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

[Peilin Ye]

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+03e343dbccf82a524...@syzkaller.appspotmail.com
Signed-off-by: Peilin Ye <yepeilin...@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