[PATCH] select: fix returned timeval

With David Woodhouse <dwmw2@infradead.org>

select() presently has a habit of increasing the value of the user's
`timeout' argument on return.

We were writing back a timeout larger than the original.  We _deliberately_
round up, since we know we must wait at _least_ as long as the caller asks
us to.

The patch adds a couple of helper functions for magnitude comparison of
timespecs and of timevals, and uses them to prevent the various poll and
select functions from returning a timeout which is larger than the one which
was passed in.

The patch also fixes a bug in compat_sys_pselect7(): it was adding the new
timeout value to the old one and was returning that.  It should just return
the new timeout value.

(We have various handy timespec/timeval-to-from-nsec conversion functions in
time.h.  But this code open-codes it all).

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Andi Kleen <ak@muc.de>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: george anzinger <george@mvista.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/include/linux/compat.h b/include/linux/compat.h
index f9ca534787e..c9ab2a26348 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -161,5 +161,25 @@ int copy_siginfo_to_user32(struct compat_siginfo __user *to, siginfo_t *from);
 int get_compat_sigevent(struct sigevent *event,
 		const struct compat_sigevent __user *u_event);
 
+static inline int compat_timeval_compare(struct compat_timeval *lhs,
+					struct compat_timeval *rhs)
+{
+	if (lhs->tv_sec < rhs->tv_sec)
+		return -1;
+	if (lhs->tv_sec > rhs->tv_sec)
+		return 1;
+	return lhs->tv_usec - rhs->tv_usec;
+}
+
+static inline int compat_timespec_compare(struct compat_timespec *lhs,
+					struct compat_timespec *rhs)
+{
+	if (lhs->tv_sec < rhs->tv_sec)
+		return -1;
+	if (lhs->tv_sec > rhs->tv_sec)
+		return 1;
+	return lhs->tv_nsec - rhs->tv_nsec;
+}
+
 #endif /* CONFIG_COMPAT */
 #endif /* _LINUX_COMPAT_H */