Function ipcperm

freebsd/kern/sysv_ipc.c:89–154

* Check for IPC permission. * * Note: The MAC Framework does not require any modifications to the * ipcperm() function, as access control checks are performed throughout the * implementation of each primitive. Those entry point calls complement the * ipcperm() discertionary checks. Unlike file system discretionary access * control, the original create of an object is given the same rights

 * current owner.
 */
int
ipcperm(struct thread *td, struct ipc_perm *perm, int acc_mode)
{
	struct ucred *cred = td->td_ucred;
	int error, obj_mode, dac_granted, priv_granted;

	dac_granted = 0;
	if (cred->cr_uid == perm->cuid || cred->cr_uid == perm->uid) {
		obj_mode = perm->mode;
		dac_granted |= IPC_M;
	} else if (groupmember(perm->gid, cred) ||
	    groupmember(perm->cgid, cred)) {
		obj_mode = perm->mode;
		obj_mode <<= 3;
	} else {
		obj_mode = perm->mode;
		obj_mode <<= 6;
	}

	/*
	 * While the System V IPC permission model allows IPC_M to be
	 * granted, as part of the mode, our implementation requires
	 * privilege to adminster the object if not the owner or creator.
	 */
#if 0
	if (obj_mode & IPC_M)
		dac_granted |= IPC_M;
#endif
	if (obj_mode & IPC_R)
		dac_granted |= IPC_R;
	if (obj_mode & IPC_W)
		dac_granted |= IPC_W;

	/*
	 * Simple case: all required rights are granted by DAC.
	 */
	if ((dac_granted & acc_mode) == acc_mode)
		return (0);

	/*
	 * Privilege is required to satisfy the request.
	 */
	priv_granted = 0;
	if ((acc_mode & IPC_M) && !(dac_granted & IPC_M)) {
		error = priv_check(td, PRIV_IPC_ADMIN);
		if (error == 0)
			priv_granted |= IPC_M;
	}

	if ((acc_mode & IPC_R) && !(dac_granted & IPC_R)) {
		error = priv_check(td, PRIV_IPC_READ);
		if (error == 0)
			priv_granted |= IPC_R;
	}

	if ((acc_mode & IPC_W) && !(dac_granted & IPC_W)) {
		error = priv_check(td, PRIV_IPC_WRITE);
		if (error == 0)