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Message-ID: <20180307234238.yxbbaka35ck2xymw@smitten> Date: Wed, 7 Mar 2018 16:42:38 -0700 From: Tycho Andersen <tycho@...ho.ws> To: Kees Cook <keescook@...omium.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, "Tobin C. Harding" <me@...in.cc>, Jonathan Corbet <corbet@....net>, Pantelis Antoniou <pantelis.antoniou@...sulko.com>, "Steven Rostedt (VMware)" <rostedt@...dmis.org>, kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org, "Gustavo A. R. Silva" <gustavo@...eddedor.com> Subject: Re: [PATCH] vsprintf: Remove accidental VLA usage Hi Kees, On Wed, Mar 07, 2018 at 03:07:14PM -0800, Kees Cook wrote: > The "sym" calculation is actually a fixed size, but since the max() > macro uses some extensive tricks for safety, it ends up looking like a > variable size. This replaces max() with a simple max macro which is > sufficient for the calculation of the array size. > > Seen with -Wvla. Fixed as part of the directive to remove all VLAs from > the kernel: https://lkml.org/lkml/2018/3/7/621 > > Signed-off-by: Kees Cook <keescook@...omium.org> > --- > lib/vsprintf.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index d7a708f82559..f420ab1477cb 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -744,8 +744,9 @@ char *resource_string(char *buf, char *end, struct resource *res, > #define FLAG_BUF_SIZE (2 * sizeof(res->flags)) > #define DECODED_BUF_SIZE sizeof("[mem - 64bit pref window disabled]") > #define RAW_BUF_SIZE sizeof("[mem - flags 0x]") > - char sym[max(2*RSRC_BUF_SIZE + DECODED_BUF_SIZE, > - 2*RSRC_BUF_SIZE + FLAG_BUF_SIZE + RAW_BUF_SIZE)]; > +#define SIMPLE_MAX(x, y) ((x) > (y) ? (x) : (y)) It's probably worth hoisting this out into some other header. When I was looking at this a while ago, this problem happens in a few places, see e.g. net/ipv4/proc.c:TCPUDP_MIB_MAX. Cheers, Tycho
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