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

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Message-ID: <0aacd0e17515458483653f570b1efd2d@huawei.com>
Date:   Mon, 12 Apr 2021 14:52:11 +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>,
        "johnstul@...ibm.com" <johnstul@...ibm.com>,
        "Xiangrui (Euler)" <rui.xiang@...wei.com>
Subject: Re: [PATCH] time: Fix overwrite err unexpected in clock_adjtime32

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;
> 	}
> 

f1f1d5ebd10:
Introduce compat_sys_clock_adjtime

62a6fa97684:
rename compat_sys_clock_adjtime to COMPAT_SYSCALL_DEFINE2(clock_adjtime

3a4d44b6162:
move COMPAT_SYSCALL_DEFINE2(clock_adjtime from kernel/compat.c to 
kernel/time/posix-timers.c

8dabe7245bb:
COMPAT_SYSCALL_DEFINE2(clock_adjtime, ..
-> SYSCALL_DEFINE2(clock_adjtime32, ..

The implement of clock_adjtime32 is similar to compat_sys_clock_adjtime. 
And I think f1f1d5ebd10 introduced the problem actually.

> Thanks,
> Richard
> 
> 
> 
>> Signed-off-by: Chen Jun <chenjun102@...wei.com>
>> ---
>>   kernel/time/posix-timers.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
>> index bf540f5a..dd5697d 100644
>> --- a/kernel/time/posix-timers.c
>> +++ b/kernel/time/posix-timers.c
>> @@ -1191,8 +1191,8 @@ SYSCALL_DEFINE2(clock_adjtime32, clockid_t, which_clock,
>>   
>>   	err = do_clock_adjtime(which_clock, &ktx);
>>   
>> -	if (err >= 0)
>> -		err = put_old_timex32(utp, &ktx);
>> +	if (err >= 0 && put_old_timex32(utp, &ktx))
>> +		return -EFAULT;
>>   
>>   	return err;
>>   }
>> -- 
>> 2.9.4
>>
> 


-- 
Regards
Chen Jun