[PATCH] hsr: fix NULL pointer dereference in skb_clone with hw tag insertion

[PATCH] hsr: fix NULL pointer dereference in skb_clone with hw tag insertion

[ssrane_b23]

From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>

When hardware HSR tag insertion is enabled (NETIF_F_HW_HSR_TAG_INS) and
frame->skb_std is NULL, both hsr_create_tagged_frame() and
prp_create_tagged_frame() will call skb_clone() with a NULL skb pointer,
causing a kernel crash.

Fix this by adding NULL checks for frame->skb_std before calling
skb_clone() in the functions.

Reported-by: syzbot+2fa344348a579b779e05@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=2fa344348a579b779e05
Fixes: f266a683a480 ("net/hsr: Better frame dispatch")
Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
---
 net/hsr/hsr_forward.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
index 339f0d220212..4c1a311b900f 100644
--- a/net/hsr/hsr_forward.c
+++ b/net/hsr/hsr_forward.c
@@ -211,6 +211,9 @@ struct sk_buff *prp_get_untagged_frame(struct hsr_frame_info *frame,
 				  __FILE__, __LINE__, port->dev->name);
 			return NULL;
 		}
+
+		if (!frame->skb_std)
+			return NULL;
 	}
 
 	return skb_clone(frame->skb_std, GFP_ATOMIC);
@@ -341,6 +344,8 @@ struct sk_buff *hsr_create_tagged_frame(struct hsr_frame_info *frame,
 		hsr_set_path_id(frame, hsr_ethhdr, port);
 		return skb_clone(frame->skb_hsr, GFP_ATOMIC);
 	} else if (port->dev->features & NETIF_F_HW_HSR_TAG_INS) {
+		if (!frame->skb_std)
+			return NULL;
 		return skb_clone(frame->skb_std, GFP_ATOMIC);
 	}
 
@@ -385,6 +390,8 @@ struct sk_buff *prp_create_tagged_frame(struct hsr_frame_info *frame,
 		}
 		return skb_clone(frame->skb_prp, GFP_ATOMIC);
 	} else if (port->dev->features & NETIF_F_HW_HSR_TAG_INS) {
+		if (!frame->skb_std)
+			return NULL;
 		return skb_clone(frame->skb_std, GFP_ATOMIC);
 	}
 
-- 
2.34.1

Re: [PATCH] hsr: fix NULL pointer dereference in skb_clone with hw tag insertion

[Simon Horman]

On Wed, Nov 26, 2025 at 02:31:58AM +0530, ssrane_b23@ee.vjti.ac.in wrote:
> From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> 
> When hardware HSR tag insertion is enabled (NETIF_F_HW_HSR_TAG_INS) and
> frame->skb_std is NULL, both hsr_create_tagged_frame() and
> prp_create_tagged_frame() will call skb_clone() with a NULL skb pointer,
> causing a kernel crash.
> 
> Fix this by adding NULL checks for frame->skb_std before calling
> skb_clone() in the functions.

I think it would be worth including the trace reported by syzcaller here.
(Say, up to but not including the "Modules linked in" line.)
I can see it at the link. But maybe the link will go away some day.

> 
> Reported-by: syzbot+2fa344348a579b779e05@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=2fa344348a579b779e05
> Fixes: f266a683a480 ("net/hsr: Better frame dispatch")
> Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>

As a fix Networking code present in the net tree, this should be
targeted at the net tree. Like this.

[PATCH net] ...

> ---
>  net/hsr/hsr_forward.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
> index 339f0d220212..4c1a311b900f 100644
> --- a/net/hsr/hsr_forward.c
> +++ b/net/hsr/hsr_forward.c
> @@ -211,6 +211,9 @@ struct sk_buff *prp_get_untagged_frame(struct hsr_frame_info *frame,
>  				  __FILE__, __LINE__, port->dev->name);
>  			return NULL;
>  		}
> +
> +		if (!frame->skb_std)
> +			return NULL;

I think this can only occur if __pskb_copy() returns NULL.
So, for clarity, I think this condition should be moved to immediately
after the call to __pskb_copy().

>  	}
>  
>  	return skb_clone(frame->skb_std, GFP_ATOMIC);

...

-- 
pw-bot: changes-requested

Re: [PATCH] hsr: fix NULL pointer dereference in skb_clone with hw tag insertion

[Greg KH]

On Wed, Nov 26, 2025 at 02:31:58AM +0530, ssrane_b23@ee.vjti.ac.in wrote:
> From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> 
> When hardware HSR tag insertion is enabled (NETIF_F_HW_HSR_TAG_INS) and
> frame->skb_std is NULL, both hsr_create_tagged_frame() and
> prp_create_tagged_frame() will call skb_clone() with a NULL skb pointer,
> causing a kernel crash.
> 
> Fix this by adding NULL checks for frame->skb_std before calling
> skb_clone() in the functions.
> 
> Reported-by: syzbot+2fa344348a579b779e05@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=2fa344348a579b779e05
> Fixes: f266a683a480 ("net/hsr: Better frame dispatch")
> Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> ---
>  net/hsr/hsr_forward.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
> index 339f0d220212..4c1a311b900f 100644
> --- a/net/hsr/hsr_forward.c
> +++ b/net/hsr/hsr_forward.c
> @@ -211,6 +211,9 @@ struct sk_buff *prp_get_untagged_frame(struct hsr_frame_info *frame,
>  				  __FILE__, __LINE__, port->dev->name);
>  			return NULL;
>  		}
> +
> +		if (!frame->skb_std)
> +			return NULL;
>  	}
>  
>  	return skb_clone(frame->skb_std, GFP_ATOMIC);
> @@ -341,6 +344,8 @@ struct sk_buff *hsr_create_tagged_frame(struct hsr_frame_info *frame,
>  		hsr_set_path_id(frame, hsr_ethhdr, port);
>  		return skb_clone(frame->skb_hsr, GFP_ATOMIC);
>  	} else if (port->dev->features & NETIF_F_HW_HSR_TAG_INS) {
> +		if (!frame->skb_std)
> +			return NULL;
>  		return skb_clone(frame->skb_std, GFP_ATOMIC);
>  	}
>  
> @@ -385,6 +390,8 @@ struct sk_buff *prp_create_tagged_frame(struct hsr_frame_info *frame,
>  		}
>  		return skb_clone(frame->skb_prp, GFP_ATOMIC);
>  	} else if (port->dev->features & NETIF_F_HW_HSR_TAG_INS) {
> +		if (!frame->skb_std)
> +			return NULL;
>  		return skb_clone(frame->skb_std, GFP_ATOMIC);
>  	}
>  
> -- 
> 2.34.1
> 
> 
Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
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  this.

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