FreeBSD: Fix RLIMIT_FSIZE handling for block cloning

ZFS implements copy_file_range(2) using block cloning when possible.
This implementation must respect the RLIMIT_FSIZE limit.

zfs_clone_range() already checks the limit, so it is safe to remove this
check in zfs_freebsd_copy_file_range().  Moreover, the removed check
produces false positives: the length passed to copy_file_range(2) may be
larger than the input file size; as the man page notes, "for best
performance, call copy_file_range() with the largest len value
possible."  In particular, some existing code passes SSIZE_MAX there.

The check in zfs_clone_range() clamps the length to the input file's
size before checking, but the removed check uses the caller supplied
length, so something like

$ echo a > /tmp/foo
$ limits -f 1024 cat /tmp/foo > /tmp/bar

fails because FreeBSD's cat(1) uses copy_file_range(2) in the manner
described above.

Reported-by: Philip Paeps <[email protected]>
Signed-off-by: Mark Johnston <[email protected]>

Reviewed-by: Alexander Motin <[email protected]>
Reviewed-by: Allan Jude <[email protected]>
Reviewed-by: Tino Reichardt <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>

module/os/freebsd/zfs/zfs_vnops_os.c

@@ -6072,7 +6072,6 @@ zfs_freebsd_copy_file_range(struct vop_copy_file_range_args *ap)
 	struct vnode *invp = ap->a_invp;
 	struct vnode *outvp = ap->a_outvp;
 	struct mount *mp;
-	struct uio io;
 	int error;
 	uint64_t len = *ap->a_lenp;
 
@@ -6120,12 +6119,6 @@ zfs_freebsd_copy_file_range(struct vop_copy_file_range_args *ap)
 		goto out_locked;
 #endif
 
-	io.uio_offset = *ap->a_outoffp;
-	io.uio_resid = *ap->a_lenp;
-	error = vn_rlimit_fsize(outvp, &io, ap->a_fsizetd);
-	if (error != 0)
-		goto out_locked;
-
 	error = zfs_clone_range(VTOZ(invp), ap->a_inoffp, VTOZ(outvp),
 	    ap->a_outoffp, &len, ap->a_outcred);
 	if (error == EXDEV || error == EAGAIN || error == EINVAL ||