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Date: Thu, 8 Mar 2018 13:43:09 +0300
From: Dan Carpenter <dan.carpenter@...cle.com>
To: Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc: Kees Cook <keescook@...omium.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
devel@...verdev.osuosl.org, Dmitry Eremin <dmitry.eremin@...el.com>,
Tycho Andersen <tycho@...ho.ws>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
linux-kernel@...r.kernel.org, Gargi Sharma <gs051095@...il.com>,
Oleg Drokin <oleg.drokin@...el.com>,
Andreas Dilger <andreas.dilger@...el.com>,
lustre-devel@...ts.lustre.org
Subject: Re: [PATCH] staging: lustre: Remove VLA usage
On Wed, Mar 07, 2018 at 02:10:41PM +0100, Rasmus Villemoes wrote:
> On 2018-03-07 06:46, Kees Cook wrote:
> > The kernel would like to remove all VLA usage. This switches to a
> > simple kasprintf() instead.
> >
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> > 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..aab4eab64289 100644
> > --- a/drivers/staging/lustre/lustre/llite/xattr.c
> > +++ b/drivers/staging/lustre/lustre/llite/xattr.c
> > @@ -87,7 +87,7 @@ 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];
> > + char *fullname;
> > struct ll_sb_info *sbi = ll_i2sbi(inode);
> > struct ptlrpc_request *req = NULL;
> > const char *pv = value;
> > @@ -141,10 +141,13 @@ ll_xattr_set_common(const struct xattr_handler *handler,
> > return -EPERM;
> > }
> >
> > - sprintf(fullname, "%s%s\n", handler->prefix, name);
>
> It's probably worth pointing out that this actually fixes an
> unconditional buffer overflow: fullname only has room for the two
> strings and the '\n', but vsnprintf() is told that the buffer has
> infinite size (well, INT_MAX), so there should be plenty of room to
> append the '\0' after the '\n'.
>
> > + 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");
> > @@ -364,7 +367,7 @@ 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];
> > + char *fullname;
> > struct ll_sb_info *sbi = ll_i2sbi(inode);
> > #ifdef CONFIG_FS_POSIX_ACL
> > struct ll_inode_info *lli = ll_i2info(inode);
> > @@ -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);
>
> Same here.
>
> I'm a little surprised this hasn't been caugt by static analysis, I
> thought gcc/coverity/smatch/whatnot had gotten pretty good at computing
> the size of the output generated by a given format string with "known"
> arguments and comparing to the size of the output buffer. Though of
> course it does require the tool to be able to do symbolic manipulations,
> in this case realizing that
>
> outsize == strlen(x)+strlen(y)+1+1 > bufsize == strlen(x)+strlen(y)+1
That kind of symbolic manipulation is crazy hard to do.
regards,
dan carpenter
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