On 9/20/23 11:07 AM, John Fastabend wrote:
pay much attention to their deletion. Compared with hash
maps, sockhash only provides spin_lock_bh protection.
This causes it to appear to have self-locking behavior
in the interrupt context, as CVE-2023-0160 points out.
CVE is a bit exagerrated in my opinion. I'm not sure why
anyone would delete an element from interrupt context. But,
OK if someone wrote such a thing we shouldn't lock up.
This should only happen in tracing program?
not sure if it will be too drastic to disallow tracing program to use
bpf_map_delete_elem during load time now.
A followup question, if sockmap can be accessed from tracing program, does it
need an in_nmi() check?
hash = sock_hash_bucket_hash(key, key_size);
bucket = sock_hash_select_bucket(htab, hash);
- spin_lock_bh(&bucket->lock);
+ spin_lock_irqsave(&bucket->lock, flags);
The hashtab code htab_lock_bucket also does a preempt_disable()
followed by raw_spin_lock_irqsave(). Do we need this as well
to handle the PREEMPT_CONFIG cases.
iirc, preempt_disable in htab is for the CONFIG_PREEMPT but it is for the
__this_cpu_inc_return to avoid unnecessary lock failure due to preemption, so
probably it is not needed here. The commit 2775da216287 ("bpf: Disable
preemption when increasing per-cpu map_locked")
If map_delete can be called from any tracing context, the raw_spin_lock_xxx
version is probably needed though. Otherwise, splat (e.g.
PROVE_RAW_LOCK_NESTING) could be triggered.
