the subsequent atomic_ptr_type_ok() no longer sees the source pointer and fails to reject the disallowed types (ctx, pkt, flow_keys, sock).
Since bpf_convert_ctx_accesses() does not rewrite atomic loads, the raw access to the underlying kernel object is left in place. The destination type is taken from the ctx access itself, so a load-acquire of the sk field of struct __sk_buff for example leaves the register typed as PTR_TO_SOCK_COMMON_OR_NULL, which type_is_sk_pointer() does not match either, while it actually holds unconverted struct sk_buff bytes. Once the NULL check has passed this is a type confusion, not just a leak of kernel data.
Validate src_reg with check_reg_arg() and check the source pointer type with atomic_ptr_type_ok() before the load again, mirroring check_atomic_rmw(). Out-of-range register numbers are already rejected earlier by check_and_resolve_insns() (commit 503d21ef8eac ("bpf: Do register range validation early")), and the only exemption there, is_stack_arg_ldx(), requires BPF_LDX | BPF_MEM | BPF_DW and thus never matches a BPF_ATOMIC insn. atomic_ptr_type_ok() can therefore not dereference register state out of bounds, that is, the out-of-bounds read addressed by the Fixes commit below does not reappear (as proven also via selftest).
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel's Berkeley Packet Filter subsystem contains a critical logic flaw within its verifier component related to atomic load operations. Specifically, the function check_atomic_load() invokes check_load_mem() prior to validating whether the source pointer type is permissible for atomic access using atomic_ptr_type_ok(). This ordering creates a race condition in state validation where a BPF program performing a load-acquire operation that writes into its own source register triggers an unintended side effect. During this process, check_load_mem() overwrites the type information of the source register with the type corresponding to the value being loaded from memory rather than preserving the original pointer type. Consequently, when atomic_ptr_type_ok subsequently executes, it evaluates the modified register state instead of the actual source pointer, causing it to fail in rejecting disallowed types such as context pointers, packet data references, flow keys, or socket structures that are not permitted for atomic operations.
This vulnerability results in a severe type confusion issue within kernel memory management. Because the BPF verifier fails to correctly identify and reject invalid atomic loads on restricted pointer types, raw accesses to underlying kernel objects remain unconverted and unchecked. For instance, when an attacker crafts a load-acquire instruction targeting fields like sk within struct __sk_buff, the destination register is typed as PTR_TO_SOCK_COMMON_OR_NULL based on the context access itself rather than reflecting the actual memory content. While type_is_sk_pointer may not match this incorrect typing, the register actually holds unconverted bytes from the kernel structure. Once a subsequent NULL check passes due to the misleading type information, the verifier allows execution of code that interprets raw kernel data as a specific object type, leading to potential exploitation scenarios beyond simple information leaks.
The operational impact of this flaw extends significantly beyond data exfiltration. By allowing unconverted access to sensitive kernel structures through atomic load instructions, an attacker can potentially achieve arbitrary read or write primitives depending on how the confused types are utilized in subsequent BPF program logic. This undermines the fundamental security guarantees provided by the eBPF sandboxing mechanism, which relies heavily on strict type checking and memory safety validations during JIT compilation preparation. The flaw effectively bypasses restrictions designed to prevent user-space programs from interacting with kernel internals via atomic operations, thereby exposing critical subsystems like networking stack components to potential compromise.
To mitigate this vulnerability, developers have implemented a fix that reorders the validation steps within check_atomic_load(). The source register is now validated using check_reg_arg() and its pointer type is verified against allowed types for atomic access via atomic_ptr_type_ok before any memory load operation occurs. This approach mirrors the logic used in check_atomic_rmw(), ensuring consistent security checks across different atomic instruction types. Additionally, out-of-range register numbers are already rejected earlier by check_and_resolve_insns, which prevents dereferencing errors during this validation phase. The exemption for stack argument loads does not apply to BPF_ATOMIC instructions due to specific opcode constraints, thereby eliminating the risk of out-of-bounds reads associated with previous fixes.
From a classification perspective, this vulnerability aligns with CWE-841 Improper Enforcement of Behavioral Workflow and CWE-20 Incorrect Processing Logic within the context of input validation for security-critical systems. It also relates to CWE-697 Incorrect Comparison during Integrity Checks due to the failure in verifying pointer types before memory access. In terms of adversarial tactics, this flaw could be leveraged by attackers aiming to escalate privileges or bypass sandbox restrictions as described under MITRE ATT&CK technique T1055 Process Injection if combined with other exploitation primitives, though primarily it represents a violation of intended execution flow and type safety mechanisms inherent in the kernel's BPF implementation.