[PATCH bpf-next] bpf: check signal validity in nmi for bpf_send_signal() helper

[PATCH bpf-next] bpf: check signal validity in nmi for bpf_send_signal() helper

[Yonghong Song]

Commit 8b401f9ed244 ("bpf: implement bpf_send_signal() helper")
introduced bpf_send_signal() helper. If the context is nmi,
the sending signal work needs to be deferred to irq_work.
If the signal is invalid, the error will appear in irq_work
and it won't be propagated to user.

This patch did an early check in the helper itself to
notify user invalid signal, as suggested by Daniel.

Signed-off-by: Yonghong Song <yhs@fb.com>
---
 kernel/trace/bpf_trace.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 70029eafc71f..fe73926a07cd 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -600,6 +600,12 @@ BPF_CALL_1(bpf_send_signal, u32, sig)
 		return -EPERM;
 
 	if (in_nmi()) {
+		/* Do an early check on signal validity. Otherwise,
+		 * the error is lost in deferred irq_work.
+		 */
+		if (unlikely(!valid_signal(sig)))
+			return -EINVAL;
+
 		work = this_cpu_ptr(&send_signal_work);
 		if (work->irq_work.flags & IRQ_WORK_BUSY)
 			return -EBUSY;
-- 
2.17.1

Re: [PATCH bpf-next] bpf: check signal validity in nmi for bpf_send_signal() helper

[Daniel Borkmann]

On 05/25/2019 08:57 PM, Yonghong Song wrote:
> Commit 8b401f9ed244 ("bpf: implement bpf_send_signal() helper")
> introduced bpf_send_signal() helper. If the context is nmi,
> the sending signal work needs to be deferred to irq_work.
> If the signal is invalid, the error will appear in irq_work
> and it won't be propagated to user.
> 
> This patch did an early check in the helper itself to
> notify user invalid signal, as suggested by Daniel.
> 
> Signed-off-by: Yonghong Song <yhs@fb.com>

Applied, thanks!