Re: [syzbot] [batman?] KMSAN: uninit-value in skb_clone

[shaurya]

#syz test:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
From 55661c87a847ed20bafa072ea6ba90e345fcfb58 Mon Sep 17 00:00:00 2001
From: Shaurya Rane <ssrane_b23@xxxxxxxxxxxxx>
Date: Sat, 29 Nov 2025 21:29:17 +0530
Subject: [PATCH net v3] net: hsr: fix NULL pointer dereference in
 prp_get_untagged_frame()

__pskb_copy() can return NULL if memory allocation fails. When this
happens in prp_get_untagged_frame(), frame->skb_std remains NULL and
is passed to skb_clone(), causing a NULL pointer dereference.

Add a NULL check immediately after __pskb_copy() to return early
when allocation fails.

 BUG: KMSAN: uninit-value in skb_clone+0x1e0/0x420 net/core/skbuff.c:2129
  skb_clone+0x1e0/0x420 net/core/skbuff.c:2129
  prp_get_untagged_frame net/hsr/hsr_forward.c:217 [inline]
  hsr_forward_do+0x2fe0/0x59d0 net/hsr/hsr_forward.c:663
  hsr_forward_skb+0x330/0x460 net/hsr/hsr_forward.c:720
  hsr_dev_xmit+0x4a/0x80 net/hsr/hsr_device.c:199

Reported-by: syzbot+e2ca1ef26dc1c7387658@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug\?extid\=e2ca1ef26dc1c7387658
Fixes: 451d8123f897 ("net: prp: add packet handling support")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Shaurya Rane <ssrane_b23@xxxxxxxxxxxxx>
---
 net/hsr/hsr_forward.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
index 339f0d220212..aefc9b6936ba 100644
--- a/net/hsr/hsr_forward.c
+++ b/net/hsr/hsr_forward.c
@@ -205,6 +205,8 @@ struct sk_buff *prp_get_untagged_frame(struct hsr_frame_info *frame,
 				__pskb_copy(frame->skb_prp,
 					    skb_headroom(frame->skb_prp),
 					    GFP_ATOMIC);
+			if (!frame->skb_std)
+				return NULL;
 		} else {
 			/* Unexpected */
 			WARN_ONCE(1, "%s:%d: Unexpected frame received (port_src %s)\n",
-- 
2.34.1