| Message ID | 20180307154019.e39890b5f8aa98cf25532cf1@linux-foundation.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Mar 7, 2018 at 3:40 PM, Andrew Morton <akpm@linux-foundation.org> wrote: > On Wed, 7 Mar 2018 15:07:14 -0800 Kees Cook <keescook@chromium.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? Hopefully a year from now we'll have added -Wvla to the global build flags and no one will be able to try that. :) -Kees
--- 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)];