linux-kernel - [PATCH 1/2] bpf: Allow bpf_user_ringbuf

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Date:   Wed, 12 Oct 2022 18:20:14 -0500
From:   David Vernet <void@...ifault.com>
To:     bpf@...r.kernel.org
Cc:     andrii@...nel.org, ast@...nel.org, martin.lau@...ux.dev,
        daniel@...earbox.net, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: [PATCH 1/2] bpf: Allow bpf_user_ringbuf_drain() callbacks to return 1

The bpf_user_ringbuf_drain() helper function allows a BPF program to
specify a callback that is invoked when draining entries from a
BPF_MAP_TYPE_USER_RINGBUF ring buffer map. The API is meant to allow the
callback to return 0 if it wants to continue draining samples, and 1 if
it's done draining. Unfortunately, bpf_user_ringbuf_drain() landed shortly
after commit 1bfe26fb0827 ("bpf: Add verifier support for custom
callback return range"), which changed the default behavior of callbacks
to only support returning 0.

This patch corrects that oversight by allowing bpf_user_ringbuf_drain()
callbacks to return 0 or 1. A follow-on patch will update the
user_ringbuf selftests to also return 1 from a bpf_user_ringbuf_drain()
callback to prevent this from regressing in the future.

Fixes: 205715673844 ("bpf: Add bpf_user_ringbuf_drain() helper")
Signed-off-by: David Vernet <void@...ifault.com>
---
 kernel/bpf/verifier.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6f6d2d511c06..9ab7188d8f68 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6946,6 +6946,7 @@ static int set_user_ringbuf_callback_state(struct bpf_verifier_env *env,
 	__mark_reg_not_init(env, &callee->regs[BPF_REG_5]);

 	callee->in_callback_fn = true;
+	callee->callback_ret_range = tnum_range(0, 1);
 	return 0;
 }

-- 
2.38.0