From 3dec153ae484e3b2ddac841156e197ba54c8df94 Mon Sep 17 00:00:00 2001 From: Jason Xing Date: Sat, 2 May 2026 23:07:19 +0300 Subject: xsk: prevent CQ desync when freeing half-built skbs in xsk_build_skb() 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. Postpone the init phase when we believe the allocation of first frag is successfully completed. Before this init, skb can be safely freed by kfree_skb(). Closes: https://lore.kernel.org/all/20260419045822.843BFC2BCAF@smtp.kernel.org/ Fixes: c30d084960cf ("xsk: avoid overwriting skb fields for multi-buffer traffic") Acked-by: Stanislav Fomichev Signed-off-by: Jason Xing Reviewed-by: Alexander Lobakin Link: https://patch.msgid.link/20260502200722.53960-6-kerneljasonxing@gmail.com Signed-off-by: Jakub Kicinski --- net/xdp/xsk.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index 55378c3855d5..af3c5752bb63 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -819,8 +819,6 @@ static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs, return ERR_PTR(err); skb_reserve(skb, hr); - - xsk_skb_init_misc(skb, xs, desc->addr); if (desc->options & XDP_TX_METADATA) { err = xsk_skb_metadata(skb, buffer, desc, pool, hr); if (unlikely(err)) @@ -917,7 +915,6 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs, if (unlikely(err)) goto free_err; - xsk_skb_init_misc(skb, xs, desc->addr); if (desc->options & XDP_TX_METADATA) { err = xsk_skb_metadata(skb, buffer, desc, xs->pool, hr); @@ -967,6 +964,8 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs, } } + if (!xs->skb) + xsk_skb_init_misc(skb, xs, desc->addr); xsk_inc_num_desc(skb); return skb; -- cgit v1.2.3