CVE-2026-98644

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

bpf: Avoid soft lockup in __htab_map_lookup_and_delete_batch()

__htab_map_lookup_and_delete_batch() has no rescheduling point. The

batch count bounds how many entries are copied out, not how many

buckets are visited, so one BPF_MAP_LOOKUP_BATCH call can walk the

map end to end. The empty-bucket fast path is worse: it stays inside

a single rcu_read_lock() / bpf_disable_instrumentation() section for

any run of consecutive empty buckets.

That holds up on small maps, but it falls apart at scale. On a

144-CPU arm64 host running a CONFIG_PREEMPT_NONE kernel, periodic

BPF_MAP_LOOKUP_BATCH calls against an LRU hash map with 16,777,216

buckets held a CPU inside the batch op for 77+ seconds and triggered

the soft lockup watchdog.

Commit 75134f16e7dd ("bpf: Add schedule points in batch ops") fixed this

same problem in the generic batch ops, but not in this htab-native path,

which every htab-based hash map variant uses for its lookup[_and_delete]

batch ops.

Complete that fix here. Leave the critical section after 64 consecutive

empty buckets, call cond_resched_tasks_rcu_qs(), and resume at the saved

bucket cursor. No locks are held at that point, and resuming from the

cursor is already the function's behavior for non-empty buckets. Add the

same call to the per-bucket loop after copy_to_user(), where every lock

has been dropped. cond_resched_rcu() is not enough here: sleeping with

bpf_prog_active elevated makes tracing programs on that CPU silently

skip their invocations.

Plain cond_resched() is not enough either. It is a no-op under PREEMPT

and PREEMPT_LAZY, the only models arm64 and x86 have offered since

commit 7dadeaa6e851 ("sched: Further restrict the preemption modes").

It is also never a Tasks RCU quiescent state, in any model: the

reschedule counts as a preemption. The walking task stays a holdout and

stalls every synchronize_rcu_tasks() caller, ftrace and BPF trampoline

teardown included, until the syscall returns [1].

cond_resched_tasks_rcu_qs() is the usual tool for that [2]. It reports

the quiescent state at each yield and still reschedules as

cond_resched() does on PREEMPT_NONE and PREEMPT_VOLUNTARY kernels.