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Mon, 20 Apr 2026 01:28:34 -0700 (PDT) From: Jason Xing To: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, bjorn@kernel.org, magnus.karlsson@intel.com, maciej.fijalkowski@intel.com, jonathan.lemon@gmail.com, sdf@fomichev.me, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, Jason Xing Subject: [PATCH net v2 4/8] xsk: prevent CQ desync when freeing half-built skbs in xsk_build_skb() Date: Mon, 20 Apr 2026 16:28:01 +0800 Message-Id: <20260420082805.14844-5-kerneljasonxing@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20260420082805.14844-1-kerneljasonxing@gmail.com> References: <20260420082805.14844-1-kerneljasonxing@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jason Xing Once xsk_skb_init_misc() has been called on an skb, its destructor is set to xsk_destruct_skb(), which submits the descriptor address(es) to the completion queue and advances the CQ producer. If such an skb is subsequently freed via kfree_skb() along an error path - before the skb has ever been handed to the driver - the destructor still runs and submits a bogus, half-initialized address to the CQ. Introduce a new common helper to fix the issue. That function will be used by the subsequent patches soon. Closes: https://lore.kernel.org/all/20260419045822.843BFC2BCAF@smtp.kernel.org/ Fixes: c30d084960cf ("xsk: avoid overwriting skb fields for multi-buffer traffic") Signed-off-by: Jason Xing --- net/xdp/xsk.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index 4fdd1a45a9bd..614e7bd1252b 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -717,6 +717,12 @@ static int xsk_skb_metadata(struct sk_buff *skb, void *buffer, return 0; } +static void xsk_drop_untrans_skb(struct sk_buff *skb) +{ + skb->destructor = sock_wfree; + kfree_skb(skb); +} + static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs, struct xdp_desc *desc) { @@ -890,7 +896,7 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs, free_err: if (skb && !xs->skb && !skb_shinfo(skb)->nr_frags) - kfree_skb(skb); + xsk_drop_untrans_skb(skb); if (err == -EOVERFLOW) { if (xs->skb) { -- 2.41.3