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From: Dan Carpenter <dan.carpenter@oracle.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Peilin Ye <yepeilin.cs@gmail.com>,
	"David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Navid Emamdoost <navid.emamdoost@gmail.com>,
	Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com,
	linux-kernel-mentees@lists.linuxfoundation.org,
	linux-kernel@vger.kernel.org
Subject: Re: [Linux-kernel-mentees] [PATCH net] qrtr: Fix ZERO_SIZE_PTR deref in qrtr_tun_write_iter()
Date: Mon, 13 Jul 2020 12:13:29 +0300	[thread overview]
Message-ID: <20200713091329.GP2571@kadam> (raw)
In-Reply-To: <20200712213631.GA809@sol.localdomain>

On Sun, Jul 12, 2020 at 02:36:31PM -0700, Eric Biggers wrote:
> On Sun, Jul 12, 2020 at 05:03:00PM -0400, Peilin Ye wrote:
> > qrtr_tun_write_iter() is dereferencing `ZERO_SIZE_PTR`s when `from->count`
> > equals to zero. Fix it by rejecting zero-length kzalloc() requests.
> > 
> > This patch fixes the following syzbot bug:
> > 
> >     https://syzkaller.appspot.com/bug?id=f56bbe6668873ee245986bbd23312b895fa5a50a
> > 
> > Reported-by: syzbot+03e343dbccf82a5242a2@syzkaller.appspotmail.com
> > Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
> > ---
> >  net/qrtr/tun.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/net/qrtr/tun.c b/net/qrtr/tun.c
> > index 15ce9b642b25..5465e94ba8e5 100644
> > --- a/net/qrtr/tun.c
> > +++ b/net/qrtr/tun.c
> > @@ -80,6 +80,9 @@ static ssize_t qrtr_tun_write_iter(struct kiocb *iocb, struct iov_iter *from)
> >  	ssize_t ret;
> >  	void *kbuf;
> >  
> > +	if (!len)
> > +		return -EINVAL;
> > +
> >  	kbuf = kzalloc(len, GFP_KERNEL);
> >  	if (!kbuf)
> >  		return -ENOMEM;
> 
> Wasn't this already fixed by:
> 
>     commit 8ff41cc21714704ef0158a546c3c4d07fae2c952
>     Author: Dan Carpenter <dan.carpenter@oracle.com>
>     Date:   Tue Jun 30 14:46:15 2020 +0300
> 
>         net: qrtr: Fix an out of bounds read qrtr_endpoint_post()


Yep.  If you're using kmalloc() you can allocate a zero byte buffer but
you just can't access the array.  for (i = 0; i < 0; i++) works.

It's interesting because at the time, I wrote the patch I thought "len"
probably couldn't be zero but I just checked it for completeness and
readability.

regards,
dan carpenter

WARNING: multiple messages have this Message-ID (diff)
From: Dan Carpenter <dan.carpenter@oracle.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org,
	"David S . Miller" <davem@davemloft.net>,
	Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
	netdev@vger.kernel.org, Jakub Kicinski <kuba@kernel.org>,
	linux-kernel-mentees@lists.linuxfoundation.org,
	Peilin Ye <yepeilin.cs@gmail.com>,
	Navid Emamdoost <navid.emamdoost@gmail.com>
Subject: Re: [Linux-kernel-mentees] [PATCH net] qrtr: Fix ZERO_SIZE_PTR deref in qrtr_tun_write_iter()
Date: Mon, 13 Jul 2020 12:13:29 +0300	[thread overview]
Message-ID: <20200713091329.GP2571@kadam> (raw)
In-Reply-To: <20200712213631.GA809@sol.localdomain>

On Sun, Jul 12, 2020 at 02:36:31PM -0700, Eric Biggers wrote:
> On Sun, Jul 12, 2020 at 05:03:00PM -0400, Peilin Ye wrote:
> > qrtr_tun_write_iter() is dereferencing `ZERO_SIZE_PTR`s when `from->count`
> > equals to zero. Fix it by rejecting zero-length kzalloc() requests.
> > 
> > This patch fixes the following syzbot bug:
> > 
> >     https://syzkaller.appspot.com/bug?id=f56bbe6668873ee245986bbd23312b895fa5a50a
> > 
> > Reported-by: syzbot+03e343dbccf82a5242a2@syzkaller.appspotmail.com
> > Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
> > ---
> >  net/qrtr/tun.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/net/qrtr/tun.c b/net/qrtr/tun.c
> > index 15ce9b642b25..5465e94ba8e5 100644
> > --- a/net/qrtr/tun.c
> > +++ b/net/qrtr/tun.c
> > @@ -80,6 +80,9 @@ static ssize_t qrtr_tun_write_iter(struct kiocb *iocb, struct iov_iter *from)
> >  	ssize_t ret;
> >  	void *kbuf;
> >  
> > +	if (!len)
> > +		return -EINVAL;
> > +
> >  	kbuf = kzalloc(len, GFP_KERNEL);
> >  	if (!kbuf)
> >  		return -ENOMEM;
> 
> Wasn't this already fixed by:
> 
>     commit 8ff41cc21714704ef0158a546c3c4d07fae2c952
>     Author: Dan Carpenter <dan.carpenter@oracle.com>
>     Date:   Tue Jun 30 14:46:15 2020 +0300
> 
>         net: qrtr: Fix an out of bounds read qrtr_endpoint_post()


Yep.  If you're using kmalloc() you can allocate a zero byte buffer but
you just can't access the array.  for (i = 0; i < 0; i++) works.

It's interesting because at the time, I wrote the patch I thought "len"
probably couldn't be zero but I just checked it for completeness and
readability.

regards,
dan carpenter
_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

  reply	other threads:[~2020-07-13  9:13 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-12 21:03 [Linux-kernel-mentees] [PATCH net] qrtr: Fix ZERO_SIZE_PTR deref in qrtr_tun_write_iter() Peilin Ye
2020-07-12 21:03 ` Peilin Ye
2020-07-12 21:36 ` Eric Biggers
2020-07-12 21:36   ` Eric Biggers
2020-07-13  9:13   ` Dan Carpenter [this message]
2020-07-13  9:13     ` Dan Carpenter

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