altera-stapl: altera_get_note: prevent write beyond end of 'key'

altera-stapl: altera_get_note: prevent write beyond end of 'key'

altera_get_note is called from altera_init, where key is kzalloc(33).

When the allocation functions are annotated to allow the compiler to see
the sizes of objects, and with FORTIFY_SOURCE, we see:

In file included from drivers/misc/altera-stapl/altera.c:14:0:
In function ‘strlcpy’,
    inlined from ‘altera_init’ at drivers/misc/altera-stapl/altera.c:2189:5:
include/linux/string.h:378:4: error: call to ‘__write_overflow’ declared with attribute error: detected write beyond size of object passed as 1st parameter
    __write_overflow();
    ^~~~~~~~~~~~~~~~~~

That refers to this code in altera_get_note:

    if (key != NULL)
            strlcpy(key, &p[note_strings +
                            get_unaligned_be32(
                            &p[note_table + (8 * i)])],
                    length);

The error triggers because the length of 'key' is 33, but the copy
uses length supplied as the 'length' parameter, which is always
256. Split the size parameter into key_len and val_len, and use the
appropriate length depending on what is being copied.

Detected by compiler error, only compile-tested.

Cc: "Igor M. Liplianin" <liplianin@netup.ru>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Link: https://lore.kernel.org/r/20200120074344.504-2-dja@axtens.net
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/202002251042.D898E67AC@keescook
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>