From: Andrew Morton <akpm@linux-foundation.org>
To: Chen Gang <gang.chen@asianux.com>
Cc: Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>,
jmoyer@redhat.com, Jens Axboe <axboe@kernel.dk>,
linux-mm@kvack.org
Subject: Re: [PATCH] mm/backing-dev.c: check user buffer length before copy data to the related user buffer.
Date: Tue, 20 Aug 2013 20:45:50 -0700 [thread overview]
Message-ID: <20130820204550.356e13b5.akpm@linux-foundation.org> (raw)
In-Reply-To: <52143568.30708@asianux.com>
On Wed, 21 Aug 2013 11:35:04 +0800 Chen Gang <gang.chen@asianux.com> wrote:
> On 08/21/2013 07:29 AM, Andrew Morton wrote:
> > On Tue, 20 Aug 2013 11:23:24 +0800 Chen Gang <gang.chen@asianux.com> wrote:
> >
> >> '*lenp' may be less than "sizeof(kbuf)", need check it before the next
> >> copy_to_user().
> >>
> >> pdflush_proc_obsolete() is called by sysctl which 'procname' is
> >> "nr_pdflush_threads", if the user passes buffer length less than
> >> "sizeof(kbuf)", it will cause issue.
> >>
> >> ...
> >>
> >> --- a/mm/backing-dev.c
> >> +++ b/mm/backing-dev.c
> >> @@ -649,7 +649,7 @@ int pdflush_proc_obsolete(struct ctl_table *table, int write,
> >> {
> >> char kbuf[] = "0\n";
> >>
> >> - if (*ppos) {
> >> + if (*ppos || *lenp < sizeof(kbuf)) {
> >> *lenp = 0;
> >> return 0;
> >> }
> >
> > Well sort-of. If userspace opens /proc/sys/vm/nr_pdflush_threads and
> > then does a series of one-byte reads, the kernel should return "0" on the
> > first read, "\n" on the second and then EOF.
> >
>
> Excuse me for my English, I guess your meaning is
>
> "this patch is OK, but can be improvement"
>
> Is it correct ?
Not really. I was pointing out that the patched code doesn't correctly
implement read(1) behavior. But that is true of many other procfs
files, so I suggest we not attempt to address the problem for this
procfs file.
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next prev parent reply other threads:[~2013-08-21 3:46 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-20 3:23 [PATCH] mm/backing-dev.c: check user buffer length before copy data to the related user buffer Chen Gang
2013-08-20 15:28 ` Jan Kara
2013-08-21 2:28 ` Chen Gang
2013-08-20 23:29 ` Andrew Morton
2013-08-21 3:35 ` Chen Gang
2013-08-21 3:45 ` Andrew Morton [this message]
2013-08-21 3:56 ` Chen Gang
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