Messages in this thread Patch in this message | | | Date | Wed, 7 Mar 2018 15:40:19 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] vsprintf: Remove accidental VLA usage |
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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?
--- 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)]; _
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