From: Alexander Potapenko <glider@google.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: syzbot <syzbot+af962bf9e7e27bccd025@syzkaller.appspotmail.com>,
len.brown@intel.com, LKML <linux-kernel@vger.kernel.org>,
Linux PM <linux-pm@vger.kernel.org>, Pavel Machek <pavel@ucw.cz>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>
Subject: Re: KMSAN: uninit-value in snapshot_compat_ioctl
Date: Fri, 13 Mar 2020 15:10:45 +0100 [thread overview]
Message-ID: <CAG_fn=U=ti=YB553DCC-_gmbiHR6=xBG4HQbyc54R3sdGCY=LA@mail.gmail.com> (raw)
In-Reply-To: <20200309181154.GB1073@sol.localdomain>
On Mon, Mar 9, 2020 at 7:11 PM Eric Biggers <ebiggers@kernel.org> wrote:
>
> On Mon, Mar 09, 2020 at 12:53:28PM +0100, 'Alexander Potapenko' via syzkaller-bugs wrote:
> > > > Looks like a KMSAN false positive? As far as I can tell, the memory is being
> > > > initialized by put_user() called under set_fs(KERNEL_DS).
> >
> > Why? put_user() doesn't write to kernel memory, instead it copies a
> > value to the userspace.
> > That's why KMSAN performs kmsan_check_memory() on it.
> > It would actually be better if KMSAN printed an kernel-infoleak warning instead.
>
> When under set_fs(KERNEL_DS), the userspace access functions like put_user() and
> copy_to_user() can write to kernel memory. It's discouraged and people have
> been trying to get rid of uses of set_fs(), but a lot still remain, since
> sometimes it's useful to allow code to operate on both user and kernel memory.
> A common example is kernel_read().
Ah, you're right. We can simply check that the target address is in
the userspace before actually reporting the error.
prev parent reply other threads:[~2020-03-13 14:11 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-26 15:59 KMSAN: uninit-value in snapshot_compat_ioctl syzbot
2020-03-07 23:54 ` Eric Biggers
2020-03-08 3:24 ` Eric Biggers
2020-03-08 3:27 ` [PATCH] PM / hibernate: Remove unnecessary compat ioctl overrides Eric Biggers
2020-03-14 10:57 ` Rafael J. Wysocki
2020-03-09 11:53 ` KMSAN: uninit-value in snapshot_compat_ioctl Alexander Potapenko
2020-03-09 18:11 ` Eric Biggers
2020-03-13 14:10 ` Alexander Potapenko [this message]
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