kernel: kexec: copy user-array safely

Currently, there is no overflow-check with memdup_user().

Use the new function memdup_array_user() instead of memdup_user() for
duplicating the user-space array safely.

Suggested-by: David Airlie <[email protected]>
Signed-off-by: Philipp Stanner <[email protected]>
Acked-by: Baoquan He <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Reviewed-by: Zack Rusin <[email protected]>
Signed-off-by: Dave Airlie <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: Philipp Stanner

kernel/kexec.c

@@ -247,7 +247,7 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
 		((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))
 		return -EINVAL;
 
-	ksegments = memdup_user(segments, nr_segments * sizeof(ksegments[0]));
+	ksegments = memdup_array_user(segments, nr_segments, sizeof(ksegments[0]));
 	if (IS_ERR(ksegments))
 		return PTR_ERR(ksegments);