|
Message-Id: <20180307154019.e39890b5f8aa98cf25532cf1@linux-foundation.org> Date: Wed, 7 Mar 2018 15:40:19 -0800 From: Andrew Morton <akpm@...ux-foundation.org> To: Kees Cook <keescook@...omium.org> Cc: "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 On Wed, 7 Mar 2018 15:07:14 -0800 Kees Cook <keescook@...omium.org> 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 > > ... > > --- 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)) > + char sym[SIMPLE_MAX(2*RSRC_BUF_SIZE + DECODED_BUF_SIZE, > + 2*RSRC_BUF_SIZE + FLAG_BUF_SIZE + RAW_BUF_SIZE)]; > > char *p = sym, *pend = sym + sizeof(sym); > int decode = (fmt[0] == 'R') ? 1 : 0; A year from now I'll be receiving an email titled [patch] lib/vsprintf.c: use standard max() macro won't I? --- a/lib/vsprintf.c~vsprintf-remove-accidental-vla-usage-fix +++ a/lib/vsprintf.c @@ -754,6 +754,7 @@ char *resource_string(char *buf, char *e #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]") +/* regular max() tricks gcc into creating a variable length array */ #define SIMPLE_MAX(x, y) ((x) > (y) ? (x) : (y)) char sym[SIMPLE_MAX(2*RSRC_BUF_SIZE + DECODED_BUF_SIZE, 2*RSRC_BUF_SIZE + FLAG_BUF_SIZE + RAW_BUF_SIZE)]; _
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.