[PATCH] drivers/md/md.c: use kzalloc() when bitmap is disabled

[PATCH] drivers/md/md.c: use kzalloc() when bitmap is disabled

[Benjamin Randazzo]

In drivers/md/md.c get_bitmap_file() uses kmalloc() for creating a
mdu_bitmap_file_t called "file".

5769         file = kmalloc(sizeof(*file), GFP_NOIO);
5770         if (!file)
5771                 return -ENOMEM;

This structure is copied to user space at the end of the function.

5786         if (err == 0 &&
5787             copy_to_user(arg, file, sizeof(*file)))
5788                 err = -EFAULT

But if bitmap is disabled only the first byte of "file" is initialized
with zero, so it's possible to read some bytes (up to 4095) of kernel
space memory from user space. This is an information leak.

5775         /* bitmap disabled, zero the first byte and copy out */
5776         if (!mddev->bitmap_info.file)
5777                 file->pathname[0] = '\0';

Signed-off-by: Benjamin Randazzo <benjamin@randazzo.fr>
---
 drivers/md/md.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 80879dc..382bdbc 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5766,22 +5766,21 @@ static int get_bitmap_file(struct mddev *mddev, void __user * arg)
 	char *ptr;
 	int err;
 
-	file = kmalloc(sizeof(*file), GFP_NOIO);
+	file = kzalloc(sizeof(*file), GFP_NOIO);
 	if (!file)
 		return -ENOMEM;
 
 	err = 0;
 	spin_lock(&mddev->lock);
-	/* bitmap disabled, zero the first byte and copy out */
-	if (!mddev->bitmap_info.file)
-		file->pathname[0] = '\0';
-	else if ((ptr = file_path(mddev->bitmap_info.file,
-			       file->pathname, sizeof(file->pathname))),
-		 IS_ERR(ptr))
-		err = PTR_ERR(ptr);
-	else
-		memmove(file->pathname, ptr,
-			sizeof(file->pathname)-(ptr-file->pathname));
+	/* bitmap enabled */
+	if (mddev->bitmap_info.file) {
+		if ((ptr = file_path(mddev->bitmap_info.file, file->pathname,
+					sizeof(file->pathname))), IS_ERR(ptr))
+			err = PTR_ERR(ptr);
+		else
+			memmove(file->pathname, ptr,
+				sizeof(file->pathname)-(ptr-file->pathname));
+	}
 	spin_unlock(&mddev->lock);
 
 	if (err == 0 &&
-- 
2.3.6

Re: [PATCH] drivers/md/md.c: use kzalloc() when bitmap is disabled

[NeilBrown]

On Sat, 25 Jul 2015 16:36:50 +0200 Benjamin Randazzo
<benjamin@randazzo.fr> wrote:

> In drivers/md/md.c get_bitmap_file() uses kmalloc() for creating a
> mdu_bitmap_file_t called "file".
> 
> 5769         file = kmalloc(sizeof(*file), GFP_NOIO);
> 5770         if (!file)
> 5771                 return -ENOMEM;
> 
> This structure is copied to user space at the end of the function.
> 
> 5786         if (err == 0 &&
> 5787             copy_to_user(arg, file, sizeof(*file)))
> 5788                 err = -EFAULT
> 
> But if bitmap is disabled only the first byte of "file" is initialized
> with zero, so it's possible to read some bytes (up to 4095) of kernel
> space memory from user space. This is an information leak.
> 
> 5775         /* bitmap disabled, zero the first byte and copy out */
> 5776         if (!mddev->bitmap_info.file)
> 5777                 file->pathname[0] = '\0';
> 
> Signed-off-by: Benjamin Randazzo <benjamin@randazzo.fr>
> ---
>  drivers/md/md.c | 21 ++++++++++-----------
>  1 file changed, 10 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 80879dc..382bdbc 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -5766,22 +5766,21 @@ static int get_bitmap_file(struct mddev *mddev, void __user * arg)
>  	char *ptr;
>  	int err;
>  
> -	file = kmalloc(sizeof(*file), GFP_NOIO);
> +	file = kzalloc(sizeof(*file), GFP_NOIO);
>  	if (!file)
>  		return -ENOMEM;
>  
>  	err = 0;
>  	spin_lock(&mddev->lock);
> -	/* bitmap disabled, zero the first byte and copy out */
> -	if (!mddev->bitmap_info.file)
> -		file->pathname[0] = '\0';
> -	else if ((ptr = file_path(mddev->bitmap_info.file,
> -			       file->pathname, sizeof(file->pathname))),
> -		 IS_ERR(ptr))
> -		err = PTR_ERR(ptr);
> -	else
> -		memmove(file->pathname, ptr,
> -			sizeof(file->pathname)-(ptr-file->pathname));
> +	/* bitmap enabled */
> +	if (mddev->bitmap_info.file) {
> +		if ((ptr = file_path(mddev->bitmap_info.file, file->pathname,
> +					sizeof(file->pathname))), IS_ERR(ptr))
> +			err = PTR_ERR(ptr);
> +		else
> +			memmove(file->pathname, ptr,
> +				sizeof(file->pathname)-(ptr-file->pathname));
> +	}
>  	spin_unlock(&mddev->lock);
>  
>  	if (err == 0 &&


Thanks.
I re-arranged the code a little bit more as there is no longer any
excuse for having the "ptr = file_path()" assignment inside the
condition of the 'if'.

Applied.  Thanks,
NeilBrown