From c08b8a49100715b20e6f7c997e992428b5e06078 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 25 Mar 2006 03:06:33 -0800 Subject: [PATCH] sys_alarm() unsigned signed conversion fixup alarm() calls the kernel with an unsigend int timeout in seconds. The value is stored in the tv_sec field of a struct timeval to setup the itimer. The tv_sec field of struct timeval is of type long, which causes the tv_sec value to be negative on 32 bit machines if seconds > INT_MAX. Before the hrtimer merge (pre 2.6.16) such a negative value was converted to the maximum jiffies timeout by the timeval_to_jiffies conversion. It's not clear whether this was intended or just happened to be done by the timeval_to_jiffies code. hrtimers expect a timeval in canonical form and treat a negative timeout as already expired. This breaks the legitimate usage of alarm() with a timeout value > INT_MAX seconds. For 32 bit machines it is therefor necessary to limit the internal seconds value to avoid API breakage. Instead of doing this in all implementations of sys_alarm the duplicated sys_alarm code is moved into a common function in itimer.c Signed-off-by: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/itimer.c | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) (limited to 'kernel/itimer.c') diff --git a/kernel/itimer.c b/kernel/itimer.c index 379be2f..a2dc375 100644 --- a/kernel/itimer.c +++ b/kernel/itimer.c @@ -226,6 +226,43 @@ again: return 0; } +/** + * alarm_setitimer - set alarm in seconds + * + * @seconds: number of seconds until alarm + * 0 disables the alarm + * + * Returns the remaining time in seconds of a pending timer or 0 when + * the timer is not active. + * + * On 32 bit machines the seconds value is limited to (INT_MAX/2) to avoid + * negative timeval settings which would cause immediate expiry. + */ +unsigned int alarm_setitimer(unsigned int seconds) +{ + struct itimerval it_new, it_old; + +#if BITS_PER_LONG < 64 + if (seconds > INT_MAX) + seconds = INT_MAX; +#endif + it_new.it_value.tv_sec = seconds; + it_new.it_value.tv_usec = 0; + it_new.it_interval.tv_sec = it_new.it_interval.tv_usec = 0; + + do_setitimer(ITIMER_REAL, &it_new, &it_old); + + /* + * We can't return 0 if we have an alarm pending ... And we'd + * better return too much than too little anyway + */ + if ((!it_old.it_value.tv_sec && it_old.it_value.tv_usec) || + it_old.it_value.tv_usec >= 500000) + it_old.it_value.tv_sec++; + + return it_old.it_value.tv_sec; +} + asmlinkage long sys_setitimer(int which, struct itimerval __user *value, struct itimerval __user *ovalue) -- cgit v1.1