bpf: Fix mmap_lock deadlock on arena lock failure

Summary

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.

Timeline

1. Sep 17, 2026, 4:08 PM UTCCVE published
2. Oct 19, 2026, 9:01 AM UTCRecord last updated

Affected versions

• Linux Linux

  From b8467290edab4bafae352bf3f317055669a1a458 · fixed in af8087f16714f7620c4db3e732baaa1b2337948f; From b8467290edab4bafae352bf3f317055669a1a458 · fixed in 0b10b945479c954393d62ee3229d2f224a4ca91c

• Linux Linux

  7.0

• KernelLinux

  From 7.0.0 · fixed in 7.2.6

References 2