[PATCH] Btrfs: ensure path name is null terminated at btrfs_control_ioctl

[PATCH] Btrfs: ensure path name is null terminated at btrfs_control_ioctl

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

We were using the path name received from user space without checking that
it is null terminated. While btrfs-progs is well behaved and does proper
validation and null termination, someone could call the ioctl and pass
a non-null terminated patch, leading to buffer overrun problems in the
kernel.

So just set the last byte of the path to a null character, similar to what
we do in other ioctls (add/remove/resize device, snapshot creation, etc).

Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/super.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 6601c9aa5e35..8ad145820ea8 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2235,6 +2235,7 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
 	vol = memdup_user((void __user *)arg, sizeof(*vol));
 	if (IS_ERR(vol))
 		return PTR_ERR(vol);
+	vol->name[BTRFS_PATH_NAME_MAX] = '\0';
 
 	switch (cmd) {
 	case BTRFS_IOC_SCAN_DEV:
-- 
2.11.0

Re: [PATCH] Btrfs: ensure path name is null terminated at btrfs_control_ioctl

[Anand Jain]

On 11/14/2018 07:35 PM, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> We were using the path name received from user space without checking that
> it is null terminated. While btrfs-progs is well behaved and does proper
> validation and null termination, someone could call the ioctl and pass
> a non-null terminated patch, leading to buffer overrun problems in the
> kernel.
> 
> So just set the last byte of the path to a null character, similar to what
> we do in other ioctls (add/remove/resize device, snapshot creation, etc).
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

  Reviewed-by: Anand Jain <anand.jain@oracle.com>

Thanks, Anand

> ---
>   fs/btrfs/super.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 6601c9aa5e35..8ad145820ea8 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -2235,6 +2235,7 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
>   	vol = memdup_user((void __user *)arg, sizeof(*vol));
>   	if (IS_ERR(vol))
>   		return PTR_ERR(vol);
> +	vol->name[BTRFS_PATH_NAME_MAX] = '\0';
>   
>   	switch (cmd) {
>   	case BTRFS_IOC_SCAN_DEV:
> 

Re: [PATCH] Btrfs: ensure path name is null terminated at btrfs_control_ioctl

[David Sterba]

On Wed, Nov 14, 2018 at 11:35:24AM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> We were using the path name received from user space without checking that
> it is null terminated. While btrfs-progs is well behaved and does proper
> validation and null termination, someone could call the ioctl and pass
> a non-null terminated patch, leading to buffer overrun problems in the
> kernel.
> 
> So just set the last byte of the path to a null character, similar to what
> we do in other ioctls (add/remove/resize device, snapshot creation, etc).
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Good catch, thanks

Reviewed-by: David Sterba <dsterba@suse.com>