CVE-2024-35895

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.