linux-kernel - Re: [PATCH] staging: lustre: llite: replace variable length array

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Message-ID: <alpine.LFD.2.21.1802112136420.21780@casper.infradead.org>
Date:   Sun, 11 Feb 2018 21:38:01 +0000 (GMT)
From:   James Simmons <jsimmons@...radead.org>
To:     Sven Dziadek <sven.dziadek@....de>
cc:     "Dilger, Andreas" <andreas.dilger@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Drokin, Oleg" <oleg.drokin@...el.com>,
        lkml <linux-kernel@...r.kernel.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        lustre-devel <lustre-devel@...ts.lustre.org>,
        "Eremin, Dmitry" <dmitry.eremin@...el.com>
Subject: Re: [PATCH] staging: lustre: llite: replace variable length array


> On 01/30/2018 03:04 AM, Dilger, Andreas wrote:
> > On Jan 27, 2018, at 14:42, Sven Dziadek <sven.dziadek@....de> wrote:
> >>
> >> The functionality of the removed variable length array is already
> >> implemented by the function xattr_full_name in fs/xattr.c
> >>
> >> This fixes the sparse warning:
> >> warning: Variable length array is used.
> >>
> >> Signed-off-by: Sven Dziadek <sven.dziadek@....de>
> >> ---
> >> drivers/staging/lustre/lustre/llite/xattr.c | 12 ++++--------
> >> 1 file changed, 4 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/drivers/staging/lustre/lustre/llite/xattr.c b/drivers/staging/lustre/lustre/llite/xattr.c
> >> index 532384c91447..4fd28213c6a1 100644
> >> --- a/drivers/staging/lustre/lustre/llite/xattr.c
> >> +++ b/drivers/staging/lustre/lustre/llite/xattr.c
> >> @@ -87,7 +87,6 @@ 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;
> >> @@ -141,9 +140,8 @@ ll_xattr_set_common(const struct xattr_handler *handler,
> >> 			return -EPERM;
> >> 	}
> >>
> >> -	sprintf(fullname, "%s%s\n", handler->prefix, name);
> >> -	rc = md_setxattr(sbi->ll_md_exp, ll_inode2fid(inode),
> >> -			 valid, fullname, pv, size, 0, flags,
> >> +	rc = md_setxattr(sbi->ll_md_exp, ll_inode2fid(inode), valid,
> >> +			 xattr_full_name(handler, name), pv, size, 0, flags,
> >> 			 ll_i2suppgid(inode), &req);
> > 
> > Hi Sven,
> > thanks for the patch.
> > 
> > Looking at the details of "xattr_full_name()", this seems quite risky.  This
> > is essentially returning the pointer _before_ "name" on the assumption that
> > it contains the full "prefix.name" string.  IMHO, that is not necessarily a
> > safe assumption to make several layers down in the code.
> Thanks for your reply. And yeah, it feels strange, right.
> 
> But it really looks like this is how the name and the prefix is handled
> in the xattr code.
> It seems this helper function has been introduced with commit
> e409de992e3ea (which also removes some fullname pointer) and indeed,
> fs/xattr.c splits the prefix and the name in xattr_resolve_name.
> 
> So I still think the patch should be correct..?
> 
> > James, I thought you had a patch for this to use kasprintf() instead of the
> > on-stack "fullname" declaration?
> Sorry for replying that late, I though James would maybe know if the
> above assumption is correct..

Yes I do have a patch for this. I pushed them several months ago but they
got missed. It happens. I will the patches again very soon.
 
> >> 	if (rc) {
> >> 		if (rc == -EOPNOTSUPP && handler->flags == XATTR_USER_T) {
> >> @@ -364,7 +362,6 @@ 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);
> >> @@ -411,9 +408,8 @@ 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);
> >> +	return ll_xattr_list(inode, xattr_full_name(handler, name),
> >> +			     handler->flags, buffer, size, OBD_MD_FLXATTR);
> >> }
> >>
> >> static ssize_t ll_getxattr_lov(struct inode *inode, void *buf, size_t buf_size)
> >> -- 
> >> 2.11.0
> >>
> 
>