linux-hardening - Re: [PATCH] xfs: cleanup deprecated uses of strncpy

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Message-ID: <20240403041100.GQ6390@frogsfrogsfrogs>
Date: Tue, 2 Apr 2024 21:11:00 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Chandan Babu R <chandan.babu@...cle.com>, linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] xfs: cleanup deprecated uses of strncpy

On Mon, Apr 01, 2024 at 11:01:38PM +0000, Justin Stitt wrote:
> strncpy() is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> In xfs_ioctl.c:
> The current code has taken care NUL-termination by memset()'ing @label.
> This is followed by a strncpy() to perform the string copy.
> 
> Use strscpy_pad() to get both 1) NUL-termination and 2) NUL-padding
> which may be needed as this is copied out to userspace.
> 
> Note that this patch uses the new 2-argument version of strscpy_pad
> introduced in Commit e6584c3964f2f ("string: Allow 2-argument
> strscpy()").
> 
> In xfs_xattr.c:
> There's a lot of manual memory management to get a prefix and name into
> a string. Let's use an easier to understand and more robust interface in
> scnprintf() to accomplish the same task.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Note: build-tested only.

fstested would be better. ;)

Anyway I guess that looks ok so let's find out:
Reviewed-by: Darrick J. Wong <djwong@...nel.org>

--D

> 
> Found with: $ rg "strncpy\("
> ---
>  fs/xfs/xfs_ioctl.c | 4 +---
>  fs/xfs/xfs_xattr.c | 6 +-----
>  2 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index d0e2cec6210d..abef9707a433 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1755,10 +1755,8 @@ xfs_ioc_getlabel(
>  	/* Paranoia */
>  	BUILD_BUG_ON(sizeof(sbp->sb_fname) > FSLABEL_MAX);
>  
> -	/* 1 larger than sb_fname, so this ensures a trailing NUL char */
> -	memset(label, 0, sizeof(label));
>  	spin_lock(&mp->m_sb_lock);
> -	strncpy(label, sbp->sb_fname, XFSLABEL_MAX);
> +	strscpy_pad(label, sbp->sb_fname);
>  	spin_unlock(&mp->m_sb_lock);
>  
>  	if (copy_to_user(user_label, label, sizeof(label)))
> diff --git a/fs/xfs/xfs_xattr.c b/fs/xfs/xfs_xattr.c
> index 364104e1b38a..b9256988830f 100644
> --- a/fs/xfs/xfs_xattr.c
> +++ b/fs/xfs/xfs_xattr.c
> @@ -220,11 +220,7 @@ __xfs_xattr_put_listent(
>  		return;
>  	}
>  	offset = context->buffer + context->count;
> -	memcpy(offset, prefix, prefix_len);
> -	offset += prefix_len;
> -	strncpy(offset, (char *)name, namelen);			/* real name */
> -	offset += namelen;
> -	*offset = '\0';
> +	scnprintf(offset, prefix_len + namelen + 1, "%s%s", prefix, name);
>  
>  compute_size:
>  	context->count += prefix_len + namelen + 1;
> 
> ---
> base-commit: 928a87efa42302a23bb9554be081a28058495f22
> change-id: 20240401-strncpy-fs-xfs-xfs_ioctl-c-8af7a895bff0
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 
>