Re: [PATCH v2] fs/fcntl: restore checking against COMPAT_LOFF_T_MAX for F_GETLK64

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2017-11-14 at 16:47 +0300, Vitaly Lipatov wrote:
> for fcntl64 with F_GETLK64 we need use checking against COMPAT_LOFF_T_MAX.
> 
> Fixes: 94073ad77fff2 "fs/locks: don't mess with the address limit in compat_fcntl64"
> 
> Signed-off-by: Vitaly Lipatov <lav@etersoft.ru>
> ---
>  fs/fcntl.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/fcntl.c b/fs/fcntl.c
> index 30f47d0..e9443d9 100644
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -590,17 +590,17 @@ convert_fcntl_cmd(unsigned int cmd)
>   * GETLK was successful and we need to return the data, but it needs to fit in
>   * the compat structure.
>   * l_start shouldn't be too big, unless the original start + end is greater than
> - * COMPAT_OFF_T_MAX, in which case the app was asking for trouble, so we return
> + * COMPAT_OFF_T_MAX/COMPAT_LOFF_T_MAX, in which case the app was asking for trouble, so we return
>   * -EOVERFLOW in that case.  l_len could be too big, in which case we just
>   * truncate it, and only allow the app to see that part of the conflicting lock
>   * that might make sense to it anyway
>   */
> -static int fixup_compat_flock(struct flock *flock)
> +static int fixup_compat_flock(struct flock *flock, loff_t off_t_max)
>  {
> -	if (flock->l_start > COMPAT_OFF_T_MAX)
> +	if (flock->l_start > off_t_max)
>  		return -EOVERFLOW;
> -	if (flock->l_len > COMPAT_OFF_T_MAX)
> -		flock->l_len = COMPAT_OFF_T_MAX;
> +	if (flock->l_len > off_t_max)
> +		flock->l_len = off_t_max;
>  	return 0;
>  }
>  
> @@ -631,7 +631,7 @@ COMPAT_SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
>  		err = fcntl_getlk(f.file, convert_fcntl_cmd(cmd), &flock);
>  		if (err)
>  			break;
> -		err = fixup_compat_flock(&flock);
> +		err = fixup_compat_flock(&flock, COMPAT_OFF_T_MAX);
>  		if (err)
>  			return err;
>  		err = put_compat_flock(&flock, compat_ptr(arg));
> @@ -644,7 +644,7 @@ COMPAT_SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
>  		err = fcntl_getlk(f.file, convert_fcntl_cmd(cmd), &flock);
>  		if (err)
>  			break;
> -		err = fixup_compat_flock(&flock);
> +		err = fixup_compat_flock(&flock, COMPAT_OFF_T_MAX);

I think you want COMPAT_LOFF_T_MAX here? In any case, I'm fine with the
first version, and just renaming the function. I'll plan to push that
one unless you have a reason that we should do it this way.

>  		if (err)
>  			return err;
>  		err = put_compat_flock64(&flock, compat_ptr(arg));

Thanks,
-- 
Jeff Layton <jlayton@kernel.org>