[patch 1/2] sys_alarm() unsigned signed conversion fixup

From: Thomas Gleixner
Date: Sun Mar 19 2006 - 14:59:55 EST



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 <tglx@xxxxxxxxxxxxx>

arch/ia64/ia32/sys_ia32.c | 14 +-------------
arch/mips/kernel/sysirix.c | 22 +---------------------
arch/x86_64/ia32/sys_ia32.c | 16 ++--------------
include/linux/time.h | 1 +
kernel/itimer.c | 37 +++++++++++++++++++++++++++++++++++++
kernel/timer.c | 14 +-------------
6 files changed, 43 insertions(+), 61 deletions(-)

Index: linux-2.6.16-rc6-updates/kernel/itimer.c
===================================================================
--- linux-2.6.16-rc6-updates.orig/kernel/itimer.c
+++ linux-2.6.16-rc6-updates/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 immidiate expiry.
+ */
+unsigned int alarm_setitimer(unsigned int seconds)
+{
+ struct itimerval it_new, it_old;
+
+#if BITS_PER_LONG < 64
+ if (seconds > (INT_MAX >> 1))
+ seconds = (INT_MAX >> 1);
+#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)
Index: linux-2.6.16-rc6-updates/arch/ia64/ia32/sys_ia32.c
===================================================================
--- linux-2.6.16-rc6-updates.orig/arch/ia64/ia32/sys_ia32.c
+++ linux-2.6.16-rc6-updates/arch/ia64/ia32/sys_ia32.c
@@ -1166,19 +1166,7 @@ put_tv32 (struct compat_timeval __user *
asmlinkage unsigned long
sys32_alarm (unsigned int seconds)
{
- struct itimerval it_new, it_old;
- unsigned int oldalarm;
-
- it_new.it_interval.tv_sec = it_new.it_interval.tv_usec = 0;
- it_new.it_value.tv_sec = seconds;
- it_new.it_value.tv_usec = 0;
- do_setitimer(ITIMER_REAL, &it_new, &it_old);
- oldalarm = it_old.it_value.tv_sec;
- /* ehhh.. 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_usec)
- oldalarm++;
- return oldalarm;
+ return alarm_setitimer(seconds);
}

/* Translations due to time_t size differences. Which affects all
Index: linux-2.6.16-rc6-updates/arch/mips/kernel/sysirix.c
===================================================================
--- linux-2.6.16-rc6-updates.orig/arch/mips/kernel/sysirix.c
+++ linux-2.6.16-rc6-updates/arch/mips/kernel/sysirix.c
@@ -645,27 +645,7 @@ static inline void getitimer_real(struct

asmlinkage unsigned int irix_alarm(unsigned int seconds)
{
- struct itimerval it_new, it_old;
- unsigned int oldalarm;
-
- if (!seconds) {
- getitimer_real(&it_old);
- del_timer(&current->real_timer);
- } else {
- it_new.it_interval.tv_sec = it_new.it_interval.tv_usec = 0;
- it_new.it_value.tv_sec = seconds;
- it_new.it_value.tv_usec = 0;
- do_setitimer(ITIMER_REAL, &it_new, &it_old);
- }
- oldalarm = it_old.it_value.tv_sec;
- /*
- * ehhh.. 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_usec)
- oldalarm++;
-
- return oldalarm;
+ return alarm_setitimer(seconds);
}

asmlinkage int irix_pause(void)
Index: linux-2.6.16-rc6-updates/arch/x86_64/ia32/sys_ia32.c
===================================================================
--- linux-2.6.16-rc6-updates.orig/arch/x86_64/ia32/sys_ia32.c
+++ linux-2.6.16-rc6-updates/arch/x86_64/ia32/sys_ia32.c
@@ -430,24 +430,12 @@ put_tv32(struct compat_timeval __user *o
return err;
}

-extern int do_setitimer(int which, struct itimerval *, struct itimerval *);
+extern unsigned int alarm_setitimer(unsigned int seconds);

asmlinkage long
sys32_alarm(unsigned int seconds)
{
- struct itimerval it_new, it_old;
- unsigned int oldalarm;
-
- it_new.it_interval.tv_sec = it_new.it_interval.tv_usec = 0;
- it_new.it_value.tv_sec = seconds;
- it_new.it_value.tv_usec = 0;
- do_setitimer(ITIMER_REAL, &it_new, &it_old);
- oldalarm = it_old.it_value.tv_sec;
- /* ehhh.. 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_usec)
- oldalarm++;
- return oldalarm;
+ return alarm_setitimer(seconds);
}

/* Translations due to time_t size differences. Which affects all
Index: linux-2.6.16-rc6-updates/kernel/timer.c
===================================================================
--- linux-2.6.16-rc6-updates.orig/kernel/timer.c
+++ linux-2.6.16-rc6-updates/kernel/timer.c
@@ -955,19 +955,7 @@ void do_timer(struct pt_regs *regs)
*/
asmlinkage unsigned long sys_alarm(unsigned int seconds)
{
- struct itimerval it_new, it_old;
- unsigned int oldalarm;
-
- it_new.it_interval.tv_sec = it_new.it_interval.tv_usec = 0;
- it_new.it_value.tv_sec = seconds;
- it_new.it_value.tv_usec = 0;
- do_setitimer(ITIMER_REAL, &it_new, &it_old);
- oldalarm = it_old.it_value.tv_sec;
- /* ehhh.. We can't return 0 if we have an alarm pending.. */
- /* And we'd better return too much than too little anyway */
- if ((!oldalarm && it_old.it_value.tv_usec) || it_old.it_value.tv_usec >= 500000)
- oldalarm++;
- return oldalarm;
+ return alarm_setitimer(seconds);
}

#endif
Index: linux-2.6.16-rc6-updates/include/linux/time.h
===================================================================
--- linux-2.6.16-rc6-updates.orig/include/linux/time.h
+++ linux-2.6.16-rc6-updates/include/linux/time.h
@@ -95,6 +95,7 @@ extern long do_utimes(int dfd, char __us
struct itimerval;
extern int do_setitimer(int which, struct itimerval *value,
struct itimerval *ovalue);
+extern unsigned int alarm_setitimer(unsigned int seconds);
extern int do_getitimer(int which, struct itimerval *value);
extern void getnstimeofday(struct timespec *tv);


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