From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yx1-f50.google.com (mail-yx1-f50.google.com [74.125.224.50]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ABF2A4AA594 for ; Wed, 7 Oct 2026 14:51:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.224.50 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791384672; cv=none; b=bWRHw89h1jo7LFHMAmhJbi3wo7RyFJruej0000IWlnvah/8Amr4JzyZwEiCIIDrcz5FR67o0idcl00o1esFHaz1QIo7fTrWYH9e1fP0/qCC6L9VLL1IB4xuA3kKODigVYqQJEF1xqln35PN5rWUmXXy8BzwZkoCUGmyiC5j+fps= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791384672; c=relaxed/simple; bh=zg/uWw1C9tuSxeBV3eFBhNDtdmOBp+EfUsAftSVbJTc=; h=Date:From:To:Cc:Message-ID:In-Reply-To:References:Subject: MIME-Version:Content-Type; b=En4kGsHV8igXUdWs1BkMLmxjml84dBQqw9/hOgdid44/1DImx1CgwhDui7YlyXBAKeo4hrOgRlGxjtJbYbLSst30TtcCu/SVETWnigcOYSBDnrGuSsf3QyyFxuPFmjH8ACfs9aO+zuqzB9LhsKMvqv1J4wn5O7oIhvUFRbX0Zpk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=c61zuYBY; arc=none smtp.client-ip=74.125.224.50 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="c61zuYBY" Received: by mail-yx1-f50.google.com with SMTP id 956f58d0204a3-677c1fc082bso3558531d50.3 for ; Wed, 07 Oct 2026 07:51:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1791384667; x=1791989467; darn=vger.kernel.org; h=content-transfer-encoding:content-type:mime-version:subject :references:in-reply-to:message-id:cc:to:from:date:from:to:cc :subject:date:message-id:reply-to:content-type; bh=YACwyXnL3UskMX5dK960KQ1iZfinHNnmBFhBCvvDh5k=; b=c61zuYBYytyJwqC2tJKeP6CGunPFCSNS5tS/mzIXaXxDHHi5/vQ9ceqV/PSyxVYZwI Wks4N4Pt5n/kv2/Xhbg7Bdqedo+3vITLvw+1wwnM/mKFKc774lPO7rg6SMEmbQrnrXQa GLEo+4AAy9AbGgnAtK8FdZy9NBJD7Xog/zqZCN2hDXdMmjJ/mcA1D8d/ZMW0zK3msV+7 f9zMHJDp9C2m8Jng6c2DHfWj9BoeAV3QJX9C9xLjZwUQLAixt/7YTld5bP4u0q5tPfgr btMR/En/i/NnvvyyCV39B3FCi3GEUKe4nK+XT+YC90xvLPdgb4XH+Q5xZac6ZvCwvqjK KNnw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1791384667; x=1791989467; h=content-transfer-encoding:content-type:mime-version:subject :references:in-reply-to:message-id:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=YACwyXnL3UskMX5dK960KQ1iZfinHNnmBFhBCvvDh5k=; b=KhSt07BTHWdXhpwnh9I/KwWVKWTf0zx4glpEdbZ/PmFXrlp0SoRf9D1LJUrdSVlwxP Tga992nWfJrfMtTYSGGoSzi9+Du5VvGxznVtKHXzs9zG5zjk4SmSIqt2cCA3LYdlMZEn dkyvM8IYedc6rAlBlOkhgBhzXS5BrTdA38rWQi0vykbDgBPplhalz/+R8h9jMsub6dfl Is3r8G43Goi4CY0zB/+2wMKjmng5uR6YCZtu96iP6OST0joZIVuMhLeB+Q8MZ8DdDw/E d4yOzyBkCMQT9NaGzvtO0fpBJ9vkNnTJCY5K1tsjolDNpUGV2ecXAULK/PCalJ1mkblV G5UQ== X-Forwarded-Encrypted: i=1; AKwUvBxxF4tix8qlZCWzINi7qheu6XfZ6QTlYlbld4rGquirkYVrEnGVp3SLftTfWWO8MTT0Ib+4B+A8I1U3TC4=@vger.kernel.org X-Gm-Message-State: AFq9FYLRq1/fUtAD+PrqD/IMKApTbachOS188bGgmmMfaqdVu5K2hEDE 4XMh9ifIWRH9AzVg5jPy+zoLa+X2/rxvElz6m0/X/fnkPVD9dQV6g9Pr X-Gm-Gg: AYBFou02yv9Zhw+9TAH9d6hXmS19F90wvmgB80E6bBhFSmHZ3X2fmNiGb0WCrgepk9i l/88HxPRmzIiUQoaTv5kAYDEV/XpDjF0HfvoK3XNoPXEVUTxpHCtXC8uJ55w4hCtLdATyMDXD91 yDNBa47towClVyMnRf6avQXxVB9dUXCW6idYIsxxUbaioehXHwRa5vN19K19q8wvmFE3IWpvw1h Q+Iio8sMgTf+N9MvAv1JE+aVNYjC9mJazd9H7xcktakph4kCiD87+7IvV1tEV/GBAssMpt6nVh8 0fdlPw//5jL1ry4P2TzK28qPqNlp+TbSA5X/K17NCt/xkpDK6cyJmOQ/4zYyTEpnmNmTTMWliwm 1LQChtVEfQnoR8yVtxq1jtBcFoIMieBaTE80WyR4w98vvtKZAYg6EgPlOUDYu3Si+bVAV0jhp6w oPdJkR5adNDxtJuGNClBLr8ZCDki2tF58pYUJ+T6XrzGMKDKnEMPmKAV0wHDtWdYuQ0QcYOW3zO RlG5GmTDr65GiYLtruY09siHGVEN7MfcAZig33EfA/HFG1tEacuHgyfvf5DAv2++cY/jBdu9ur8 j9IvOlv2He0qk7LG4bgivyw8MdiDQ/S+pkJknREj3UPlcl5T X-Received: by 2002:a05:690e:4893:20b0:66e:5e37:2ff2 with SMTP id 956f58d0204a3-6790a0d5b89mr877402d50.4.1791384667246; Wed, 07 Oct 2026 07:51:07 -0700 (PDT) Received: from gmail.com (111.46.245.35.bc.googleusercontent.com. [35.245.46.111]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-6791afa71ddsm163923d50.4.2026.10.07.07.51.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Oct 2026 07:51:05 -0700 (PDT) Date: Wed, 07 Oct 2026 10:51:05 -0400 From: Willem de Bruijn To: Josef Bacik , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Kaiyuan Zhang , Mina Almasry , Willem de Bruijn Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Josef Bacik Message-ID: In-Reply-To: <20261006-b4-skbuff-bug-on-v1-2-1b4434c5357c@toxicpanda.com> References: <20261006-b4-skbuff-bug-on-v1-0-1b4434c5357c@toxicpanda.com> <20261006-b4-skbuff-bug-on-v1-2-1b4434c5357c@toxicpanda.com> Subject: Re: [PATCH net-next 2/9] net: skbuff: don't BUG() on bad arguments to pskb_expand_head() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Josef Bacik wrote: > pskb_expand_head() BUG()s if it is handed a negative nhead or a shared > skb. Both are bugs in the caller, and both keep getting hit: commit > 2cbb259ec4f8 ("bpf: Reject negative head_room in __bpf_skb_change_head") > and commit 64e6a754d33d ("llc: do not use skb_get() before > dev_queue_xmit()") each fixed a crash here that took down the whole box. > > The function already returns an error that every caller has to handle, > and at this point it hasn't touched the skb. Warn once and return > -EINVAL instead of crashing. Anybody running with panic_on_warn, which > includes syzbot, still stops right here. > > Assisted-by: LLM > Signed-off-by: Josef Bacik > --- > net/core/skbuff.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 512ff9cfa269..5d856948cef9 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -2303,9 +2303,11 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, > u8 *data; > int i; > > - BUG_ON(nhead < 0); > + if (WARN_ON_ONCE(nhead < 0)) > + return -EINVAL; Another option besides WARN_ON_ONCE or even DEBUG_NET_WARN_ON_ONCE when returning an error is a net_warn_ratelimited for such cases. > > - BUG_ON(skb_shared(skb)); > + if (WARN_ON_ONCE(skb_shared(skb))) > + return -EINVAL; > > skb_zcopy_downgrade_managed(skb); > > > -- > 2.55.0 >