2004-04-02 01:46:11

by Ken Ashcraft

Subject: [CHECKER] Race condition in i2o_core.c

Looks like there is a race condition in i2o_core_reply involving the
variable "evt_in". Notice that the increment of evt_in is protected by the
lock, but the reads are not protected. It looks like "events" should also
be protected by the lock. If this is not a race condition, the increment
should not be inside the critical section.

Feedback is appreciated.

thanks,
Ken Ashcraft
-----------------------------------
/home/kash/interface/linux-2.6.3/drivers/message/i2o/i2o_core.c:264:i2o_core_reply:
ERROR:RACE: 264:264:Possible race condition on variable "evt_in", No locks
held on read on line 264, Locks {&i2o_evt_lock } held on write on line 268
[COUNTER=i2o_handler.reply] [fit=1] [fit_fn=1] [fn_ex=0] [fn_counter=1]
[ex=1] [counter=1] [z = -2.91998558035372] [fn-z = -4.35889894354067]

return;
}

if(m->function == I2O_CMD_UTIL_EVT_REGISTER)
{

Error --->
memcpy(events[evt_in].msg, msg, (msg[0]>>16)<<2);
events[evt_in].iop = c;

spin_lock(&i2o_evt_lock);
MODINC(evt_in, I2O_EVT_Q_LEN);
if(evt_q_len == I2O_EVT_Q_LEN)
MODINC(evt_out, I2O_EVT_Q_LEN);
else
evt_q_len++;
spin_unlock(&i2o_evt_lock);

up(&evt_sem);
wake_up_interruptible(&evt_wait);
return;

2004-04-02 02:12:35

by Randy.Dunlap

Subject: Re: [CHECKER] Race condition in i2o_core.c

On Thu, 01 Apr 2004 17:46:00 -0800 Ken Ashcraft wrote:

| Looks like there is a race condition in i2o_core_reply involving the
| variable "evt_in". Notice that the increment of evt_in is protected by the
| lock, but the reads are not protected. It looks like "events" should also
| be protected by the lock. If this is not a race condition, the increment
| should not be inside the critical section.
|
| Feedback is appreciated.
|
| thanks,
| Ken Ashcraft
| -----------------------------------
| /home/kash/interface/linux-2.6.3/drivers/message/i2o/i2o_core.c:264:i2o_core_reply:
| ERROR:RACE: 264:264:Possible race condition on variable "evt_in", No locks
| held on read on line 264, Locks {&i2o_evt_lock } held on write on line 268
| [COUNTER=i2o_handler.reply] [fit=1] [fit_fn=1] [fn_ex=0] [fn_counter=1]
| [ex=1] [counter=1] [z = -2.91998558035372] [fn-z = -4.35889894354067]
|
| return;
| }
|
| if(m->function == I2O_CMD_UTIL_EVT_REGISTER)
| {
|
| Error --->
| memcpy(events[evt_in].msg, msg, (msg[0]>>16)<<2);

static int evt_in;
Access to <int> is (considered to be) atomic.
However, the MODINC() macro is nowhere close to atomic.
Does that help?

| events[evt_in].iop = c;
|
| spin_lock(&i2o_evt_lock);
| MODINC(evt_in, I2O_EVT_Q_LEN);
| if(evt_q_len == I2O_EVT_Q_LEN)
| MODINC(evt_out, I2O_EVT_Q_LEN);
| else
| evt_q_len++;
| spin_unlock(&i2o_evt_lock);
|
| up(&evt_sem);
| wake_up_interruptible(&evt_wait);
| return;


--
~Randy
(Again. Sometimes I think ln -s /usr/src/linux/.config .signature)

2004-04-02 09:19:38

by Alan Cox

Subject: Re: [CHECKER] Race condition in i2o_core.c

On Thu, Apr 01, 2004 at 05:46:00PM -0800, Ken Ashcraft wrote:
> Looks like there is a race condition in i2o_core_reply involving the
> variable "evt_in". Notice that the increment of evt_in is protected by the
> lock, but the reads are not protected. It looks like "events" should also
> be protected by the lock. If this is not a race condition, the increment
> should not be inside the critical section.
>
> Feedback is appreciated.

Looks a fair catch to me.