chmod fails to tell about bum arguments under 4.1bsd (with fix)-REPOST

[Arthur David Olson]

Defendant--	/sys/sys/sy4.c

Charge--	The "chmod" function in /sys/sys/sys4.c fails to
		let the invoking process know about bum arguments.

Evidence--	As a "normal" (as distinct from "super") user type:
			cp /dev/null testing123
			chmod +t testing123
			chmod 60666 testing123

		The first chmod command asks for the sticky bit to be set,
		which only the super user is supposed to be able to do.
		The sticky bit is not set--but no diagnostic is produced.

		The second chmod command tries to set a nonsensical mode.
		The nonsense bits are silently ignored.

Verdict--	Not guilty by reason of insanity.

Sentence--	Here are the lines that show how to fix "/sys/sys/sys4.c":

	#ifdef OLDVERSION
		ip->i_mode &= ~07777;
		if (u.u_uid)
			uap->fmode &= ~ISVTX;
		ip->i_mode |= uap->fmode&07777;
		ip->i_flag |= ICHG;
	#else
		if ((uap->fmode & ~07777) != 0 &&
			(uap->fmode & ~07777) != (ip->i_mode & ~07777))
				u.u_error = EINVAL;
		else if (u.u_uid && (uap->fmode & ISVTX) != 0)
				u.u_error = EPERM;
		else {
			ip->i_mode &= ~07777;
			ip->i_mode |= uap->fmode & 07777;
			ip->i_flag |= ICHG;
		}
	#endif

		The fix is done in such a way that code like:

	#include <sys/types.h>
	#include <sys/stat.h>

	main()
	{
		struct stat	s;

		stat("testing123", &s);
		chmod("testing123", s.st_mode | 01);
	}
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