Re: [PATCH 2/2] fs/locks: don't mess with the address limit in compat_fcntl64

[Jeff Layton <jlayton@poochiereds.net>]

On Mon, 2017-05-15 at 22:33 +0200, Christoph Hellwig wrote:
> Instead write a proper compat syscall that calls common helpers.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/fcntl.c | 118 +++++++++++++++++++++++++++++++++++--------------------------
>  fs/locks.c |   2 +-
>  2 files changed, 68 insertions(+), 52 deletions(-)
> 
> diff --git a/fs/fcntl.c b/fs/fcntl.c
> index 671ac43c65df..9d909b029063 100644
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -505,76 +505,92 @@ convert_fcntl_cmd(unsigned int cmd)
>  	return 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
> + * -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)
> +{
> +	if (flock.l_start > COMPAT_OFF_T_MAX)
> +		return -EOVERFLOW;
> +	if (flock.l_len > COMPAT_OFF_T_MAX)
> +		flock.l_len = COMPAT_OFF_T_MAX;
> +	return 0;
> +}
> +

Erm...build break above though -- flock is a pointer there, so those
should be "flock->...". I'll just squash that fix into the patch unless
you need to send a respin for other reasons.

>  COMPAT_SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
>  		       compat_ulong_t, arg)
>  {
> -	mm_segment_t old_fs;
> -	struct flock f;
> -	long ret;
> -	unsigned int conv_cmd;
> +	struct fd f = fdget_raw(fd);
> +	struct flock flock;
> +	long err = -EBADF;
> +
> +	if (!f.file)
> +		return err;
> +
> +	if (unlikely(f.file->f_mode & FMODE_PATH)) {
> +		if (!check_fcntl_cmd(cmd))
> +			goto out_put;
> +	}
> +
> +	err = security_file_fcntl(f.file, cmd, arg);
> +	if (err)
> +		goto out_put;
>  
>  	switch (cmd) {
>  	case F_GETLK:
> +		err = get_compat_flock(&flock, compat_ptr(arg));
> +		if (err)
> +			break;
> +		err = fcntl_getlk(f.file, convert_fcntl_cmd(cmd), &flock);
> +		if (err)
> +			break;
> +		err = fixup_compat_flock(&flock);
> +		if (err)
> +			return err;
> +		err = put_compat_flock(&flock, compat_ptr(arg));
> +		break;
> +	case F_GETLK64:
> +	case F_OFD_GETLK:
> +		err = get_compat_flock64(&flock, compat_ptr(arg));
> +		if (err)
> +			break;
> +		err = fcntl_getlk(f.file, convert_fcntl_cmd(cmd), &flock);
> +		if (err)
> +			break;
> +		err = fixup_compat_flock(&flock);
> +		if (err)
> +			return err;
> +		err = put_compat_flock64(&flock, compat_ptr(arg));
> +		break;
>  	case F_SETLK:
>  	case F_SETLKW:
> -		ret = get_compat_flock(&f, compat_ptr(arg));
> -		if (ret != 0)
> +		err = get_compat_flock(&flock, compat_ptr(arg));
> +		if (err)
>  			break;
> -		old_fs = get_fs();
> -		set_fs(KERNEL_DS);
> -		ret = sys_fcntl(fd, cmd, (unsigned long)&f);
> -		set_fs(old_fs);
> -		if (cmd == F_GETLK && ret == 0) {
> -			/* 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
> -			 * -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
> -			 */
> -
> -			if (f.l_start > COMPAT_OFF_T_MAX)
> -				ret = -EOVERFLOW;
> -			if (f.l_len > COMPAT_OFF_T_MAX)
> -				f.l_len = COMPAT_OFF_T_MAX;
> -			if (ret == 0)
> -				ret = put_compat_flock(&f, compat_ptr(arg));
> -		}
> +		err = fcntl_setlk(fd, f.file, convert_fcntl_cmd(cmd), &flock);
>  		break;
> -
> -	case F_GETLK64:
>  	case F_SETLK64:
>  	case F_SETLKW64:
> -	case F_OFD_GETLK:
>  	case F_OFD_SETLK:
>  	case F_OFD_SETLKW:
> -		ret = get_compat_flock64(&f, compat_ptr(arg));
> -		if (ret != 0)
> +		err = get_compat_flock64(&flock, compat_ptr(arg));
> +		if (err)
>  			break;
> -		old_fs = get_fs();
> -		set_fs(KERNEL_DS);
> -		conv_cmd = convert_fcntl_cmd(cmd);
> -		ret = sys_fcntl(fd, conv_cmd, (unsigned long)&f);
> -		set_fs(old_fs);
> -		if ((conv_cmd == F_GETLK || conv_cmd == F_OFD_GETLK) && ret == 0) {
> -			/* need to return lock information - see above for commentary */
> -			if (f.l_start > COMPAT_LOFF_T_MAX)
> -				ret = -EOVERFLOW;
> -			if (f.l_len > COMPAT_LOFF_T_MAX)
> -				f.l_len = COMPAT_LOFF_T_MAX;
> -			if (ret == 0)
> -				ret = put_compat_flock64(&f, compat_ptr(arg));
> -		}
> +		err = fcntl_setlk(fd, f.file, convert_fcntl_cmd(cmd), &flock);
>  		break;
> -
>  	default:
> -		ret = sys_fcntl(fd, cmd, arg);
> +		err = do_fcntl(fd, cmd, arg, f.file);
>  		break;
>  	}
> -	return ret;
> +out_put:
> +	fdput(f);
> +	return err;
>  }
>  
>  COMPAT_SYSCALL_DEFINE3(fcntl, unsigned int, fd, unsigned int, cmd,
> diff --git a/fs/locks.c b/fs/locks.c
> index 054f6fb7641e..8b4e78e4c054 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -2325,7 +2325,7 @@ int fcntl_getlk64(struct file *filp, unsigned int cmd, struct flock64 *flock)
>  	if (error)
>  		goto out;
>  
> -	flock.l_type = file_lock.fl_type;
> +	flock->l_type = file_lock.fl_type;
>  	if (file_lock.fl_type != F_UNLCK)
>  		posix_lock_to_flock64(flock, &file_lock);
>  

-- 
Jeff Layton <jlayton@poochiereds.net>