linux-kernel - Re: [lustre-devel] [PATCH v2] staging: lustre: Remove VLA usage

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Message-ID: <D86B331F-466E-4395-9620-A84349F2DD2E@intel.com>
Date:   Fri, 9 Mar 2018 08:54:29 +0000
From:   "Dilger, Andreas" <andreas.dilger@...el.com>
To:     Kees Cook <keescook@...omium.org>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        Tycho Andersen <tycho@...ho.ws>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Gargi Sharma <gs051095@...il.com>,
        "Drokin, Oleg" <oleg.drokin@...el.com>,
        Lustre Development List <lustre-devel@...ts.lustre.org>,
        "Tobin C. Harding" <me@...in.cc>
Subject: Re: [lustre-devel] [PATCH v2] staging: lustre: Remove VLA usage

On Mar 7, 2018, at 13:54, Kees Cook <keescook@...omium.org> wrote:
> 
> The kernel would like to have all stack VLA usage removed[1]. This switches
> to a simple kasprintf() instead, and in the process fixes an off-by-one
> between the allocation and the sprintf (allocation did not include NULL
> byte in calculation).
> 
> [1] https://lkml.org/lkml/2018/3/7/621
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> Reviewed-by: Rasmus Villemoes <linux@...musvillemoes.dk>

This seems better than the VLA_SAFE() macro, at the cost of an extra kmalloc.
I don't think these code paths are super performance critical.

Reviewed-by: Andreas Dilger <andreas.dilger@...el.com>

> ---
> drivers/staging/lustre/lustre/llite/xattr.c | 19 +++++++++++++------
> 1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/staging/lustre/lustre/llite/xattr.c b/drivers/staging/lustre/lustre/llite/xattr.c
> index 532384c91447..ff6fe81a4ddb 100644
> --- a/drivers/staging/lustre/lustre/llite/xattr.c
> +++ b/drivers/staging/lustre/lustre/llite/xattr.c
> @@ -87,10 +87,10 @@ ll_xattr_set_common(const struct xattr_handler *handler,
> 		    const char *name, const void *value, size_t size,
> 		    int flags)
> {
> -	char fullname[strlen(handler->prefix) + strlen(name) + 1];
> 	struct ll_sb_info *sbi = ll_i2sbi(inode);
> 	struct ptlrpc_request *req = NULL;
> 	const char *pv = value;
> +	char *fullname;
> 	__u64 valid;
> 	int rc;
> 
> @@ -141,10 +141,13 @@ ll_xattr_set_common(const struct xattr_handler *handler,
> 			return -EPERM;
> 	}
> 
> -	sprintf(fullname, "%s%s\n", handler->prefix, name);
> +	fullname = kasprintf(GFP_KERNEL, "%s%s\n", handler->prefix, name);
> +	if (!fullname)
> +		return -ENOMEM;
> 	rc = md_setxattr(sbi->ll_md_exp, ll_inode2fid(inode),
> 			 valid, fullname, pv, size, 0, flags,
> 			 ll_i2suppgid(inode), &req);
> +	kfree(fullname);
> 	if (rc) {
> 		if (rc == -EOPNOTSUPP && handler->flags == XATTR_USER_T) {
> 			LCONSOLE_INFO("Disabling user_xattr feature because it is not supported on the server\n");
> @@ -364,11 +367,11 @@ static int ll_xattr_get_common(const struct xattr_handler *handler,
> 			       struct dentry *dentry, struct inode *inode,
> 			       const char *name, void *buffer, size_t size)
> {
> -	char fullname[strlen(handler->prefix) + strlen(name) + 1];
> 	struct ll_sb_info *sbi = ll_i2sbi(inode);
> #ifdef CONFIG_FS_POSIX_ACL
> 	struct ll_inode_info *lli = ll_i2info(inode);
> #endif
> +	char *fullname;
> 	int rc;
> 
> 	CDEBUG(D_VFSTRACE, "VFS Op:inode=" DFID "(%p)\n",
> @@ -411,9 +414,13 @@ static int ll_xattr_get_common(const struct xattr_handler *handler,
> 	if (handler->flags == XATTR_ACL_DEFAULT_T && !S_ISDIR(inode->i_mode))
> 		return -ENODATA;
> #endif
> -	sprintf(fullname, "%s%s\n", handler->prefix, name);
> -	return ll_xattr_list(inode, fullname, handler->flags, buffer, size,
> -			     OBD_MD_FLXATTR);
> +	fullname = kasprintf(GFP_KERNEL, "%s%s\n", handler->prefix, name);
> +	if (!fullname)
> +		return -ENOMEM;
> +	rc = ll_xattr_list(inode, fullname, handler->flags, buffer, size,
> +			   OBD_MD_FLXATTR);
> +	kfree(fullname);
> +	return rc;
> }
> 
> static ssize_t ll_getxattr_lov(struct inode *inode, void *buf, size_t buf_size)
> -- 
> 2.7.4
> 
> 
> -- 
> Kees Cook
> Pixel Security
> _______________________________________________
> lustre-devel mailing list
> lustre-devel@...ts.lustre.org
> http://lists.lustre.org/listinfo.cgi/lustre-devel-lustre.org

Cheers, Andreas
--
Andreas Dilger
Lustre Principal Architect
Intel Corporation