Re: [PATCH 05/30] xfs: use strndup_user in XFS_IOC_ATTRMULTI_BY_HANDLE

From: Chandan Rajendra <chandan@linux.ibm.com>
To: Christoph Hellwig <hch@lst.de>
Cc: linux-xfs@vger.kernel.org,
	Allison Collins <allison.henderson@oracle.com>,
	"Darrick J . Wong" <darrick.wong@oracle.com>
Subject: Re: [PATCH 05/30] xfs: use strndup_user in XFS_IOC_ATTRMULTI_BY_HANDLE
Date: Thu, 06 Feb 2020 16:03:55 +0530	[thread overview]
Message-ID: <3011142.zga9gAiKYx@localhost.localdomain> (raw)
In-Reply-To: <20200129170310.51370-6-hch@lst.de>

On Wednesday, January 29, 2020 10:32 PM Christoph Hellwig wrote: 

> Simplify the user copy code by using strndup_user.  This means that we
> now do one memory allocation per operation instead of one per ioctl,
> but memory allocations are cheap compared to the actual file system
> operations.
>

The newly introduced changes logically match with the code flow that existed
earlier.

Reviewed-by: Chandan Rajendra <chandanrlinux@gmail.com>

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/xfs_ioctl.c   | 17 +++++------------
>  fs/xfs/xfs_ioctl32.c | 17 +++++------------
>  2 files changed, 10 insertions(+), 24 deletions(-)
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index b806003caacd..bb490a954c0b 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -448,11 +448,6 @@ xfs_attrmulti_by_handle(
>  		goto out_dput;
>  	}
> 
> -	error = -ENOMEM;
> -	attr_name = kmalloc(MAXNAMELEN, GFP_KERNEL);
> -	if (!attr_name)
> -		goto out_kfree_ops;
> -
>  	error = 0;
>  	for (i = 0; i < am_hreq.opcount; i++) {
>  		if ((ops[i].am_flags & ATTR_ROOT) &&
> @@ -462,12 +457,11 @@ xfs_attrmulti_by_handle(
>  		}
>  		ops[i].am_flags &= ~ATTR_KERNEL_FLAGS;
> 
> -		ops[i].am_error = strncpy_from_user((char *)attr_name,
> -				ops[i].am_attrname, MAXNAMELEN);
> -		if (ops[i].am_error == 0 || ops[i].am_error == MAXNAMELEN)
> -			error = -ERANGE;
> -		if (ops[i].am_error < 0)
> +		attr_name = strndup_user(ops[i].am_attrname, MAXNAMELEN);
> +		if (IS_ERR(attr_name)) {
> +			ops[i].am_error = PTR_ERR(attr_name);
>  			break;
> +		}
> 
>  		switch (ops[i].am_opcode) {
>  		case ATTR_OP_GET:
> @@ -498,13 +492,12 @@ xfs_attrmulti_by_handle(
>  		default:
>  			ops[i].am_error = -EINVAL;
>  		}
> +		kfree(attr_name);
>  	}
> 
>  	if (copy_to_user(am_hreq.ops, ops, size))
>  		error = -EFAULT;
> 
> -	kfree(attr_name);
> - out_kfree_ops:
>  	kfree(ops);
>   out_dput:
>  	dput(dentry);
> diff --git a/fs/xfs/xfs_ioctl32.c b/fs/xfs/xfs_ioctl32.c
> index e085f304e539..936c2f62fb6c 100644
> --- a/fs/xfs/xfs_ioctl32.c
> +++ b/fs/xfs/xfs_ioctl32.c
> @@ -445,11 +445,6 @@ xfs_compat_attrmulti_by_handle(
>  		goto out_dput;
>  	}
> 
> -	error = -ENOMEM;
> -	attr_name = kmalloc(MAXNAMELEN, GFP_KERNEL);
> -	if (!attr_name)
> -		goto out_kfree_ops;
> -
>  	error = 0;
>  	for (i = 0; i < am_hreq.opcount; i++) {
>  		if ((ops[i].am_flags & ATTR_ROOT) &&
> @@ -459,13 +454,12 @@ xfs_compat_attrmulti_by_handle(
>  		}
>  		ops[i].am_flags &= ~ATTR_KERNEL_FLAGS;
> 
> -		ops[i].am_error = strncpy_from_user((char *)attr_name,
> -				compat_ptr(ops[i].am_attrname),
> +		attr_name = strndup_user(compat_ptr(ops[i].am_attrname),
>  				MAXNAMELEN);
> -		if (ops[i].am_error == 0 || ops[i].am_error == MAXNAMELEN)
> -			error = -ERANGE;
> -		if (ops[i].am_error < 0)
> +		if (IS_ERR(attr_name)) {
> +			ops[i].am_error = PTR_ERR(attr_name);
>  			break;
> +		}
> 
>  		switch (ops[i].am_opcode) {
>  		case ATTR_OP_GET:
> @@ -496,13 +490,12 @@ xfs_compat_attrmulti_by_handle(
>  		default:
>  			ops[i].am_error = -EINVAL;
>  		}
> +		kfree(attr_name);
>  	}
> 
>  	if (copy_to_user(compat_ptr(am_hreq.ops), ops, size))
>  		error = -EFAULT;
> 
> -	kfree(attr_name);
> - out_kfree_ops:
>  	kfree(ops);
>   out_dput:
>  	dput(dentry);
> 

-- 
chandan