CVE-2026-31592 in Linux
Resumen
por VulDB • 2026-05-17
Based on the provided crash dump and syzlang reproducer, the issue appears to be a kernel panic or oops occurring during KVM operations, specifically involving `KVM_SET_GUEST_DEBUG` and `KVM_RUN` on a vCPU. The register state shows a crash in a context that likely involves memory management or KVM internal structures.
The request is to refactor the code (presumably the kernel fix or the test harness logic, but given the context of "syzlang reproducer" and "guard()", this is likely a request to improve the **kernel source code** handling this bug, or potentially the **syzkaller test generation logic** if it were a user-space tool. However, "Opportunistically use guard()..." is a common pattern in **Linux kernel C code** to simplify error handling paths.
Since I am an AI assistant and the user provided a crash log and a reproducer, but **did not provide the actual kernel source code** that needs to be fixed, I cannot directly modify the kernel source.
However, I can provide a **hypothetical example** of how one might use `guard()` in a kernel function that handles `KVM_SET_GUEST_DEBUG` or similar ioctls to simplify error handling, assuming a typical pattern where resources are allocated and need cleanup on error.
### Hypothetical Kernel Code Refactoring Example
Let's assume there is a function `kvm_vm_ioctl_set_guest_debug` in `arch/x86/kvm/x86.c` (or similar) that currently looks like this (simplified):
```c // BEFORE: Traditional error handling with goto static int kvm_vm_ioctl_set_guest_debug(struct kvm *kvm, struct kvm_guest_debug *dbg) {
int r; struct kvm_vcpu *vcpu;
r = kvm_vcpu_try_get(kvm, dbg->vcpu_id, &vcpu); if (r) return r;
// Some complex setup that might fail r = kvm_arch_vcpu_setup_debug(vcpu, dbg); if (r) goto out_put_vcpu;
// More setup... r = kvm_arch_vcpu_apply_debug(vcpu, dbg); if (r) goto out_put_vcpu;
// Success return 0;
out_put_vcpu: kvm_vcpu_put(vcpu); return r; } ```
Using `guard()` (introduced in recent kernels to simplify cleanup), we can rewrite it as:
```c // AFTER: Using guard() for automatic cleanup static int kvm_vm_ioctl_set_guest_debug(struct kvm *kvm, struct kvm_guest_debug *dbg) {
int r; struct kvm_vcpu *vcpu;
r = kvm_vcpu_try_get(kvm, dbg->vcpu_id, &vcpu); if (r) return r;
// Use guard() to automatically call kvm_vcpu_put(vcpu) when leaving the scope guard(kvm_vcpu_put)(vcpu);
// Some complex setup that might fail r = kvm_arch_vcpu_setup_debug(vcpu, dbg); if (r) return r;
// More setup... r = kvm_arch_vcpu_apply_debug(vcpu, dbg); if (r) return r;
// Success return 0; } ```
### Explanation
1. **`guard(kvm_vcpu_put)(vcpu);`**: This macro creates a cleanup action that will be executed when the variable `vcpu` goes out of scope (i.e., when the function returns, whether normally or via an early `return`). 2. **Simplified Error Paths**: Instead of jumping to a `goto` label (`out_put_vcpu`), we can simply `return r` on error. The `guard()` ensures that `kvm_vcpu_put(vcpu)` is called before the return. 3. **Opportunistic Use**: The term "opportunistic" suggests that if the code structure allows it (i.e., the resource to be cleaned up is known and the cleanup function is simple), using `guard()` is preferred over adding new error labels and `goto` statements.
### Note on the Crash
The crash dump provided (`RBP: 00007f34ea000d69`, etc.) and the syzlang reproducer suggest a bug in the KVM subsystem, possibly related to: - Invalid memory access in `KVM_SET_GUEST_DEBUG`. - Race conditions with vCPU creation/destruction. - Issues with `KVM_RUN` after debug setup.
To fix the actual bug, one would need to: 1. Analyze the crash address and register state. 2. Identify the exact line of code causing the oops. 3. Determine if it's a null pointer dereference, use-after-free, or bounds check issue. 4. Apply
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