CVE-2022-48929 in Linux
Summary
by MITRE • 08/22/2024
In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix crash due to out of bounds access into reg2btf_ids.
When commit e6ac2450d6de ("bpf: Support bpf program calling kernel function") added kfunc support, it defined reg2btf_ids as a cheap way to translate the verifier reg type to the appropriate btf_vmlinux BTF ID, however commit c25b2ae13603 ("bpf: Replace PTR_TO_XXX_OR_NULL with PTR_TO_XXX | PTR_MAYBE_NULL") moved the __BPF_REG_TYPE_MAX from the last member of bpf_reg_type enum to after the base register types, and defined other variants using type flag composition. However, now, the direct usage of reg->type to index into reg2btf_ids may no longer fall into __BPF_REG_TYPE_MAX range, and hence lead to out of bounds access and kernel crash on dereference of bad pointer.
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Analysis
by VulDB Data Team • 11/26/2024
The vulnerability CVE-2022-48929 represents a critical out-of-bounds memory access issue within the Linux kernel's eBPF (extended Berkeley Packet Filter) subsystem that can lead to system crashes and potential privilege escalation. This flaw specifically affects the bpf program execution environment where kernel functions can be called from user-space programs through the bpf infrastructure. The vulnerability arises from a design inconsistency that occurred during kernel development when two separate commits modified the internal register type handling mechanism without proper synchronization of dependent data structures.
The technical root cause stems from the introduction of kfunc support in commit e6ac2450d6de which established the reg2btf_ids array as a mapping mechanism to translate verifier register types to appropriate BTF (BPF Type Format) IDs within the vmlinux BTF structure. However, subsequent commit c25b2ae13603 restructured the bpf_reg_type enum by moving __BPF_REG_TYPE_MAX to a different position and implementing type flag composition for variant register types. This change broke the direct indexing assumption that used reg->type as an array index into reg2btf_ids, since the register type values now exceed the original bounds defined by __BPF_REG_TYPE_MAX. The flaw manifests when bpf programs attempt to execute kernel function calls, causing the kernel to perform invalid memory accesses that result in immediate system crashes.
This vulnerability directly maps to CWE-129, which describes improper validation of array indices, and aligns with ATT&CK technique T1059.006 for execution through kernel modules or system calls. The operational impact extends beyond simple system instability as it affects the core security model of the Linux kernel's eBPF subsystem, which is used extensively for network filtering, system monitoring, and security enforcement. Attackers could potentially exploit this vulnerability to cause denial of service attacks or, in more sophisticated scenarios, achieve privilege escalation by carefully crafting malicious bpf programs that trigger the out-of-bounds access during kernel function calls.
The mitigation strategy requires immediate kernel updates that address the indexing logic in the bpf subsystem to ensure proper bounds checking before accessing the reg2btf_ids array. System administrators should prioritize patching affected kernel versions, particularly those running kernel versions between 5.15 and 5.19 where this vulnerability was introduced. Additionally, monitoring for suspicious bpf program execution patterns and implementing proper access controls for bpf program loading can help reduce the attack surface. The fix typically involves modifying the register type validation logic to properly account for the new enum structure while maintaining backward compatibility with existing bpf functionality. Organizations should also consider implementing runtime security controls that can detect and prevent malicious bpf program execution attempts that might trigger similar vulnerabilities in other kernel subsystems.