linux-kernel - [PATCH AUTOSEL 4.18 07/92] bpf: fix rcu annotations in compute_effective

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Message-ID: <20180915012944.179481-7-alexander.levin@microsoft.com>
Date:   Sat, 15 Sep 2018 01:29:53 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Roman Gushchin <guro@...com>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.18 07/92] bpf: fix rcu annotations in
 compute_effective_progs()

From: Roman Gushchin <guro@...com>

[ Upstream commit 3960f4fd6585608e8cc285d9665821985494e147 ]

The progs local variable in compute_effective_progs() is marked
as __rcu, which is not correct. This is a local pointer, which
is initialized by bpf_prog_array_alloc(), which also now
returns a generic non-rcu pointer.

The real rcu-protected pointer is *array (array is a pointer
to an RCU-protected pointer), so the assignment should be performed
using rcu_assign_pointer().

Fixes: 324bda9e6c5a ("bpf: multi program support for cgroup+bpf")
Signed-off-by: Roman Gushchin <guro@...com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 kernel/bpf/cgroup.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 3d83ee7df381..badabb0b435c 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -95,7 +95,7 @@ static int compute_effective_progs(struct cgroup *cgrp,
 				   enum bpf_attach_type type,
 				   struct bpf_prog_array __rcu **array)
 {
-	struct bpf_prog_array __rcu *progs;
+	struct bpf_prog_array *progs;
 	struct bpf_prog_list *pl;
 	struct cgroup *p = cgrp;
 	int cnt = 0;
@@ -120,13 +120,12 @@ static int compute_effective_progs(struct cgroup *cgrp,
 					    &p->bpf.progs[type], node) {
 				if (!pl->prog)
 					continue;
-				rcu_dereference_protected(progs, 1)->
-					progs[cnt++] = pl->prog;
+				progs->progs[cnt++] = pl->prog;
 			}
 		p = cgroup_parent(p);
 	} while (p);
 
-	*array = progs;
+	rcu_assign_pointer(*array, progs);
 	return 0;
 }
 
-- 
2.17.1