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Fri, 17 Apr 2026 21:57:18 -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, horms@kernel.org, andrew+netdev@lunn.ch Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, Jason Xing Subject: [PATCH net 2/4] xsk: free the skb when hitting the upper bound MAX_SKB_FRAGS Date: Sat, 18 Apr 2026 12:56:42 +0800 Message-Id: <20260418045644.28612-3-kerneljasonxing@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20260418045644.28612-1-kerneljasonxing@gmail.com> References: <20260418045644.28612-1-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 Fix it by explicitly adding kfree_skb() before returning back to its caller. How to reproduce it in virtio_net: 1. the current skb is the first one (which means xs->skb is NULL) and hit the limit MAX_SKB_FRAGS. 2. xsk_build_skb_zerocopy() returns -EOVERFLOW. 3. the caller xsk_build_skb() clears skb by using 'skb = NULL;'. This is why bug can be triggered. 4. there is no chance to free this skb anymore. Note that if in this case the xs->skb is not NULL, xsk_build_skb() will call xsk_drop_skb(xs->skb) to do the right thing. Fixes: cf24f5a5feea ("xsk: add support for AF_XDP multi-buffer on Tx path") Signed-off-by: Jason Xing --- net/xdp/xsk.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index 8fcde34aec7b..5d3dbb118730 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -778,8 +778,11 @@ static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs, addr = buffer - pool->addrs; for (copied = 0, i = skb_shinfo(skb)->nr_frags; copied < len; i++) { - if (unlikely(i >= MAX_SKB_FRAGS)) + if (unlikely(i >= MAX_SKB_FRAGS)) { + if (!xs->skb) + kfree_skb(skb); return ERR_PTR(-EOVERFLOW); + } page = pool->umem->pgs[addr >> PAGE_SHIFT]; get_page(page); -- 2.41.3