linux-kernel - [PATCH] hsr: fix NULL pointer dereference in skb

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Message-Id: <20251125210158.224431-1-ssranevjti@gmail.com>
Date: Wed, 26 Nov 2025 02:31:58 +0530
From: ssrane_b23@...vjti.ac.in
To: "David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>,
	Felix Maurer <fmaurer@...hat.com>,
	Jaakko Karrenpalo <jkarrenpalo@...il.com>,
	Arvid Brodin <arvid.brodin@...en.se>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev,
	david.hunter.linux@...il.com,
	khalid@...nel.org,
	Shaurya Rane <ssrane_b23@...vjti.ac.in>,
	syzbot+2fa344348a579b779e05@...kaller.appspotmail.com
Subject: [PATCH] hsr: fix NULL pointer dereference in skb_clone with hw tag insertion

From: Shaurya Rane <ssrane_b23@...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@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=2fa344348a579b779e05
Fixes: f266a683a480 ("net/hsr: Better frame dispatch")
Signed-off-by: Shaurya Rane <ssrane_b23@...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