* [PATCH][serial-next] serial: 8250: don't dereference em485 until it has been null checked
@ 2017-08-29 16:58 Colin King
2017-08-29 19:57 ` Andy Shevchenko
2017-08-29 20:04 ` Dan Carpenter
0 siblings, 2 replies; 4+ messages in thread
From: Colin King @ 2017-08-29 16:58 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby, Andy Shevchenko, Phil Elwell,
Jan Kiszka, Eric Anholt, Thor Thayer, Rafael Gago, David Lechner,
linux-serial
Cc: kernel-janitors, linux-kernel
From: Colin Ian King <colin.king@canonical.com>
Currently, the pointer em485 is dereferenced to get p and then later
em485 is checked to see if it is null before calling __start_tx. In
the case where em485 is null, we get a null pointer dereference. Fix
this by moving the deference and the associated spinlock/unlocks on
p to the code block where em485 is known to be not null.
Detected by CoverityScan, CID#14555001 ("Dereference before null check")
Fixes 6e0a5de2136b ("serial: 8250: Use hrtimers for rs485 delays")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
drivers/tty/serial/8250/8250_port.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 4726aa276968..c20b581313f0 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1606,18 +1606,18 @@ static inline void start_tx_rs485(struct uart_port *port)
static enum hrtimer_restart serial8250_em485_handle_start_tx(struct hrtimer *t)
{
struct uart_8250_em485 *em485;
- struct uart_8250_port *p;
unsigned long flags;
em485 = container_of(t, struct uart_8250_em485, start_tx_timer);
- p = em485->port;
- spin_lock_irqsave(&p->port.lock, flags);
if (em485 &&
em485->active_timer == &em485->start_tx_timer) {
+ struct uart_8250_port *p = em485->port;
+
+ spin_lock_irqsave(&p->port.lock, flags);
__start_tx(&p->port);
em485->active_timer = NULL;
+ spin_unlock_irqrestore(&p->port.lock, flags);
}
- spin_unlock_irqrestore(&p->port.lock, flags);
return HRTIMER_NORESTART;
}
--
2.14.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH][serial-next] serial: 8250: don't dereference em485 until it has been null checked
2017-08-29 16:58 [PATCH][serial-next] serial: 8250: don't dereference em485 until it has been null checked Colin King
@ 2017-08-29 19:57 ` Andy Shevchenko
2017-08-29 20:04 ` Dan Carpenter
1 sibling, 0 replies; 4+ messages in thread
From: Andy Shevchenko @ 2017-08-29 19:57 UTC (permalink / raw)
To: Colin King, Greg Kroah-Hartman, Jiri Slaby, Phil Elwell,
Jan Kiszka, Eric Anholt, Thor Thayer, Rafael Gago, David Lechner,
linux-serial
Cc: kernel-janitors, linux-kernel
On Tue, 2017-08-29 at 17:58 +0100, Colin King wrote:
> Currently, the pointer em485 is dereferenced to get p and then later
> em485 is checked to see if it is null before calling __start_tx. In
> the case where em485 is null, we get a null pointer dereference. Fix
> this by moving the deference and the associated spinlock/unlocks on
> p to the code block where em485 is known to be not null.
> static enum hrtimer_restart serial8250_em485_handle_start_tx(struct
> hrtimer *t)
> {
> struct uart_8250_em485 *em485;
> - struct uart_8250_port *p;
> unsigned long flags;
> em485 = container_of(t, struct uart_8250_em485,
> start_tx_timer);
> - p = em485->port;
>
> - spin_lock_irqsave(&p->port.lock, flags);
> if (em485 &&
> em485->active_timer == &em485->start_tx_timer) {
> + struct uart_8250_port *p = em485->port;
> +
> + spin_lock_irqsave(&p->port.lock, flags);
Can you describe, please, what on your opinion is protected by this
lock?
> __start_tx(&p->port);
> em485->active_timer = NULL;
> + spin_unlock_irqrestore(&p->port.lock, flags);
> }
> - spin_unlock_irqrestore(&p->port.lock, flags);
> return HRTIMER_NORESTART;
> }
>
--
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH][serial-next] serial: 8250: don't dereference em485 until it has been null checked
2017-08-29 16:58 [PATCH][serial-next] serial: 8250: don't dereference em485 until it has been null checked Colin King
2017-08-29 19:57 ` Andy Shevchenko
@ 2017-08-29 20:04 ` Dan Carpenter
2017-08-29 20:22 ` Andy Shevchenko
1 sibling, 1 reply; 4+ messages in thread
From: Dan Carpenter @ 2017-08-29 20:04 UTC (permalink / raw)
To: Colin King
Cc: Greg Kroah-Hartman, Jiri Slaby, Andy Shevchenko, Phil Elwell,
Jan Kiszka, Eric Anholt, Thor Thayer, Rafael Gago, David Lechner,
linux-serial, kernel-janitors, linux-kernel
On Tue, Aug 29, 2017 at 05:58:15PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
>
> Currently, the pointer em485 is dereferenced to get p and then later
> em485 is checked to see if it is null before calling __start_tx. In
> the case where em485 is null, we get a null pointer dereference. Fix
> this by moving the deference and the associated spinlock/unlocks on
> p to the code block where em485 is known to be not null.
>
> Detected by CoverityScan, CID#14555001 ("Dereference before null check")
>
> Fixes 6e0a5de2136b ("serial: 8250: Use hrtimers for rs485 delays")
I don't understand which tree this commit is from. I have it fetched
but when I do a git log on drivers/tty/serial/8250/8250_port.c then I
don't see it. I have today's linux-next.
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
> drivers/tty/serial/8250/8250_port.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 4726aa276968..c20b581313f0 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -1606,18 +1606,18 @@ static inline void start_tx_rs485(struct uart_port *port)
> static enum hrtimer_restart serial8250_em485_handle_start_tx(struct hrtimer *t)
I'm pretty sure "t" isn't ever NULL.
regards,
dan carpenter
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH][serial-next] serial: 8250: don't dereference em485 until it has been null checked
2017-08-29 20:04 ` Dan Carpenter
@ 2017-08-29 20:22 ` Andy Shevchenko
0 siblings, 0 replies; 4+ messages in thread
From: Andy Shevchenko @ 2017-08-29 20:22 UTC (permalink / raw)
To: Dan Carpenter, Colin King
Cc: Greg Kroah-Hartman, Jiri Slaby, Phil Elwell, Jan Kiszka,
Eric Anholt, Thor Thayer, Rafael Gago, David Lechner,
linux-serial, kernel-janitors, linux-kernel
On Tue, 2017-08-29 at 23:04 +0300, Dan Carpenter wrote:
> On Tue, Aug 29, 2017 at 05:58:15PM +0100, Colin King wrote:
> > From: Colin Ian King <colin.king@canonical.com>
> >
> > Currently, the pointer em485 is dereferenced to get p and then later
> > em485 is checked to see if it is null before calling __start_tx. In
> > the case where em485 is null, we get a null pointer dereference. Fix
> > this by moving the deference and the associated spinlock/unlocks on
> > p to the code block where em485 is known to be not null.
> >
> > Detected by CoverityScan, CID#14555001 ("Dereference before null
> > check")
> >
> > Fixes 6e0a5de2136b ("serial: 8250: Use hrtimers for rs485 delays")
>
> I don't understand which tree this commit is from. I have it fetched
> but when I do a git log on drivers/tty/serial/8250/8250_port.c then I
> don't see it. I have today's linux-next.
I see it, though I have tty-next as well.
> I'm pretty sure "t" isn't ever NULL.
(I'm pretty sure there is a false positive, though code would be cleaned
to avoid such reports)
--
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy
^ permalink raw reply [flat|nested] 4+ messages in thread
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2017-08-29 16:58 [PATCH][serial-next] serial: 8250: don't dereference em485 until it has been null checked Colin King
2017-08-29 19:57 ` Andy Shevchenko
2017-08-29 20:04 ` Dan Carpenter
2017-08-29 20:22 ` Andy Shevchenko
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