From: David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>
To: Jan Beulich <jbeulich-IBi9RG/b67k@public.gmane.org>
Cc: Jon Loeliger <jdl-CYoMK+44s/E@public.gmane.org>,
devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH] libfdt: fix undefined behaviour in fdt_splice_()
Date: Wed, 11 Mar 2020 15:59:14 +1100 [thread overview]
Message-ID: <20200311045914.GY660117@umbus.fritz.box> (raw)
In-Reply-To: <f2d09e81-7cb8-c5cc-9699-1ac05b0626ff-IBi9RG/b67k@public.gmane.org>
[-- Attachment #1: Type: text/plain, Size: 2426 bytes --]
On Thu, Mar 05, 2020 at 03:04:45PM +0100, Jan Beulich wrote:
> libfdt: fix undefined behaviour in fdt_splice_()
>
> Along the lines of commit d0b3ab0a0f46 ("libfdt: Fix undefined behaviour
> in fdt_offset_ptr()"), fdt_splice_() similarly may not use pointer
> arithmetic to do overflow checks. (The left side of the checks added by
> d4c7c25c9ed1 ["libfdt: check for potential overrun in _fdt_splice()"]
> doesn't really lend itself to similar replacement though.)
>
> Signed-off-by: Jan Beulich <jbeulich-IBi9RG/b67k@public.gmane.org>
Applied, thanks.
> ---
> The right side of the checks added by d4c7c25c9ed1 looks suspicious,
> which is more noticable after the transformation done here:
>
> end - oldlen + newlen < (char *)fdt
>
> end - (char *)fdt + newlen < oldlen
>
> dsize + newlen < oldlen
Hrm, yeah, I think this is trying to check for overflow of
dsize+newlen, but it's pretty hard to follow.
>
> --- a/libfdt/fdt_rw.c
> +++ b/libfdt/fdt_rw.c
> @@ -46,7 +46,7 @@ static int fdt_rw_probe_(void *fdt)
> return err_; \
> }
>
> -static inline int fdt_data_size_(void *fdt)
> +static inline unsigned int fdt_data_size_(void *fdt)
> {
> return fdt_off_dt_strings(fdt) + fdt_size_dt_strings(fdt);
> }
> @@ -54,15 +54,16 @@ static inline int fdt_data_size_(void *f
> static int fdt_splice_(void *fdt, void *splicepoint, int oldlen, int newlen)
> {
> char *p = splicepoint;
> - char *end = (char *)fdt + fdt_data_size_(fdt);
> + unsigned int dsize = fdt_data_size_(fdt);
> + size_t soff = p - (char *)fdt;
>
> - if (((p + oldlen) < p) || ((p + oldlen) > end))
> + if ((oldlen < 0) || (soff + oldlen < soff) || (soff + oldlen > dsize))
> return -FDT_ERR_BADOFFSET;
> - if ((p < (char *)fdt) || ((end - oldlen + newlen) < (char *)fdt))
> + if ((p < (char *)fdt) || (dsize + newlen < oldlen))
> return -FDT_ERR_BADOFFSET;
> - if ((end - oldlen + newlen) > ((char *)fdt + fdt_totalsize(fdt)))
> + if (dsize - oldlen + newlen > fdt_totalsize(fdt))
> return -FDT_ERR_NOSPACE;
> - memmove(p + newlen, p + oldlen, end - p - oldlen);
> + memmove(p + newlen, p + oldlen, ((char *)fdt + dsize) - (p + oldlen));
> return 0;
> }
>
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
next prev parent reply other threads:[~2020-03-11 4:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-05 14:04 [PATCH] libfdt: fix undefined behaviour in fdt_splice_() Jan Beulich
[not found] ` <f2d09e81-7cb8-c5cc-9699-1ac05b0626ff-IBi9RG/b67k@public.gmane.org>
2020-03-11 4:59 ` David Gibson [this message]
[not found] ` <20200311045914.GY660117-K0bRW+63XPQe6aEkudXLsA@public.gmane.org>
2020-03-12 8:19 ` Jan Beulich
[not found] ` <4eaa4349-edbf-eb53-637d-b62a20befddd-IBi9RG/b67k@public.gmane.org>
2020-03-13 0:24 ` David Gibson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200311045914.GY660117@umbus.fritz.box \
--to=david-xt8fgy+axnrb3ne2bgzf6laj5h9x9tb+@public.gmane.org \
--cc=devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
--cc=jbeulich-IBi9RG/b67k@public.gmane.org \
--cc=jdl-CYoMK+44s/E@public.gmane.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).