linux-kernel - [PATCH 4.19 42/48] net: qrtr: fix len of skb_put_padto in qrtr_node

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Date:   Thu, 19 Mar 2020 14:04:24 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Carl Huang <cjhuang@...eaurora.org>,
        Wen Gong <wgong@...eaurora.org>,
        Doug Anderson <dianders@...omium.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.19 42/48] net: qrtr: fix len of skb_put_padto in qrtr_node_enqueue

From: Carl Huang <cjhuang@...eaurora.org>

commit ce57785bf91b1ceaef4f4bffed8a47dc0919c8da upstream.

The len used for skb_put_padto is wrong, it need to add len of hdr.

In qrtr_node_enqueue, local variable size_t len is assign with
skb->len, then skb_push(skb, sizeof(*hdr)) will add skb->len with
sizeof(*hdr), so local variable size_t len is not same with skb->len
after skb_push(skb, sizeof(*hdr)).

Then the purpose of skb_put_padto(skb, ALIGN(len, 4)) is to add add
pad to the end of the skb's data if skb->len is not aligned to 4, but
unfortunately it use len instead of skb->len, at this line, skb->len
is 32 bytes(sizeof(*hdr)) more than len, for example, len is 3 bytes,
then skb->len is 35 bytes(3 + 32), and ALIGN(len, 4) is 4 bytes, so
__skb_put_padto will do nothing after check size(35) < len(4), the
correct value should be 36(sizeof(*hdr) + ALIGN(len, 4) = 32 + 4),
then __skb_put_padto will pass check size(35) < len(36) and add 1 byte
to the end of skb's data, then logic is correct.

function of skb_push:
void *skb_push(struct sk_buff *skb, unsigned int len)
{
	skb->data -= len;
	skb->len  += len;
	if (unlikely(skb->data < skb->head))
		skb_under_panic(skb, len, __builtin_return_address(0));
	return skb->data;
}

function of skb_put_padto
static inline int skb_put_padto(struct sk_buff *skb, unsigned int len)
{
	return __skb_put_padto(skb, len, true);
}

function of __skb_put_padto
static inline int __skb_put_padto(struct sk_buff *skb, unsigned int len,
				  bool free_on_error)
{
	unsigned int size = skb->len;

	if (unlikely(size < len)) {
		len -= size;
		if (__skb_pad(skb, len, free_on_error))
			return -ENOMEM;
		__skb_put(skb, len);
	}
	return 0;
}

Signed-off-by: Carl Huang <cjhuang@...eaurora.org>
Signed-off-by: Wen Gong <wgong@...eaurora.org>
Cc: Doug Anderson <dianders@...omium.org>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/qrtr/qrtr.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/qrtr/qrtr.c
+++ b/net/qrtr/qrtr.c
@@ -203,7 +203,7 @@ static int qrtr_node_enqueue(struct qrtr
 	hdr->size = cpu_to_le32(len);
 	hdr->confirm_rx = 0;

-	skb_put_padto(skb, ALIGN(len, 4));
+	skb_put_padto(skb, ALIGN(len, 4) + sizeof(*hdr));

 	mutex_lock(&node->ep_lock);
 	if (node->ep)