From: David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>
To: Tadeusz Struk <tadeusz.struk-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Cc: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH v3 1/2] libfdt: prevent integer overflow in fdt_next_tag
Date: Wed, 12 Oct 2022 10:51:08 +1100 [thread overview]
Message-ID: <Y0YBbEEZGtMh+o7U@yekko> (raw)
In-Reply-To: <20221005232931.3016047-1-tadeusz.struk-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
[-- Attachment #1: Type: text/plain, Size: 2386 bytes --]
On Wed, Oct 05, 2022 at 04:29:30PM -0700, Tadeusz Struk wrote:
> Since fdt_next_tag() in a public API function all input parameters,
> including the fdt blob should not be trusted. It is possible to forge
> a blob with invalid property length that will cause integer overflow
> during offset calculation. To prevent that, validate the property length
> read from the blob before doing calculations.
>
> Signed-off-by: Tadeusz Struk <tadeusz.struk-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Merged, thanks.
> ---
> v2:
> * Use len local variable to avoid multiple calls to fdt32_to_cpu(*lenp)
> * Add can_assume(VALID_DTB) to the new checks
> v3:
> * Use unsigned integer for prop len and offset validation
> ---
> libfdt/fdt.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/libfdt/fdt.c b/libfdt/fdt.c
> index 90a39e8..20c6415 100644
> --- a/libfdt/fdt.c
> +++ b/libfdt/fdt.c
> @@ -162,7 +162,7 @@ const void *fdt_offset_ptr(const void *fdt, int offset, unsigned int len)
> uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset)
> {
> const fdt32_t *tagp, *lenp;
> - uint32_t tag;
> + uint32_t tag, len, sum;
> int offset = startoffset;
> const char *p;
>
> @@ -188,12 +188,19 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset)
> lenp = fdt_offset_ptr(fdt, offset, sizeof(*lenp));
> if (!can_assume(VALID_DTB) && !lenp)
> return FDT_END; /* premature end */
> +
> + len = fdt32_to_cpu(*lenp);
> + sum = len + offset;
> + if (!can_assume(VALID_DTB) &&
> + (INT_MAX <= sum || sum < (uint32_t) offset))
> + return FDT_END; /* premature end */
> +
> /* skip-name offset, length and value */
> - offset += sizeof(struct fdt_property) - FDT_TAGSIZE
> - + fdt32_to_cpu(*lenp);
> + offset += sizeof(struct fdt_property) - FDT_TAGSIZE + len;
> +
> if (!can_assume(LATEST) &&
> - fdt_version(fdt) < 0x10 && fdt32_to_cpu(*lenp) >= 8 &&
> - ((offset - fdt32_to_cpu(*lenp)) % 8) != 0)
> + fdt_version(fdt) < 0x10 && len >= 8 &&
> + ((offset - len) % 8) != 0)
> offset += 4;
> break;
>
--
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 --]
prev parent reply other threads:[~2022-10-11 23:51 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-05 23:29 [PATCH v3 1/2] libfdt: prevent integer overflow in fdt_next_tag Tadeusz Struk
[not found] ` <20221005232931.3016047-1-tadeusz.struk-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
2022-10-05 23:29 ` [PATCH v3 2/2] libfdt: tests: add get_next_tag_invalid_prop_len Tadeusz Struk
[not found] ` <20221005232931.3016047-2-tadeusz.struk-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
2022-10-06 8:06 ` David Gibson
2022-10-06 16:36 ` Tadeusz Struk
2022-10-06 7:52 ` [PATCH v3 1/2] libfdt: prevent integer overflow in fdt_next_tag David Gibson
2022-10-11 23:51 ` David Gibson [this message]
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=Y0YBbEEZGtMh+o7U@yekko \
--to=david-xt8fgy+axnrb3ne2bgzf6laj5h9x9tb+@public.gmane.org \
--cc=devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
--cc=devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
--cc=robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org \
--cc=tadeusz.struk-QSEj5FYQhm4dnm+yROfE0A@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).