In the Linux kernel, the following vulnerability has been resolved: bpf, sockmap: Prevent lock inversion deadlock in map delete elem syzkaller started using corpuses where a BPF tracing program deletes elements from a sockmap/sockhash …

Overview

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

bpf, sockmap: Prevent lock inversion deadlock in map delete elem

syzkaller started using corpuses where a BPF tracing program deletes elements from a sockmap/sockhash map. Because BPF tracing programs can be invoked from any interrupt context, locks taken during a map_delete_elem operation must be hardirq-safe. Otherwise a deadlock due to lock inversion is possible, as reported by lockdep:

   CPU0                    CPU1
   ----                    ----

lock(&htab->buckets[i].lock); local_irq_disable(); lock(&host->lock); lock(&htab->buckets[i].lock); <Interrupt> lock(&host->lock);

Locks in sockmap are hardirq-unsafe by design. We expects elements to be deleted from sockmap/sockhash only in task (normal) context with interrupts enabled, or in softirq context.

Detect when map_delete_elem operation is invoked from a context which is not hardirq-unsafe, that is interrupts are disabled, and bail out with an error.

Note that map updates are not affected by this issue. BPF verifier does not allow updating sockmap/sockhash from a BPF tracing program today.

Affected

• linux_kernel >= 4.20, < 5.4.274
• linux_kernel >= 5.5, < 5.10.215
• linux_kernel >= 5.11, < 5.15.154
• linux_kernel >= 5.16, < 6.1.85
• linux_kernel >= 6.2, < 6.6.26
• linux_kernel >= 6.7, < 6.8.5
• linux_kernel = 6.9
• debian_linux = 10.0

Remediation

Upgrade past the affected range:

• linux_kernel 6.8.5