2021-03-28 08:15:30

by Lv Yunlong

Subject: [PATCH] drivers/net/wan/hdlc_fr: Fix a double free in pvc_xmit

In pvc_xmit, if __skb_pad(skb, pad, false) failed, it will free
the skb in the first time and goto drop. But the same skb is freed
by kfree_skb(skb) in the second time in drop.

Maintaining the original function unchanged, my patch adds a new
label out to avoid the double free if __skb_pad() failed.

Fixes: f5083d0cee08a ("drivers/net/wan/hdlc_fr: Improvements to the code of pvc_xmit")
Signed-off-by: Lv Yunlong <[email protected]>
---
drivers/net/wan/hdlc_fr.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
index 0720f5f92caa..4d9dc7d15908 100644
--- a/drivers/net/wan/hdlc_fr.c
+++ b/drivers/net/wan/hdlc_fr.c
@@ -415,7 +415,7 @@ static netdev_tx_t pvc_xmit(struct sk_buff *skb, struct net_device *dev)

if (pad > 0) { /* Pad the frame with zeros */
if (__skb_pad(skb, pad, false))
- goto drop;
+ goto out;
skb_put(skb, pad);
}
}
@@ -448,8 +448,9 @@ static netdev_tx_t pvc_xmit(struct sk_buff *skb, struct net_device *dev)
return NETDEV_TX_OK;

drop:
- dev->stats.tx_dropped++;
kfree_skb(skb);
+out:
+ dev->stats.tx_dropped++;
return NETDEV_TX_OK;
}

--
2.25.1

2021-03-29 01:21:57

by patchwork-bot+netdevbpf

Subject: Re: [PATCH] drivers/net/wan/hdlc_fr: Fix a double free in pvc_xmit

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Sun, 28 Mar 2021 00:50:08 -0700 you wrote:
> In pvc_xmit, if __skb_pad(skb, pad, false) failed, it will free
> the skb in the first time and goto drop. But the same skb is freed
> by kfree_skb(skb) in the second time in drop.
>
> Maintaining the original function unchanged, my patch adds a new
> label out to avoid the double free if __skb_pad() failed.
>
> [...]

Here is the summary with links:
- drivers/net/wan/hdlc_fr: Fix a double free in pvc_xmit
https://git.kernel.org/netdev/net/c/1b479fb80160

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

2021-05-03 06:09:21

by Xie He

Subject: Re: [PATCH] drivers/net/wan/hdlc_fr: Fix a double free in pvc_xmit

> In pvc_xmit, if __skb_pad(skb, pad, false) failed, it will free
> the skb in the first time and goto drop. But the same skb is freed
> by kfree_skb(skb) in the second time in drop.
>
> Maintaining the original function unchanged, my patch adds a new
> label out to avoid the double free if __skb_pad() failed.
>
> Fixes: f5083d0cee08a ("drivers/net/wan/hdlc_fr: Improvements to the code of pvc_xmit")
> Signed-off-by: Lv Yunlong <[email protected]>
> ---
> drivers/net/wan/hdlc_fr.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
> index 0720f5f92caa..4d9dc7d15908 100644
> --- a/drivers/net/wan/hdlc_fr.c
> +++ b/drivers/net/wan/hdlc_fr.c
> @@ -415,7 +415,7 @@ static netdev_tx_t pvc_xmit(struct sk_buff *skb, struct net_device *dev)
>
> if (pad > 0) { /* Pad the frame with zeros */
> if (__skb_pad(skb, pad, false))
> - goto drop;
> + goto out;
> skb_put(skb, pad);
> }
> }
> @@ -448,8 +448,9 @@ static netdev_tx_t pvc_xmit(struct sk_buff *skb, struct net_device *dev)
> return NETDEV_TX_OK;
>
> drop:
> - dev->stats.tx_dropped++;
> kfree_skb(skb);
> +out:
> + dev->stats.tx_dropped++;
> return NETDEV_TX_OK;
> }
>

1. This patch is incorrect. "__skb_pad" will NOT free the skb on failure
when its "free_on_error" parameter is "false".

2. If you think you fix my commit, please CC me so that I can review
your patch.

I have sent another patch to revert this.