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[85.204.121.218]) by smtp.gmail.com with ESMTPSA id t21sm1364896ejs.37.2019.09.08.01.20.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 08 Sep 2019 01:20:46 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 0F739180615; Sun, 8 Sep 2019 09:20:44 +0100 (WEST) From: =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= To: make-wifi-fast@lists.bufferbloat.net, linux-wireless@vger.kernel.org, ast@kernel.org, bpf@vger.kernel.org, daniel@iogearbox.net, davem@davemloft.net, hawk@kernel.org, jakub.kicinski@netronome.com, john.fastabend@gmail.com, kafai@fb.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, songliubraving@fb.com, syzkaller-bugs@googlegroups.com, yhs@fb.com Cc: =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= , syzbot+4e7a85b1432052e8d6f8@syzkaller.appspotmail.com Subject: [PATCH bpf-next] xdp: Fix race in dev_map_hash_update_elem() when replacing element Date: Sun, 8 Sep 2019 09:20:16 +0100 Message-Id: <20190908082016.17214-1-toke@redhat.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <0000000000005091a70591d3e1d9@google.com> References: <0000000000005091a70591d3e1d9@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org syzbot found a crash in dev_map_hash_update_elem(), when replacing an element with a new one. Jesper correctly identified the cause of the crash as a race condition between the initial lookup in the map (which is done before taking the lock), and the removal of the old element. Rather than just add a second lookup into the hashmap after taking the lock, fix this by reworking the function logic to take the lock before the initial lookup. Fixes: 6f9d451ab1a3 ("xdp: Add devmap_hash map type for looking up devices by hashed index") Reported-and-tested-by: syzbot+4e7a85b1432052e8d6f8@syzkaller.appspotmail.com Signed-off-by: Toke Høiland-Jørgensen --- kernel/bpf/devmap.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c index 9af048a932b5..d27f3b60ff6d 100644 --- a/kernel/bpf/devmap.c +++ b/kernel/bpf/devmap.c @@ -650,19 +650,22 @@ static int __dev_map_hash_update_elem(struct net *net, struct bpf_map *map, u32 ifindex = *(u32 *)value; u32 idx = *(u32 *)key; unsigned long flags; + int err = -EEXIST; if (unlikely(map_flags > BPF_EXIST || !ifindex)) return -EINVAL; + spin_lock_irqsave(&dtab->index_lock, flags); + old_dev = __dev_map_hash_lookup_elem(map, idx); if (old_dev && (map_flags & BPF_NOEXIST)) - return -EEXIST; + goto out_err; dev = __dev_map_alloc_node(net, dtab, ifindex, idx); - if (IS_ERR(dev)) - return PTR_ERR(dev); - - spin_lock_irqsave(&dtab->index_lock, flags); + if (IS_ERR(dev)) { + err = PTR_ERR(dev); + goto out_err; + } if (old_dev) { hlist_del_rcu(&old_dev->index_hlist); @@ -683,6 +686,10 @@ static int __dev_map_hash_update_elem(struct net *net, struct bpf_map *map, call_rcu(&old_dev->rcu, __dev_map_entry_free); return 0; + +out_err: + spin_unlock_irqrestore(&dtab->index_lock, flags); + return err; } static int dev_map_hash_update_elem(struct bpf_map *map, void *key, void *value, -- 2.23.0