binfmt_flat: Fix integer overflow bug on 32 bit systems

commit 55cf2f4b945f6a6416cc2524ba740b83cc9af25a upstream.

Most of these sizes and counts are capped at 256MB so the math doesn't
result in an integer overflow.  The "relocs" count needs to be checked
as well.  Otherwise on 32bit systems the calculation of "full_data"
could be wrong.

	full_data = data_len + relocs * sizeof(unsigned long);

Fixes: c995ee28 ("binfmt_flat: prevent kernel dammage from corrupted executable headers")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Nicolas Pitre <npitre@baylibre.com>
Link: https://lore.kernel.org/r/5be17f6c-5338-43be-91ef-650153b975cb@stanley.mountain


Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>