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Mon, 20 Apr 2026 08:44:04 -0700 (PDT) Date: Mon, 20 Apr 2026 08:44:04 -0700 From: Stanislav Fomichev To: Jason Xing Cc: 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, bpf@vger.kernel.org, netdev@vger.kernel.org, Jason Xing Subject: Re: [PATCH net 2/4] xsk: free the skb when hitting the upper bound MAX_SKB_FRAGS Message-ID: References: <20260418045644.28612-1-kerneljasonxing@gmail.com> <20260418045644.28612-3-kerneljasonxing@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260418045644.28612-3-kerneljasonxing@gmail.com> On 04/18, Jason Xing wrote: > 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 > As mentioned for patch 1, need to do something with that xsk_skb_init_misc... Otherwise we hit destructor with xsk_cq_submit_addr_locked here as well