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    Subject[PATCH 4.15 109/146] netfilter: ipt_CLUSTERIP: fix a race condition of proc file creation
    Date
    4.15-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Cong Wang <xiyou.wangcong@gmail.com>

    commit b3e456fce9f51d6276e576d00271e2813c1b8b67 upstream.

    There is a race condition between clusterip_config_entry_put()
    and clusterip_config_init(), after we release the spinlock in
    clusterip_config_entry_put(), a new proc file with a same IP could
    be created immediately since it is already removed from the configs
    list, therefore it triggers this warning:

    ------------[ cut here ]------------
    proc_dir_entry 'ipt_CLUSTERIP/172.20.0.170' already registered
    WARNING: CPU: 1 PID: 4152 at fs/proc/generic.c:330 proc_register+0x2a4/0x370 fs/proc/generic.c:329
    Kernel panic - not syncing: panic_on_warn set ...

    As a quick fix, just move the proc_remove() inside the spinlock.

    Reported-by: <syzbot+03218bcdba6aa76441a3@syzkaller.appspotmail.com>
    Fixes: 6c5d5cfbe3c5 ("netfilter: ipt_CLUSTERIP: check duplicate config when initializing")
    Tested-by: Paolo Abeni <pabeni@redhat.com>
    Cc: Xin Long <lucien.xin@gmail.com>
    Cc: Pablo Neira Ayuso <pablo@netfilter.org>
    Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
    Reviewed-by: Xin Long <lucien.xin@gmail.com>
    Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/ipv4/netfilter/ipt_CLUSTERIP.c | 12 ++++++------
    1 file changed, 6 insertions(+), 6 deletions(-)

    --- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
    +++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
    @@ -107,12 +107,6 @@ clusterip_config_entry_put(struct net *n

    local_bh_disable();
    if (refcount_dec_and_lock(&c->entries, &cn->lock)) {
    - list_del_rcu(&c->list);
    - spin_unlock(&cn->lock);
    - local_bh_enable();
    -
    - unregister_netdevice_notifier(&c->notifier);
    -
    /* In case anyone still accesses the file, the open/close
    * functions are also incrementing the refcount on their own,
    * so it's safe to remove the entry even if it's in use. */
    @@ -120,6 +114,12 @@ clusterip_config_entry_put(struct net *n
    if (cn->procdir)
    proc_remove(c->pde);
    #endif
    + list_del_rcu(&c->list);
    + spin_unlock(&cn->lock);
    + local_bh_enable();
    +
    + unregister_netdevice_notifier(&c->notifier);
    +
    return;
    }
    local_bh_enable();

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