From: Kees Cook <keescook@chromium•org>
To: Nathan Lynch <nathanl@linux•ibm.com>
Cc: Leonardo Bras <leobras.c@gmail•com>,
linuxppc-dev@lists•ozlabs.org,
Andrew Donnellan <ajd@linux•ibm.com>,
linux-hardening@vger•kernel.org
Subject: Re: [PATCH] powerpc/rtas: Replace one-element arrays with flexible arrays
Date: Fri, 27 Jan 2023 11:23:57 -0800 [thread overview]
Message-ID: <202301271120.B83DA0B3@keescook> (raw)
In-Reply-To: <87357wp1h7.fsf@linux.ibm.com>
On Fri, Jan 27, 2023 at 07:10:28AM -0600, Nathan Lynch wrote:
> Andrew Donnellan <ajd@linux•ibm.com> writes:
> > Using a one-element array as a fake flexible array is deprecated.
> >
> > Replace the one-element flexible arrays in rtas-types.h with C99 standard
> > flexible array members instead.
> >
> > This helps us move towards enabling -fstrict-flex-arrays=3 in future.
> >
> > Found using scripts/coccinelle/misc/flexible_array.cocci.
> >
> > Cc: Nathan Lynch <nathanl@linux•ibm.com>
> > Cc: Leonardo Bras <leobras.c@gmail•com>
> > Cc: linux-hardening@vger•kernel.org
> > Link: https://github.com/KSPP/linux/issues/21
> > Link: https://github.com/KSPP/linux/issues/79
> > Signed-off-by: Andrew Donnellan <ajd@linux•ibm.com>
> > ---
> > arch/powerpc/include/asm/rtas-types.h | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/rtas-types.h b/arch/powerpc/include/asm/rtas-types.h
> > index 8df6235d64d1..40ec03a05c0b 100644
> > --- a/arch/powerpc/include/asm/rtas-types.h
> > +++ b/arch/powerpc/include/asm/rtas-types.h
> > @@ -44,7 +44,7 @@ struct rtas_error_log {
> > */
> > u8 byte3; /* General event or error*/
> > __be32 extended_log_length; /* length in bytes */
> > - unsigned char buffer[1]; /* Start of extended log */
> > + unsigned char buffer[]; /* Start of extended log */
> > /* Variable length. */
> > };
> >
> > @@ -85,7 +85,7 @@ struct rtas_ext_event_log_v6 {
> > /* that defines the format for */
> > /* the vendor specific log type */
> > /* Byte 16-end of log */
> > - u8 vendor_log[1]; /* Start of vendor specific log */
> > + u8 vendor_log[]; /* Start of vendor specific log */
> > /* Variable length. */
> > };
>
> I see at least one place that consults the size of one of these structs,
> in get_pseries_errorlog():
>
> /* Check that we understand the format */
> if (ext_log_length < sizeof(struct rtas_ext_event_log_v6) || ...
>
> Don't all such sites need to be audited/adjusted for changes like this?
Yeah, I'd expect a binary comparison[1] before/after to catch things like
this. E.g. the following C files mention those structs:
arch/powerpc/platforms/pseries/io_event_irq.c
arch/powerpc/platforms/pseries/ras.c
arch/powerpc/kernel/rtasd.c
arch/powerpc/kernel/rtas.c
-Kees
[1] https://outflux.net/blog/archives/2022/06/24/finding-binary-differences/
--
Kees Cook
next prev parent reply other threads:[~2023-01-27 19:25 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-27 8:50 [PATCH] powerpc/rtas: Replace one-element arrays with flexible arrays Andrew Donnellan
2023-01-27 8:59 ` Leonardo Brás
2023-01-27 13:10 ` Nathan Lynch
2023-01-27 19:23 ` Kees Cook [this message]
2023-04-20 7:46 ` Andrew Donnellan
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