Re: [PATCH v4 6/6] btrfs: use btrfs_get_dev_args_from_path in dev removal ioctls

[Nikolay Borisov <nborisov@suse.com>]

On 6.10.21 г. 11:54, Anand Jain wrote:
<snip>

>> Suggested-by: Anand Jain <anand.jain@oracle.com>
>> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
>> ---
>>   fs/btrfs/ioctl.c   | 67 +++++++++++++++++++++++++++-------------------
>>   fs/btrfs/volumes.c | 15 +++++------
>>   fs/btrfs/volumes.h |  2 +-
>>   3 files changed, 48 insertions(+), 36 deletions(-)
>>
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>> index b8508af4e539..c9d3f375df83 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -3160,6 +3160,7 @@ static long btrfs_ioctl_add_dev(struct
>> btrfs_fs_info *fs_info, void __user *arg)
>>     static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user
>> *arg)
>>   {
>> +    BTRFS_DEV_LOOKUP_ARGS(args);
>>       struct inode *inode = file_inode(file);
>>       struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
>>       struct btrfs_ioctl_vol_args_v2 *vol_args;
>> @@ -3171,35 +3172,39 @@ static long btrfs_ioctl_rm_dev_v2(struct file
>> *file, void __user *arg)
>>       if (!capable(CAP_SYS_ADMIN))
>>           return -EPERM;
>>   -    ret = mnt_want_write_file(file);
>> -    if (ret)
>> -        return ret;
>> -
>>       vol_args = memdup_user(arg, sizeof(*vol_args));
>>       if (IS_ERR(vol_args)) {
> 
>>           ret = PTR_ERR(vol_args);
>> -        goto err_drop;
>> +        goto out;
> 
>      return  PTR_ERR(vol_args);
> 
> is fine here.
> 
>>       }
>>         if (vol_args->flags & ~BTRFS_DEVICE_REMOVE_ARGS_MASK) {
>>           ret = -EOPNOTSUPP;
>>           goto out;
> 
> At the label out, we call, btrfs_put_dev_args_from_path(&args).
> However, the args.fsid and args.uuid might not have initialized
> to NULL or a valid kmem address.

On tha contrary, the fact that args is initialized via a designated
initializer guarantees that the rest of the members of the struct are
going to be zero initialized, or more precisley as if they had a "static
lifetime"

https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html

<snip>