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[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: bpf@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 >