From: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Tadeusz Struk <tadeusz.struk-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Cc: David Gibson
<david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>,
devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 1/2] libfdt: prevent integer overflow in fdt_next_tag
Date: Fri, 30 Sep 2022 08:18:30 -0500 [thread overview]
Message-ID: <CAL_JsqJ7E6D=jxmHXnh5cR_UyitpYVSPEQASsWu+eDyQ4J-Eig@mail.gmail.com> (raw)
In-Reply-To: <20220929235536.618370-1-tadeusz.struk-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
On Thu, Sep 29, 2022 at 6:55 PM Tadeusz Struk <tadeusz.struk-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> 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
comma: ...that, validate...
> read from the blob before doing calculations.
>
> Signed-off-by: Tadeusz Struk <tadeusz.struk-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
> libfdt/fdt.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/libfdt/fdt.c b/libfdt/fdt.c
> index 90a39e8..c3e112a 100644
> --- a/libfdt/fdt.c
> +++ b/libfdt/fdt.c
> @@ -186,11 +186,17 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset)
>
> case FDT_PROP:
> lenp = fdt_offset_ptr(fdt, offset, sizeof(*lenp));
> - if (!can_assume(VALID_DTB) && !lenp)
> + if (!can_assume(VALID_DTB) &&
> + (!lenp || (INT_MAX <= fdt32_to_cpu(*lenp))))
We now have fdt32_to_cpu(*lenp) 4 times. Stick it in a local var.
> return FDT_END; /* premature end */
> +
> /* skip-name offset, length and value */
> offset += sizeof(struct fdt_property) - FDT_TAGSIZE
> + fdt32_to_cpu(*lenp);
> +
> + if (offset < 0)
Needs a can_assume(VALID_DTB) check.
> + return FDT_END; /* premature end */
> +
> if (!can_assume(LATEST) &&
> fdt_version(fdt) < 0x10 && fdt32_to_cpu(*lenp) >= 8 &&
> ((offset - fdt32_to_cpu(*lenp)) % 8) != 0)
> --
> 2.37.3
>
prev parent reply other threads:[~2022-09-30 13:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-29 23:55 [PATCH 1/2] libfdt: prevent integer overflow in fdt_next_tag Tadeusz Struk
[not found] ` <20220929235536.618370-1-tadeusz.struk-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
2022-09-29 23:55 ` [PATCH 2/2] libfdt: tests: add get_next_tag_invalid_prop_len Tadeusz Struk
2022-09-30 13:18 ` Rob Herring [this message]
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