libceph: store timeouts in jiffies, verify user input

There are currently three libceph-level timeouts that the user can
specify on mount: mount_timeout, osd_idle_ttl and osdkeepalive.  All of
these are in seconds and no checking is done on user input: negative
values are accepted, we multiply them all by HZ which may or may not
overflow, arbitrarily large jiffies then get added together, etc.

There is also a bug in the way mount_timeout=0 is handled.  It's
supposed to mean "infinite timeout", but that's not how wait.h APIs
treat it and so __ceph_open_session() for example will busy loop
without much chance of being interrupted if none of ceph-mons are
there.

Fix all this by verifying user input, storing timeouts capped by
msecs_to_jiffies() in jiffies and using the new ceph_timeout_jiffies()
helper for all user-specified waits to handle infinite timeouts
correctly.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Alex Elder <elder@linaro.org>

fs/ceph/dir.c

@@ -1259,8 +1259,8 @@ static int ceph_dir_fsync(struct file *file, loff_t start, loff_t end,
 		     inode, req->r_tid, last_tid);
 		if (req->r_timeout) {
 			unsigned long time_left = wait_for_completion_timeout(
-							&req->r_safe_completion,
-							req->r_timeout);
+					&req->r_safe_completion,
+					ceph_timeout_jiffies(req->r_timeout));
 			if (time_left > 0)
 				ret = 0;
 			else