itimers: Fix racy writes to cpu_itimer fields

incr_error and error fields of struct cpu_itimer are used when calculating
next timer tick in check_cpu_itimers() and should not be modified without
tsk->sighand->siglock taken.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
LKML-Reference: <1253802903-979-1-git-send-email-sgruszka@redhat.com> 
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 5 insertions, 2 deletions

diff --git a/kernel/itimer.c b/kernel/itimer.c
index b03451ede528..d802883153da 100644
--- a/kernel/itimer.c
+++ b/kernel/itimer.c
@@ -146,6 +146,7 @@ static void set_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
 {
         cputime_t cval, nval, cinterval, ninterval;
         s64 ns_ninterval, ns_nval;
+        u32 error, incr_error;
         struct cpu_itimer *it = &tsk->signal->it[clock_id];
 
         nval = timeval_to_cputime(&value->it_value);
@@ -153,8 +154,8 @@ static void set_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
         ninterval = timeval_to_cputime(&value->it_interval);
         ns_ninterval = timeval_to_ns(&value->it_interval);
 
-        it->incr_error = cputime_sub_ns(ninterval, ns_ninterval);
-        it->error = cputime_sub_ns(nval, ns_nval);
+        error = cputime_sub_ns(nval, ns_nval);
+        incr_error = cputime_sub_ns(ninterval, ns_ninterval);
 
         spin_lock_irq(&tsk->sighand->siglock);
 
@@ -168,6 +169,8 @@ static void set_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
         }
         it->expires = nval;
         it->incr = ninterval;
+        it->error = error;
+        it->incr_error = incr_error;
         trace_itimer_state(clock_id == CPUCLOCK_VIRT ?
                            ITIMER_VIRTUAL : ITIMER_PROF, value, nval);