[PATCH 1/2] thunderbolt: Fix a leak in tb_retimer_add()

[PATCH 1/2] thunderbolt: Fix a leak in tb_retimer_add()

[Dan Carpenter]

After the device_register() succeeds, then the correct way to clean up
is to call device_unregister().  The unregister calls both device_del()
and device_put().  Since this code was only device_del() it results in
a memory leak.

Fixes: dacb12877d92 ("thunderbolt: Add support for on-board retimers")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
This is from a new static checker warning.  Not tested.  With new
warnings it's also possible that I have misunderstood something
fundamental so review carefully etc.

 drivers/thunderbolt/retimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/thunderbolt/retimer.c b/drivers/thunderbolt/retimer.c
index 620bcf586ee2..7a5d61604c8b 100644
--- a/drivers/thunderbolt/retimer.c
+++ b/drivers/thunderbolt/retimer.c
@@ -347,7 +347,7 @@ static int tb_retimer_add(struct tb_port *port, u8 index, u32 auth_status)
 	ret = tb_retimer_nvm_add(rt);
 	if (ret) {
 		dev_err(&rt->dev, "failed to add NVM devices: %d\n", ret);
-		device_del(&rt->dev);
+		device_unregister(&rt->dev);
 		return ret;
 	}
 
-- 
2.30.2

[PATCH 2/2] thunderbolt: Fix off by one in tb_port_find_retimer()

[Dan Carpenter]

This array uses 1-based indexing so it corrupts memory one element
beyond of the array.  Fix it by making the array one element larger.

Fixes: dacb12877d92 ("thunderbolt: Add support for on-board retimers")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 drivers/thunderbolt/retimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/thunderbolt/retimer.c b/drivers/thunderbolt/retimer.c
index 7a5d61604c8b..c44fad2b9fbb 100644
--- a/drivers/thunderbolt/retimer.c
+++ b/drivers/thunderbolt/retimer.c
@@ -406,7 +406,7 @@ static struct tb_retimer *tb_port_find_retimer(struct tb_port *port, u8 index)
  */
 int tb_retimer_scan(struct tb_port *port)
 {
-	u32 status[TB_MAX_RETIMER_INDEX] = {};
+	u32 status[TB_MAX_RETIMER_INDEX + 1] = {};
 	int ret, i, last_idx = 0;
 
 	if (!port->cap_usb4)
-- 
2.30.2

Re: [PATCH 1/2] thunderbolt: Fix a leak in tb_retimer_add()

[Jason Gunthorpe]

On Mon, Mar 29, 2021 at 09:07:18AM +0300, Dan Carpenter wrote:
> After the device_register() succeeds, then the correct way to clean up
> is to call device_unregister().  The unregister calls both device_del()
> and device_put().  Since this code was only device_del() it results in
> a memory leak.
> 
> Fixes: dacb12877d92 ("thunderbolt: Add support for on-board retimers")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> This is from a new static checker warning.  Not tested.  With new
> warnings it's also possible that I have misunderstood something
> fundamental so review carefully etc.

It looks OK to me

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

This also highlights the code has an ordering issue too, it calls
device_register() then goes to do tb_retimer_nvm_add() however
device_register() makes sysfs attributes visible before the rt->nvm is
initialized and this:

static ssize_t nvm_authenticate_store(struct device *dev,
	struct device_attribute *attr, const char *buf, size_t count)
{
	if (!rt->nvm) {

Isn't strong enough to close the potential racing. The nvm should be
setup before device_register and all the above tests in the sysfs
deleted so we can rely on the CPU barriers built into
device_register() for correctness.

[which is a general tip, be very suspicious if device_register() is
being error unwound]

Jason

Re: [PATCH 1/2] thunderbolt: Fix a leak in tb_retimer_add()

[Mika Westerberg]

Hi,

On Mon, Mar 29, 2021 at 10:02:20AM -0300, Jason Gunthorpe wrote:
> On Mon, Mar 29, 2021 at 09:07:18AM +0300, Dan Carpenter wrote:
> > After the device_register() succeeds, then the correct way to clean up
> > is to call device_unregister().  The unregister calls both device_del()
> > and device_put().  Since this code was only device_del() it results in
> > a memory leak.
> > 
> > Fixes: dacb12877d92 ("thunderbolt: Add support for on-board retimers")
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> > This is from a new static checker warning.  Not tested.  With new
> > warnings it's also possible that I have misunderstood something
> > fundamental so review carefully etc.
> 
> It looks OK to me

I agree too.

> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Thanks for the review!

> This also highlights the code has an ordering issue too, it calls
> device_register() then goes to do tb_retimer_nvm_add() however
> device_register() makes sysfs attributes visible before the rt->nvm is
> initialized and this:
> 
> static ssize_t nvm_authenticate_store(struct device *dev,
> 	struct device_attribute *attr, const char *buf, size_t count)
> {
> 	if (!rt->nvm) {
> 
> Isn't strong enough to close the potential racing. The nvm should be
> setup before device_register and all the above tests in the sysfs
> deleted so we can rely on the CPU barriers built into
> device_register() for correctness.
> 
> [which is a general tip, be very suspicious if device_register() is
> being error unwound]

The nvm is a separate (physical Linux) device that gets added under this
one. It cannot be added before AFAICT.

The code you refer actually looks like this:

static ssize_t nvm_authenticate_store(struct device *dev,
 	struct device_attribute *attr, const char *buf, size_t count)
{
	...
        if (!mutex_trylock(&rt->tb->lock)) {
                ret = restart_syscall();
                goto exit_rpm;
        }

        if (!rt->nvm) {
                ret = -EAGAIN;
                goto exit_unlock;
        }


Idea here is that if the NVMem (nvm) is not yet registered the attribute is
there but we return -EAGAIN to the userspace.

Re: [PATCH 1/2] thunderbolt: Fix a leak in tb_retimer_add()

[Jason Gunthorpe]

On Mon, Mar 29, 2021 at 05:43:23PM +0300, Mika Westerberg wrote:

> The nvm is a separate (physical Linux) device that gets added under this
> one. It cannot be added before AFAICT.

Hum, yes, but then it is odd that a parent is holding sysfs attributes
that refer to a child.

> The code you refer actually looks like this:
> 
> static ssize_t nvm_authenticate_store(struct device *dev,
>  	struct device_attribute *attr, const char *buf, size_t count)
> {
> 	...
>         if (!mutex_trylock(&rt->tb->lock)) {
>                 ret = restart_syscall();
>                 goto exit_rpm;
>         }

Is that lock held during tb_retimer_nvm_add() I looked for a bit and
didn't find something. So someplace more than 4 call site above
mandatory locking is being held?

static void tb_retimer_remove(struct tb_retimer *rt)
{
	dev_info(&rt->dev, "retimer disconnected\n");
	tb_nvm_free(rt->nvm);
	device_unregister(&rt->dev);
}

Here too?

And this is why it is all trylock because it deadlocks with unregister
otherwise?

Jason

Re: [PATCH 1/2] thunderbolt: Fix a leak in tb_retimer_add()

[Mika Westerberg]

On Mon, Mar 29, 2021 at 11:54:05AM -0300, Jason Gunthorpe wrote:
> On Mon, Mar 29, 2021 at 05:43:23PM +0300, Mika Westerberg wrote:
> 
> > The nvm is a separate (physical Linux) device that gets added under this
> > one. It cannot be added before AFAICT.
> 
> Hum, yes, but then it is odd that a parent is holding sysfs attributes
> that refer to a child.

Well the child (NVMem) comes from completely different subsystem that
does not have a concept of "authentication" or anythin similar. This is
what we add on top. We actually exposer two NVMem devices under each
retimer: one that is the current active one, and then the one that is
used to write the new firmware image.

> > The code you refer actually looks like this:
> > 
> > static ssize_t nvm_authenticate_store(struct device *dev,
> >  	struct device_attribute *attr, const char *buf, size_t count)
> > {
> > 	...
> >         if (!mutex_trylock(&rt->tb->lock)) {
> >                 ret = restart_syscall();
> >                 goto exit_rpm;
> >         }
> 
> Is that lock held during tb_retimer_nvm_add() I looked for a bit and
> didn't find something. So someplace more than 4 call site above
> mandatory locking is being held?

Yes it is. It is called from tb_scan_port() where that lock is held.

> static void tb_retimer_remove(struct tb_retimer *rt)
> {
> 	dev_info(&rt->dev, "retimer disconnected\n");
> 	tb_nvm_free(rt->nvm);
> 	device_unregister(&rt->dev);
> }
> 
> Here too?

Yes.

> And this is why it is all trylock because it deadlocks with unregister
> otherwise?

I tried to explain it in 09f11b6c99fe ("thunderbolt: Take domain lock in
switch sysfs attribute callbacks"), except that at that time we did not
have retimers exposed but the same applies here too.

Re: [PATCH 1/2] thunderbolt: Fix a leak in tb_retimer_add()

[Mika Westerberg]

On Mon, Mar 29, 2021 at 09:07:18AM +0300, Dan Carpenter wrote:
> After the device_register() succeeds, then the correct way to clean up
> is to call device_unregister().  The unregister calls both device_del()
> and device_put().  Since this code was only device_del() it results in
> a memory leak.
> 
> Fixes: dacb12877d92 ("thunderbolt: Add support for on-board retimers")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> This is from a new static checker warning.  Not tested.  With new
> warnings it's also possible that I have misunderstood something
> fundamental so review carefully etc.
> 
>  drivers/thunderbolt/retimer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Both patches applied to thunderbolt.git/fixes. Thanks Dan!