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

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Message-ID: <20210412155830.GA19589@hoboy.vegasvil.org>
Date:   Mon, 12 Apr 2021 08:58:30 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     "chenjun (AM)" <chenjun102@...wei.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>, john.stultz@...aro.org,
        "Xiangrui (Euler)" <rui.xiang@...wei.com>
Subject: Re: [PATCH] time: Fix overwrite err unexpected in clock_adjtime32

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