2020-07-12 21:06:10

by Peilin Ye

Subject: [Linux-kernel-mentees] [PATCH net] qrtr: Fix ZERO_SIZE_PTR deref in qrtr_tun_write_iter()

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: [email protected]
Signed-off-by: Peilin Ye <[email protected]>
---
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;
--
2.25.1

2020-07-12 21:37:15

by Eric Biggers

Subject: Re: [Linux-kernel-mentees] [PATCH net] qrtr: Fix ZERO_SIZE_PTR deref in qrtr_tun_write_iter()

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: [email protected]
> Signed-off-by: Peilin Ye <[email protected]>
> ---
> 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 <[email protected]>
Date: Tue Jun 30 14:46:15 2020 +0300

net: qrtr: Fix an out of bounds read qrtr_endpoint_post()

2020-07-13 09:15:09

by Dan Carpenter

Subject: Re: [Linux-kernel-mentees] [PATCH net] qrtr: Fix ZERO_SIZE_PTR deref in qrtr_tun_write_iter()

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: [email protected]
> > Signed-off-by: Peilin Ye <[email protected]>
> > ---
> > 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 <[email protected]>
> 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