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Tue, 21 Apr 2026 20:37:07 -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 v3 2/8] xsk: handle NULL dereference of the skb without frags issue Date: Wed, 22 Apr 2026 11:36:44 +0800 Message-Id: <20260422033650.68457-3-kerneljasonxing@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20260422033650.68457-1-kerneljasonxing@gmail.com> References: <20260422033650.68457-1-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 When a first descriptor (xs->skb == NULL) triggers -EOVERFLOW in xsk_build_skb_zerocopy (e.g., MAX_SKB_FRAGS exceeded), the free_err EOVERFLOW handler unconditionally dereferences xs->skb via xsk_inc_num_desc(xs->skb) and xsk_drop_skb(xs->skb), causing a NULL pointer dereference. In this series, the skb is already freed by kfree_skb() inside xsk_build_skb_zerocopy for the first-descriptor case, so we only need to do the bookkeeping: cancel the one reserved CQ slot and account for the single invalid descriptor. Guard the existing xsk_inc_num_desc/xsk_drop_skb calls with an xs->skb check (for the continuation case), and add an else branch for the first-descriptor case that manually cancels the CQ slot and increments invalid_descs by one. Fixes: cf24f5a5feea ("xsk: add support for AF_XDP multi-buffer on Tx path") Acked-by: Stanislav Fomichev Signed-off-by: Jason Xing --- net/xdp/xsk.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index 6149f6a79897..6521604f8d42 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -893,9 +893,14 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs, kfree_skb(skb); if (err == -EOVERFLOW) { - /* Drop the packet */ - xsk_inc_num_desc(xs->skb); - xsk_drop_skb(xs->skb); + if (xs->skb) { + /* Drop the packet */ + xsk_inc_num_desc(xs->skb); + xsk_drop_skb(xs->skb); + } else { + xsk_cq_cancel_locked(xs->pool, 1); + xs->tx->invalid_descs++; + } xskq_cons_release(xs->tx); } else { /* Let application retry */ -- 2.41.3