netdev - [PATCH bpf-next v6 3/8] bpf, iter: Fix the condition on p when calling stop.

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Date:   Mon,  1 Aug 2022 10:54:02 -0700
From:   Hao Luo <haoluo@...gle.com>
To:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        cgroups@...r.kernel.org, netdev@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        KP Singh <kpsingh@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Michal Koutny <mkoutny@...e.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        David Rientjes <rientjes@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        Hao Luo <haoluo@...gle.com>
Subject: [PATCH bpf-next v6 3/8] bpf, iter: Fix the condition on p when
 calling stop.

In bpf_seq_read, seq->op->next() could return an ERR and jump to
the label stop. However, the existing code in stop does not handle
the case when p (returned from next()) is an ERR. Adds the handling
of ERR of p by converting p into an error and jumping to done.

Because all the current implementations do not have a case that
returns ERR from next(), so this patch doesn't have behavior changes
right now.

Acked-by: Yonghong Song <yhs@...com>
Signed-off-by: Hao Luo <haoluo@...gle.com>
---
 kernel/bpf/bpf_iter.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 7e8fd49406f6..4688ba39ef25 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -198,6 +198,11 @@ static ssize_t bpf_seq_read(struct file *file, char __user *buf, size_t size,
 	}
 stop:
 	offs = seq->count;
+	if (IS_ERR(p)) {
+		seq->op->stop(seq, NULL);
+		err = PTR_ERR(p);
+		goto done;
+	}
 	/* bpf program called if !p */
 	seq->op->stop(seq, p);
 	if (!p) {
-- 
2.37.1.455.g008518b4e5-goog