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    SubjectRe: [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@chromium.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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