diff options
| author | Yuan Chen <chenyuan@kylinos.cn> | 2026-10-09 10:24:27 +0800 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2026-10-16 18:41:07 +0000 |
| commit | 2d1f101ee619435873ed8a23fcb3bd09204a5024 (patch) | |
| tree | 329b092c173242ffbadcc1687d2f997010c1e8d8 /kernel/trace | |
| parent | d2141481a764efdfaac70965ea28e8925f6a6b80 (diff) | |
bpf: Claim the per-CPU send_signal irq_work before filling it
irq_work_is_busy() cannot see the per-CPU send_signal_work while
it is being filled: the check only matches after irq_work_queue()
has claimed the work. A concurrent caller therefore passes it, both
callers race for the same irq_work, and the loser's signal is
silently lost along with its task reference while the queued work
runs with a mix of both callers' fields.
kprobe, tracepoint and perf_event programs exclude each other on
the same CPU through bpf_prog_active, so for two callers to meet,
one of the programs has to be a raw tracepoint or an fentry one.
And since commit 87c544108b61 ("bpf: Send signals asynchronously
if !preemptible") this path runs with IRQs enabled too, so a hard
IRQ can interrupt the fill as well, not only an NMI. Found by code
inspection and reproduced with a perf_event NMI program racing an
fentry one.
Claim the work through work->task itself: cmpxchg() it from NULL
to the target task before touching the other fields, and set it
back to NULL once the callback has consumed them. A context
finding the work claimed returns the documented -EBUSY.
Fixes: 1bc7896e9ef4 ("bpf: Fix deadlock with rq_lock in bpf_send_signal()")
Signed-off-by: Yuan Chen <chenyuan@kylinos.cn>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20261009022427.968304-1-chenyuan@kylinos.cn
Diffstat (limited to 'kernel/trace')
| -rw-r--r-- | kernel/trace/bpf_trace.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 195f78db9bda..5465e7eba238 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -823,6 +823,7 @@ const struct bpf_func_proto bpf_task_pt_regs_proto = { struct send_signal_irq_work { struct irq_work irq_work; + /* The claim: NULL marks the slot free for the next caller. */ struct task_struct *task; u32 sig; enum pid_type type; @@ -842,6 +843,8 @@ static void do_bpf_send_signal(struct irq_work *entry) group_send_sig_info(work->sig, siginfo, work->task, work->type); put_task_struct(work->task); + /* Release once the fields are consumed. */ + smp_store_release(&work->task, NULL); } static int bpf_send_signal_common(u32 sig, enum pid_type type, struct task_struct *task, u64 value) @@ -885,14 +888,14 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type, struct task_struc return -EINVAL; work = this_cpu_ptr(&send_signal_work); - if (irq_work_is_busy(&work->irq_work)) + if (cmpxchg(&work->task, NULL, task)) return -EBUSY; /* Add the current task, which is the target of sending signal, * to the irq_work. The current task may change when queued * irq works get executed. */ - work->task = get_task_struct(task); + get_task_struct(task); work->has_siginfo = siginfo == &info; if (work->has_siginfo) copy_siginfo(&work->info, &info); |