Re: [PATCH 2/5] hrtimer_nanosleep: fix *rmtp handling

From: Oleg Nesterov
Date: Fri Feb 01 2008 - 09:26:52 EST

(Andrew, the same patch, but re-diffed without the first one in series).


[PATCH 2/5] hrtimer_nanosleep: fix *rmtp handling

Spotted by Pavel Emelyanov and Alexey Dobriyan.

hrtimer_nanosleep() sets restart_block->arg1 = rmtp, but this rmtp points to
the local variable which lives in the caller's stack frame. This means that
if sys_restart_syscall() actually happens and it is interrupted as well, we
don't update the user-space variable, but write into the already dead stack
frame.

Change the callers to pass "__user *rmtp" to hrtimer_nanosleep(), and change
hrtimer_nanosleep() to use copy_to_user() to actually update *rmtp.

Small problem remains. man 2 nanosleep states that *rtmp should be written if
nanosleep() was interrupted (it says nothing whether it is OK to update *rmtp
if nanosleep returns 0), but (with or without this patch) we can dirty *rem
even if nanosleep() returns 0.

NOTE: this patch doesn't change compat_sys_nanosleep(), because it has other
bugs. Fixed by the next patch.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

include/linux/hrtimer.h | 2 -
kernel/hrtimer.c | 51 +++++++++++++++++++++++++-----------------------
kernel/posix-timers.c | 14 +------------
3 files changed, 30 insertions(+), 37 deletions(-)

--- MM/include/linux/hrtimer.h~HRT_RMTP 2008-01-27 17:07:39.000000000 +0300
+++ MM/include/linux/hrtimer.h 2008-01-31 14:01:53.000000000 +0300
@@ -313,7 +313,7 @@ static inline u64 hrtimer_forward_now(st

/* Precise sleep: */
extern long hrtimer_nanosleep(struct timespec *rqtp,
- struct timespec *rmtp,
+ struct timespec __user *rmtp,
const enum hrtimer_mode mode,
const clockid_t clockid);
extern long hrtimer_nanosleep_restart(struct restart_block *restart_block);
--- MM/kernel/hrtimer.c~HRT_RMTP 2008-02-01 13:43:52.000000000 +0300
+++ MM/kernel/hrtimer.c 2008-02-01 13:56:44.000000000 +0300
@@ -1317,11 +1317,26 @@ static int __sched do_nanosleep(struct h
return t->task == NULL;
}

+static int update_rmtp(struct hrtimer *timer, struct timespec __user *rmtp)
+{
+ struct timespec rmt;
+ ktime_t rem;
+
+ rem = ktime_sub(timer->expires, timer->base->get_time());
+ if (rem.tv64 <= 0)
+ return 0;
+ rmt = ktime_to_timespec(rem);
+
+ if (copy_to_user(rmtp, &rmt, sizeof(*rmtp)))
+ return -EFAULT;
+
+ return 1;
+}
+
long __sched hrtimer_nanosleep_restart(struct restart_block *restart)
{
struct hrtimer_sleeper t;
- struct timespec *rmtp;
- ktime_t time;
+ struct timespec __user *rmtp;

restart->fn = do_no_restart_syscall;

@@ -1331,12 +1346,11 @@ long __sched hrtimer_nanosleep_restart(s
if (do_nanosleep(&t, HRTIMER_MODE_ABS))
return 0;

- rmtp = (struct timespec *)restart->arg1;
+ rmtp = (struct timespec __user *)restart->arg1;
if (rmtp) {
- time = ktime_sub(t.timer.expires, t.timer.base->get_time());
- if (time.tv64 <= 0)
- return 0;
- *rmtp = ktime_to_timespec(time);
+ int ret = update_rmtp(&t.timer, rmtp);
+ if (ret <= 0)
+ return ret;
}

restart->fn = hrtimer_nanosleep_restart;
@@ -1345,12 +1359,11 @@ long __sched hrtimer_nanosleep_restart(s
return -ERESTART_RESTARTBLOCK;
}

-long hrtimer_nanosleep(struct timespec *rqtp, struct timespec *rmtp,
+long hrtimer_nanosleep(struct timespec *rqtp, struct timespec __user *rmtp,
const enum hrtimer_mode mode, const clockid_t clockid)
{
struct restart_block *restart;
struct hrtimer_sleeper t;
- ktime_t rem;

hrtimer_init(&t.timer, clockid, mode);
t.timer.expires = timespec_to_ktime(*rqtp);
@@ -1362,10 +1375,9 @@ long hrtimer_nanosleep(struct timespec *
return -ERESTARTNOHAND;

if (rmtp) {
- rem = ktime_sub(t.timer.expires, t.timer.base->get_time());
- if (rem.tv64 <= 0)
- return 0;
- *rmtp = ktime_to_timespec(rem);
+ int ret = update_rmtp(&t.timer, rmtp);
+ if (ret <= 0)
+ return ret;
}

restart = &current_thread_info()->restart_block;
@@ -1381,8 +1393,7 @@ long hrtimer_nanosleep(struct timespec *
asmlinkage long
sys_nanosleep(struct timespec __user *rqtp, struct timespec __user *rmtp)
{
- struct timespec tu, rmt;
- int ret;
+ struct timespec tu;

if (copy_from_user(&tu, rqtp, sizeof(tu)))
return -EFAULT;
@@ -1390,15 +1401,7 @@ sys_nanosleep(struct timespec __user *rq
if (!timespec_valid(&tu))
return -EINVAL;

- ret = hrtimer_nanosleep(&tu, rmtp ? &rmt : NULL, HRTIMER_MODE_REL,
- CLOCK_MONOTONIC);
-
- if (ret && rmtp) {
- if (copy_to_user(rmtp, &rmt, sizeof(*rmtp)))
- return -EFAULT;
- }
-
- return ret;
+ return hrtimer_nanosleep(&tu, rmtp, HRTIMER_MODE_REL, CLOCK_MONOTONIC);
}

/*
--- MM/kernel/posix-timers.c~HRT_RMTP 2008-01-27 17:07:40.000000000 +0300
+++ MM/kernel/posix-timers.c 2008-02-01 13:18:51.000000000 +0300
@@ -982,20 +982,10 @@ sys_clock_getres(const clockid_t which_c
static int common_nsleep(const clockid_t which_clock, int flags,
struct timespec *tsave, struct timespec __user *rmtp)
{
- struct timespec rmt;
- int ret;
-
- ret = hrtimer_nanosleep(tsave, rmtp ? &rmt : NULL,
+ return hrtimer_nanosleep(tsave, rmtp,
flags & TIMER_ABSTIME ?
- HRTIMER_MODE_ABS : HRTIMER_MODE_REL,
+ HRTIMER_MODE_ABS : HRTIMER_MODE_REL,
which_clock);
-
- if (ret && rmtp) {
- if (copy_to_user(rmtp, &rmt, sizeof(*rmtp)))
- return -EFAULT;
- }
-
- return ret;
}

asmlinkage long

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