[PATCH] PCI/sysfs: off by two and memory corruption in driver_override parameter

[PATCH] PCI/sysfs: off by two and memory corruption in driver_override parameter

[Sasha Levin]

There are two different issues fixed here:

 - On nun-NULL terminated input a random byte of memory would get flipped
from '\n' to '\0'.
 - When printing the driver_override parameter when it is 4095 and 4094 bytes
long the printing code would access invalid memory.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 drivers/pci/pci-sysfs.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index aa012fb..be6b2b1 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -521,17 +521,17 @@ static ssize_t driver_override_store(struct device *dev,
 	struct pci_dev *pdev = to_pci_dev(dev);
 	char *driver_override, *old = pdev->driver_override, *cp;
 
-	if (count > PATH_MAX)
+	/* We need to keep extra room for a newline */
+	if (count >= (PATH_MAX - 1))
 		return -EINVAL;
 
 	driver_override = kstrndup(buf, count, GFP_KERNEL);
 	if (!driver_override)
 		return -ENOMEM;
 
-	cp = strchr(driver_override, '\n');
-	if (cp)
-		*cp = '\0';
-
+	driver_override[count] = '\0';
+	if (driver_override[count - 1] == '\n')
+		driver_override[count - 1] = 0;
 	if (strlen(driver_override)) {
 		pdev->driver_override = driver_override;
 	} else {
-- 
1.7.10.4

Re: [PATCH] PCI/sysfs: off by two and memory corruption in driver_override parameter

[Bjorn Helgaas]

On Thu, Jan 1, 2015 at 5:27 PM, Sasha Levin <sasha.levin@oracle.com> wrote:
> There are two different issues fixed here:
>
>  - On nun-NULL terminated input a random byte of memory would get flipped
> from '\n' to '\0'.
>  - When printing the driver_override parameter when it is 4095 and 4094 bytes
> long the printing code would access invalid memory.

Thanks, Sasha.

Can you please:

  - Split these two fixes into two separate patches
  - Look up the commit that introduced this code
  - CC the author
  - Add "Fixes: " lines
  - Add stable tags for the relevant kernels

Bjorn

> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
> ---
>  drivers/pci/pci-sysfs.c |   10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index aa012fb..be6b2b1 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -521,17 +521,17 @@ static ssize_t driver_override_store(struct device *dev,
>         struct pci_dev *pdev = to_pci_dev(dev);
>         char *driver_override, *old = pdev->driver_override, *cp;
>
> -       if (count > PATH_MAX)
> +       /* We need to keep extra room for a newline */
> +       if (count >= (PATH_MAX - 1))
>                 return -EINVAL;
>
>         driver_override = kstrndup(buf, count, GFP_KERNEL);
>         if (!driver_override)
>                 return -ENOMEM;
>
> -       cp = strchr(driver_override, '\n');
> -       if (cp)
> -               *cp = '\0';
> -
> +       driver_override[count] = '\0';
> +       if (driver_override[count - 1] == '\n')
> +               driver_override[count - 1] = 0;
>         if (strlen(driver_override)) {
>                 pdev->driver_override = driver_override;
>         } else {
> --
> 1.7.10.4
>