Withdrawn by the publisher.

In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix mmap_lock deadlock on arena lock failure

Reported by the Sashiko AI review.

arena_vm_fault() returns VM_FAULT_RETRY when it can't take arena->spinlock, but it never took mmap_lock. The fault path assumes a VM_FAULT_RETRY handler already dropped mmap_lock and re-takes it on the retry, so mmap_lock gets taken twice and can deadlock:

do_user_addr_fault() { fault = handle_mm_fault(...); // calls arena_vm_fault() if (fault & VM_FAULT_RETRY) goto retry; // re-locks mmap_lock mmap_read_unlock(mm); }

Return VM_FAULT_SIGBUS instead, for two reasons:

1. We could keep VM_FAULT_RETRY, but then we'd have to drop the fault lock first and cap the retry ourselves, the way __folio_lock_or_retry() does.

2. A failed raw_res_spin_lock_irqsave() already means a possible deadlock was detected, so retrying just hits the same lock again.

So returning VM_FAULT_RETRY here is overkill.

In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix mmap_lock deadlock on arena lock failure

Reported by the Sashiko AI review.

arena_vm_fault() returns VM_FAULT_RETRY when it can't take arena->spinlock, but it never took mmap_lock. The fault path assumes a VM_FAULT_RETRY handler already dropped mmap_lock and re-takes it on the retry, so mmap_lock gets taken twice and can deadlock:

do_user_addr_fault() { fault = handle_mm_fault(...); // calls arena_vm_fault() if (fault & VM_FAULT_RETRY) goto retry; // re-locks mmap_lock mmap_read_unlock(mm); }

Return VM_FAULT_SIGBUS instead, for two reasons:

1. We could keep VM_FAULT_RETRY, but then we'd have to drop the fault lock first and cap the retry ourselves, the way __folio_lock_or_retry() does.

2. A failed raw_res_spin_lock_irqsave() already means a possible deadlock was detected, so retrying just hits the same lock again.

So returning VM_FAULT_RETRY here is overkill.

kernel-devel-7.2.7-1.1 on GA media

Affected: Ubuntu:16.04:LTS: linux-hwe-edge, Ubuntu:18.04:LTS: linux-aws-5.0, Ubuntu:18.04:LTS: linux-aws-5.3, Ubuntu:18.04:LTS: linux-azure, Ubuntu:18.04:LTS: linux-azure-5.3, Ubuntu:18.04:LTS: linux-azure-edge, Ubuntu:18.04:LTS: linux-gcp, Ubuntu:18.04:LTS: linux-gcp-5.3, Ubuntu:18.04:LTS: linux-gke-4.15, Ubuntu:18.04:LTS: linux-gke-5.4 and 118 more

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix mmap_lock deadlock on arena lock failure Reported by the Sashiko AI review. arena_vm_fault() returns VM_FAULT_RETRY when it can't take arena->spinlock, but it never took mmap_lock. The fault path assumes a VM_FAULT_RETRY handler already dropped mmap_lock and re-takes it on the retry, so mmap_lock gets taken twice and can deadlock: do_user_addr_fault() { fault = handle_mm_fault(...); // calls arena_vm_fault() if (fault & VM_FAULT_RETRY) goto retry; // re-locks mmap_lock mmap_read_unlock(mm); } Return VM_FAULT_SIGBUS instead, for two reasons: 1. We could keep VM_FAULT_RETRY, but then we'd have to drop the fault lock first and cap the retry ourselves, the way __folio_lock_or_retry() does. 2. A failed raw_res_spin_lock_irqsave() already means a possible deadlock was detected, so retrying just hits the same lock again. So returning VM_FAULT_RETRY here is overkill.