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From:   Peilin Ye <yepeilin.cs@gmail.com>
To:     "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>
Cc:     Peilin Ye <yepeilin.cs@gmail.com>,
        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: [Linux-kernel-mentees] [PATCH net] qrtr: Fix ZERO_SIZE_PTR deref in qrtr_tun_write_iter()
Date:   Sun, 12 Jul 2020 17:03:00 -0400
Message-Id: <20200712210300.200399-1-yepeilin.cs@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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;
-- 
2.25.1