Re: [RFC PATCH net-next] ipvs: add missing lock in ip_vs_ftp_init_conn()

[Simon Horman <horms@verge.net.au>]

On Tue, Jul 03, 2012 at 10:12:41AM +0300, Julian Anastasov wrote:
> 
> 	Hello,
> 
> On Thu, 28 Jun 2012, Xiaotian Feng wrote:
> 
> > We met a kernel panic in 2.6.32.43 kernel:
> > 
> > [2680191.848044] IPVS: ip_vs_conn_hash(): request for already hashed, called from run_timer_softirq+0x175/0x1d0
> > <snip>
> > [2680311.849009] general protection fault: 0000 [#1] SMP
> > [2680311.853001] RIP: 0010:[<ffffffff815f155c>]  [<ffffffff815f155c>] ip_vs_conn_expire+0xdc/0x2f0
> > [2680311.853001] RSP: 0018:ffff880028303e70  EFLAGS: 00010202
> > [2680311.853001] RAX: dead000000200200 RBX: ffff8801aad00b80 RCX: 0000000000001d90
> > [2680311.853001] RDX: dead000000100100 RSI: 000000004fd59800 RDI: ffff8801aad00c08
> > <snip>
> > [2680311.853001] Call Trace:
> > [2680311.853001]  <IRQ>
> > [2680311.853001]  [<ffffffff815f1480>] ? ip_vs_conn_expire+0x0/0x2f0
> > [2680311.853001]  [<ffffffff8104e2a5>] run_timer_softirq+0x175/0x1d0
> > [2680311.853001]  [<ffffffff81021a48>] ? lapic_next_event+0x18/0x20
> > [2680311.853001]  [<ffffffff81049a13>] __do_softirq+0xb3/0x150
> > [2680311.853001]  [<ffffffff8100cc5c>] call_softirq+0x1c/0x30
> > [2680311.853001]  [<ffffffff8100ea9a>] do_softirq+0x4a/0x80
> > [2680311.853001]  [<ffffffff81049957>] irq_exit+0x77/0x80
> > [2680311.853001]  [<ffffffff81021f2c>] smp_apic_timer_interrupt+0x6c/0xa0
> > [2680311.853001]  [<ffffffff8100c633>] apic_timer_interrupt+0x13/0x20
> > [2680311.853001]  <EOI>
> > [2680311.853001]  [<ffffffff81013b52>] ? mwait_idle+0x52/0x70
> > [2680311.853001]  [<ffffffff8100a7b0>] ? enter_idle+0x20/0x30
> > [2680311.853001]  [<ffffffff8100ac62>] ? cpu_idle+0x52/0x80
> > [2680311.853001]  [<ffffffff816d504d>] ? start_secondary+0x19d/0x280
> > 
> > rax and rdx is LIST_POISON1 and LIST_POISON2, so kernel is list_del() on an already deleted
> > connection and result the general protect fault.
> > 
> > The "request for already hashed" warning, told us someone might change the connection flags
> > incorrectly, like described in commit aea9d711, it changes the connection flags, but doesn't
> > put the connection back to the list. So ip_vs_conn_hash() throw a warning and return.
> > Later, when ip_vs_conn_expire fire again, ip_vs_conn_unhash() will find the HASHED connection
> > and list_del() it, then kernel panic happened.
> > 
> > After code review, the only chance that kernel change connection flag without protection is
> > in ip_vs_ftp_init_conn().
> > 
> > Signed-off-by: Xiaotian Feng <dannyfeng@tencent.com>
> > Cc: Wensong Zhang <wensong@linux-vs.org>
> > Cc: Simon Horman <horms@verge.net.au>
> > Cc: Julian Anastasov <ja@ssi.bg>
> > Cc: Pablo Neira Ayuso <pablo@netfilter.org>
> > Cc: Patrick McHardy <kaber@trash.net>
> > Cc: "David S. Miller" <davem@davemloft.net> 
> 
> 	For the fix below:
> 
> Acked-by: Julian Anastasov <ja@ssi.bg>
> 
> 	Simon, the change looks ok. ip_vs_ftp_init_conn is called
> from context where cp->lock is not locked (no double lock), so it
> should be safe for the backup.
> 
> 	Only that the comment is not specifying that we
> fix a problem in the backup server.

Thanks.

I have pushed this to my ipvs branch and will see about getting it included in 3.5.

It appears that this problem has been present since (at least) 2.6.37 and
my feeling is that it is -stable material.