linux-kernel - Re: [PATCH] time: Fix overwrite err unexpected in clock

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Date:   Tue, 13 Apr 2021 01:47:03 +0000
From:   "chenjun (AM)" <chenjun102@...wei.com>
To:     Richard Cochran <richardcochran@...il.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "john.stultz@...aro.org" <john.stultz@...aro.org>,
        "Xiangrui (Euler)" <rui.xiang@...wei.com>
Subject: Re: [PATCH] time: Fix overwrite err unexpected in clock_adjtime32

在 2021/4/12 23:58, Richard Cochran 写道:
> On Mon, Apr 12, 2021 at 02:52:11PM +0000, chenjun (AM) wrote:
>> 在 2021/4/12 22:20, Richard Cochran 写道:
>>> On Mon, Apr 12, 2021 at 12:45:51PM +0000, Chen Jun wrote:
>>>> the correct error is covered by put_old_timex32.
>>>
>>> Well, the non-negative return code (TIME_OK, TIME_INS, etc) is
>>> clobbered by put_old_timex32().
>>>
>>>> Fixes: f1f1d5ebd10f ("posix-timers: Introduce a syscall for clock tuning.")
>>>
>>> This is not the correct commit for the "Fixes" tag.  Please find the
>>> actual commit that introduced the issue.
>>>
>>> In commit f1f1d5ebd10f the code looked like this...
>>>
>>> 	long compat_sys_clock_adjtime(clockid_t which_clock,
>>> 			struct compat_timex __user *utp)
>>> 	{
>>> 		struct timex txc;
>>> 		mm_segment_t oldfs;
>>> 		int err, ret;
>>> 	
>>> 		err = compat_get_timex(&txc, utp);
>>> 		if (err)
>>> 			return err;
>>> 	
>>> 		oldfs = get_fs();
>>> 		set_fs(KERNEL_DS);
>>> 		ret = sys_clock_adjtime(which_clock, (struct timex __user *) &txc);
>>> 		set_fs(oldfs);
>>> 	
>>> 		err = compat_put_timex(utp, &txc);
>>> 		if (err)
>>> 			return err;
>>> 	
>>> 		return ret;
>>> 	}
> 
> Look at the code ^^^
> 
>> The implement of clock_adjtime32 is similar to compat_sys_clock_adjtime.
>> And I think f1f1d5ebd10 introduced the problem actually.
> 
> See how 'ret' and 'err' are two separate variables?  It makes a difference.
> 
> Thanks,
> Richard
> 

Oh, yee.. Very thanks.

3a4d44b616 ("ntp: Move adjtimex related compat syscalls to native 
counterparts") made the change.

-- 
Regards
Chen Jun