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Wed, 07 Oct 2026 10:36:13 -0700 (PDT) From: Josef Bacik Date: Wed, 07 Oct 2026 17:36:00 +0000 Subject: [PATCH net-next v2 1/8] 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 Message-Id: <20261007-b4-skbuff-bug-on-v2-1-b9a5f732895b@toxicpanda.com> References: <20261007-b4-skbuff-bug-on-v2-0-b9a5f732895b@toxicpanda.com> In-Reply-To: <20261007-b4-skbuff-bug-on-v2-0-b9a5f732895b@toxicpanda.com> To: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Josef Bacik X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=openssh-sha256; t=1791394570; l=1395; i=josef@toxicpanda.com; h=from:subject:message-id; bh=j/d4+6UO1zMm/OSkoPxAoOFd0Pid5fsU1BUtdsYxUhA=; b=U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgUBr36M/n0nWN0DNbnxwzIiCZez6MG JiruuNaSCI/zXsAAAAGcGF0YXR0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5AAAA QMuGVBMQK42cE/Snfa08JC0fmwBrbf2GQNY3ya6ddo+CZ+JOvEDsXz/NSgzmaXVXIxa3Y07tuSV +hFZ2GlKKiwE= X-Developer-Key: i=josef@toxicpanda.com; a=openssh; fpr=SHA256:C8kOX2QUJCMqnCX+KEeoqRAjLo9L+ELOSH2NSAJHqGA 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. Return -EINVAL instead of crashing. The warning is DEBUG_NET_WARN_ON_ONCE(), so debug kernels still point at the caller, while production kernels, including ones running with panic_on_warn, just fail the call. Assisted-by: LLM Signed-off-by: Josef Bacik --- net/core/skbuff.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 43ebe61c7fc4..d226fe77d484 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -2303,9 +2303,15 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, u8 *data; int i; - BUG_ON(nhead < 0); + if (unlikely(nhead < 0)) { + DEBUG_NET_WARN_ON_ONCE(1); + return -EINVAL; + } - BUG_ON(skb_shared(skb)); + if (unlikely(skb_shared(skb))) { + DEBUG_NET_WARN_ON_ONCE(1); + return -EINVAL; + } skb_zcopy_downgrade_managed(skb); -- 2.55.0