strscpy: reject buffer sizes larger than INT_MAX

strscpy: reject buffer sizes larger than INT_MAX

As already done for snprintf(), add a check in strscpy() for giant (i.e.
likely negative and/or miscalculated) copy sizes, WARN, and error out.

Link: http://lkml.kernel.org/r/201907260928.23DE35406@keescook
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Joe Perches <joe@perches.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Yann Droneaud <ydroneaud@opteya.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Stephen Kitt <steve@sk2.org>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>