* [PATCH] driver core: platform: fix race condition with driver_override
@ 2017-04-25 23:55 Adrian Salido
2017-04-26 11:57 ` Greg KH
0 siblings, 1 reply; 4+ messages in thread
From: Adrian Salido @ 2017-04-25 23:55 UTC (permalink / raw)
To: linux-kernel; +Cc: gregkh
The driver_override implementation is susceptible to race condition when
different threads are reading vs storing a different driver override.
Add locking to avoid race condition.
Fixes: 3d713e0e382e ("driver core: platform: add device binding path 'driver_override'")
Cc: stable@vger.kernel.org
Signed-off-by: Adrian Salido <salidoa@google.com>
---
drivers/base/platform.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index c2456839214a..493e03fa0e07 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -866,7 +866,7 @@ static ssize_t driver_override_store(struct device *dev,
const char *buf, size_t count)
{
struct platform_device *pdev = to_platform_device(dev);
- char *driver_override, *old = pdev->driver_override, *cp;
+ char *driver_override, *old, *cp;
if (count > PATH_MAX)
return -EINVAL;
@@ -879,12 +879,15 @@ static ssize_t driver_override_store(struct device *dev,
if (cp)
*cp = '\0';
+ device_lock(dev);
+ old = pdev->driver_override;
if (strlen(driver_override)) {
pdev->driver_override = driver_override;
} else {
kfree(driver_override);
pdev->driver_override = NULL;
}
+ device_unlock(dev);
kfree(old);
@@ -895,8 +898,12 @@ static ssize_t driver_override_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct platform_device *pdev = to_platform_device(dev);
+ ssize_t len;
- return sprintf(buf, "%s\n", pdev->driver_override);
+ device_lock(dev);
+ len = sprintf(buf, "%s\n", pdev->driver_override);
+ device_unlock(dev);
+ return len;
}
static DEVICE_ATTR_RW(driver_override);
--
2.13.0.rc0.306.g87b477812d-goog
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] driver core: platform: fix race condition with driver_override
2017-04-25 23:55 [PATCH] driver core: platform: fix race condition with driver_override Adrian Salido
@ 2017-04-26 11:57 ` Greg KH
2017-04-26 14:51 ` Adrian Salido
0 siblings, 1 reply; 4+ messages in thread
From: Greg KH @ 2017-04-26 11:57 UTC (permalink / raw)
To: Adrian Salido; +Cc: linux-kernel
On Tue, Apr 25, 2017 at 04:55:26PM -0700, Adrian Salido wrote:
> The driver_override implementation is susceptible to race condition when
> different threads are reading vs storing a different driver override.
> Add locking to avoid race condition.
>
> Fixes: 3d713e0e382e ("driver core: platform: add device binding path 'driver_override'")
> Cc: stable@vger.kernel.org
> Signed-off-by: Adrian Salido <salidoa@google.com>
> ---
> drivers/base/platform.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index c2456839214a..493e03fa0e07 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -866,7 +866,7 @@ static ssize_t driver_override_store(struct device *dev,
> const char *buf, size_t count)
> {
> struct platform_device *pdev = to_platform_device(dev);
> - char *driver_override, *old = pdev->driver_override, *cp;
> + char *driver_override, *old, *cp;
>
> if (count > PATH_MAX)
> return -EINVAL;
> @@ -879,12 +879,15 @@ static ssize_t driver_override_store(struct device *dev,
> if (cp)
> *cp = '\0';
>
> + device_lock(dev);
> + old = pdev->driver_override;
> if (strlen(driver_override)) {
> pdev->driver_override = driver_override;
> } else {
> kfree(driver_override);
> pdev->driver_override = NULL;
> }
> + device_unlock(dev);
>
> kfree(old);
Shouldn't you move the lock until after the kfree()? Or am I missing
what the lock is trying to protect here?
>
> @@ -895,8 +898,12 @@ static ssize_t driver_override_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> struct platform_device *pdev = to_platform_device(dev);
> + ssize_t len;
>
> - return sprintf(buf, "%s\n", pdev->driver_override);
> + device_lock(dev);
> + len = sprintf(buf, "%s\n", pdev->driver_override);
> + device_unlock(dev);
> + return len;
Why does the show function need to be changed at all? How can anything
"race" here?
thanks,
greg k-h
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] driver core: platform: fix race condition with driver_override
2017-04-26 11:57 ` Greg KH
@ 2017-04-26 14:51 ` Adrian Salido
2017-04-26 15:48 ` Greg KH
0 siblings, 1 reply; 4+ messages in thread
From: Adrian Salido @ 2017-04-26 14:51 UTC (permalink / raw)
To: Greg KH; +Cc: linux-kernel
> > The driver_override implementation is susceptible to race condition when
> > different threads are reading vs storing a different driver override.
> > Add locking to avoid race condition.
> >
> > Fixes: 3d713e0e382e ("driver core: platform: add device binding path 'driver_override'")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Adrian Salido <salidoa@google.com>
> > ---
> > drivers/base/platform.c | 11 +++++++++--
> > 1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> > index c2456839214a..493e03fa0e07 100644
> > --- a/drivers/base/platform.c
> > +++ b/drivers/base/platform.c
> > @@ -866,7 +866,7 @@ static ssize_t driver_override_store(struct device *dev,
> > const char *buf, size_t count)
> > {
> > struct platform_device *pdev = to_platform_device(dev);
> > - char *driver_override, *old = pdev->driver_override, *cp;
> > + char *driver_override, *old, *cp;
> >
> > if (count > PATH_MAX)
> > return -EINVAL;
> > @@ -879,12 +879,15 @@ static ssize_t driver_override_store(struct device *dev,
> > if (cp)
> > *cp = '\0';
> >
> > + device_lock(dev);
> > + old = pdev->driver_override;
> > if (strlen(driver_override)) {
> > pdev->driver_override = driver_override;
> > } else {
> > kfree(driver_override);
> > pdev->driver_override = NULL;
> > }
> > + device_unlock(dev);
> >
> > kfree(old);
>
> Shouldn't you move the lock until after the kfree()? Or am I missing
> what the lock is trying to protect here?
not really, the lock only protecting the variable
pdev->driver_override. Once the value has changed we no longer care
about "old" variable
> > if (cp)
> > *cp = '\0';
> >
> > + device_lock(dev);
> > + old = pdev->driver_override;
> > if (strlen(driver_override)) {
> > pdev->driver_override = driver_override;
> > } else {
> > kfree(driver_override);
> > pdev->driver_override = NULL;
> > }
> > + device_unlock(dev);
> >
> > kfree(old);
>
> >
> > @@ -895,8 +898,12 @@ static ssize_t driver_override_show(struct device *dev,
> > struct device_attribute *attr, char *buf)
> > {
> > struct platform_device *pdev = to_platform_device(dev);
> > + ssize_t len;
> >
> > - return sprintf(buf, "%s\n", pdev->driver_override);
> > + device_lock(dev);
> > + len = sprintf(buf, "%s\n", pdev->driver_override);
> > + device_unlock(dev);
> > + return len;
>
> Why does the show function need to be changed at all? How can anything
> "race" here?
The lock is trying to protect again race between store and show.
Suppose there are 2 threads:
Thread1:
while (1) {
driver_override_store("foo");
driver_override_store("");
}
Thread2:
while (1) driver_override_show();
Thread 1 | Thread 2
----------------------------------------|-----------------------
old = pdev->driver_override; |
| len = sprintf(buf,
"%s\n", pdev->driver_override);
| /* snprintf starts reading */
pdev->driver_override = |
driver_override; |
kfree(old); | /* use after free before
snprintf finishes execution */
Similarly there could be a race between multiple threads doing store
where memory leaks could happen
Thanks,
Adrian
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] driver core: platform: fix race condition with driver_override
2017-04-26 14:51 ` Adrian Salido
@ 2017-04-26 15:48 ` Greg KH
0 siblings, 0 replies; 4+ messages in thread
From: Greg KH @ 2017-04-26 15:48 UTC (permalink / raw)
To: Adrian Salido; +Cc: linux-kernel
On Wed, Apr 26, 2017 at 07:51:32AM -0700, Adrian Salido wrote:
> > > The driver_override implementation is susceptible to race condition when
> > > different threads are reading vs storing a different driver override.
> > > Add locking to avoid race condition.
> > >
> > > Fixes: 3d713e0e382e ("driver core: platform: add device binding path 'driver_override'")
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Adrian Salido <salidoa@google.com>
> > > ---
> > > drivers/base/platform.c | 11 +++++++++--
> > > 1 file changed, 9 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> > > index c2456839214a..493e03fa0e07 100644
> > > --- a/drivers/base/platform.c
> > > +++ b/drivers/base/platform.c
> > > @@ -866,7 +866,7 @@ static ssize_t driver_override_store(struct device *dev,
> > > const char *buf, size_t count)
> > > {
> > > struct platform_device *pdev = to_platform_device(dev);
> > > - char *driver_override, *old = pdev->driver_override, *cp;
> > > + char *driver_override, *old, *cp;
> > >
> > > if (count > PATH_MAX)
> > > return -EINVAL;
> > > @@ -879,12 +879,15 @@ static ssize_t driver_override_store(struct device *dev,
> > > if (cp)
> > > *cp = '\0';
> > >
> > > + device_lock(dev);
> > > + old = pdev->driver_override;
> > > if (strlen(driver_override)) {
> > > pdev->driver_override = driver_override;
> > > } else {
> > > kfree(driver_override);
> > > pdev->driver_override = NULL;
> > > }
> > > + device_unlock(dev);
> > >
> > > kfree(old);
> >
> > Shouldn't you move the lock until after the kfree()? Or am I missing
> > what the lock is trying to protect here?
>
> not really, the lock only protecting the variable
> pdev->driver_override. Once the value has changed we no longer care
> about "old" variable
What are you protecting it from? Being overwritten twice? Or something
else?
> > > if (cp)
> > > *cp = '\0';
> > >
> > > + device_lock(dev);
> > > + old = pdev->driver_override;
> > > if (strlen(driver_override)) {
> > > pdev->driver_override = driver_override;
> > > } else {
> > > kfree(driver_override);
> > > pdev->driver_override = NULL;
> > > }
> > > + device_unlock(dev);
> > >
> > > kfree(old);
> >
> > >
> > > @@ -895,8 +898,12 @@ static ssize_t driver_override_show(struct device *dev,
> > > struct device_attribute *attr, char *buf)
> > > {
> > > struct platform_device *pdev = to_platform_device(dev);
> > > + ssize_t len;
> > >
> > > - return sprintf(buf, "%s\n", pdev->driver_override);
> > > + device_lock(dev);
> > > + len = sprintf(buf, "%s\n", pdev->driver_override);
> > > + device_unlock(dev);
> > > + return len;
> >
> > Why does the show function need to be changed at all? How can anything
> > "race" here?
>
> The lock is trying to protect again race between store and show.
> Suppose there are 2 threads:
>
> Thread1:
> while (1) {
> driver_override_store("foo");
> driver_override_store("");
> }
>
> Thread2:
> while (1) driver_override_show();
>
> Thread 1 | Thread 2
> ----------------------------------------|-----------------------
> old = pdev->driver_override; |
> | len = sprintf(buf,
> "%s\n", pdev->driver_override);
> | /* snprintf starts reading */
> pdev->driver_override = |
> driver_override; |
> kfree(old); | /* use after free before
> snprintf finishes execution */
>
> Similarly there could be a race between multiple threads doing store
> where memory leaks could happen
Ah, the printing of the string, that makes more sense, thanks, I was
thinking of the assignment of the pointer itself, which is atomic on all
sane platforms.
As writing this is only allowed by root, it's not really a big deal,
I'll queue it up for the next release.
thanks,
greg k-h
^ permalink raw reply [flat|nested] 4+ messages in thread
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2017-04-25 23:55 [PATCH] driver core: platform: fix race condition with driver_override Adrian Salido
2017-04-26 11:57 ` Greg KH
2017-04-26 14:51 ` Adrian Salido
2017-04-26 15:48 ` Greg KH
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