Merge branch 'net-pull-gso-packet-headers-in-core-stack'

Eric Dumazet says:

====================
net: pull gso packet headers in core stack

Most ndo_start_xmit() methods expects headers of gso packets
to be already in skb->head.

net/core/tso.c users are particularly at risk, because tso_build_hdr()
does a memcpy(hdr, skb->data, hdr_len);

qdisc_pkt_len_segs_init() already does a dissection of gso packets.

Use pskb_may_pull() instead of skb_header_pointer() to make
sure drivers do not have to reimplement this.

First patch is a small cleanup to ease second patch review.
====================

Link: https://patch.msgid.link/20260403221540.3297753-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 49 insertions, 35 deletions

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index de61dd5dbfd9..51855de5d208 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -74,6 +74,7 @@
 	FN(UNHANDLED_PROTO)		\
 	FN(SKB_CSUM)			\
 	FN(SKB_GSO_SEG)			\
+	FN(SKB_BAD_GSO)			\
 	FN(SKB_UCOPY_FAULT)		\
 	FN(DEV_HDR)			\
 	FN(DEV_READY)			\
@@ -392,6 +393,8 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_SKB_CSUM,
 	/** @SKB_DROP_REASON_SKB_GSO_SEG: gso segmentation error */
 	SKB_DROP_REASON_SKB_GSO_SEG,
+	/** @SKB_DROP_REASON_SKB_BAD_GSO: malicious gso packet. */
+	SKB_DROP_REASON_SKB_BAD_GSO,
 	/**
 	 * @SKB_DROP_REASON_SKB_UCOPY_FAULT: failed to copy data from user space,
 	 * e.g., via zerocopy_sg_from_iter() or skb_orphan_frags_rx()
diff --git a/net/core/dev.c b/net/core/dev.c
index 4519f0e59beb..5a31f9d2128c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4101,15 +4101,16 @@ struct sk_buff *validate_xmit_skb_list(struct sk_buff *skb, struct net_device *d
 }
 EXPORT_SYMBOL_GPL(validate_xmit_skb_list);
 
-static void qdisc_pkt_len_segs_init(struct sk_buff *skb)
+static enum skb_drop_reason qdisc_pkt_len_segs_init(struct sk_buff *skb)
 {
 	struct skb_shared_info *shinfo = skb_shinfo(skb);
+	unsigned int hdr_len, tlen;
 	u16 gso_segs;
 
 	qdisc_skb_cb(skb)->pkt_len = skb->len;
 	if (!shinfo->gso_size) {
 		qdisc_skb_cb(skb)->pkt_segs = 1;
-		return;
+		return SKB_NOT_DROPPED_YET;
 	}
 
 	qdisc_skb_cb(skb)->pkt_segs = gso_segs = shinfo->gso_segs;
@@ -4117,44 +4118,49 @@ static void qdisc_pkt_len_segs_init(struct sk_buff *skb)
 	/* To get more precise estimation of bytes sent on wire,
 	 * we add to pkt_len the headers size of all segments
 	 */
-	if (skb_transport_header_was_set(skb)) {
-		unsigned int hdr_len;
-
-		/* mac layer + network layer */
-		if (!skb->encapsulation)
-			hdr_len = skb_transport_offset(skb);
-		else
-			hdr_len = skb_inner_transport_offset(skb);
 
-		/* + transport layer */
-		if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))) {
-			const struct tcphdr *th;
-			struct tcphdr _tcphdr;
+	/* mac layer + network layer */
+	if (!skb->encapsulation) {
+		if (unlikely(!skb_transport_header_was_set(skb)))
+			return SKB_NOT_DROPPED_YET;
+		hdr_len = skb_transport_offset(skb);
+	} else {
+		hdr_len = skb_inner_transport_offset(skb);
+	}
+	/* + transport layer */
+	if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))) {
+		const struct tcphdr *th;
 
-			th = skb_header_pointer(skb, hdr_len,
-						sizeof(_tcphdr), &_tcphdr);
-			if (likely(th))
-				hdr_len += __tcp_hdrlen(th);
-		} else if (shinfo->gso_type & SKB_GSO_UDP_L4) {
-			struct udphdr _udphdr;
+		if (!pskb_may_pull(skb, hdr_len + sizeof(struct tcphdr)))
+			return SKB_DROP_REASON_SKB_BAD_GSO;
 
-			if (skb_header_pointer(skb, hdr_len,
-					       sizeof(_udphdr), &_udphdr))
-				hdr_len += sizeof(struct udphdr);
-		}
+		th = (const struct tcphdr *)(skb->data + hdr_len);
+		tlen = __tcp_hdrlen(th);
+		if (tlen < sizeof(*th))
+			return SKB_DROP_REASON_SKB_BAD_GSO;
+		hdr_len += tlen;
+		if (!pskb_may_pull(skb, hdr_len))
+			return SKB_DROP_REASON_SKB_BAD_GSO;
+	} else if (shinfo->gso_type & SKB_GSO_UDP_L4) {
+		if (!pskb_may_pull(skb, hdr_len + sizeof(struct udphdr)))
+			return SKB_DROP_REASON_SKB_BAD_GSO;
+		hdr_len += sizeof(struct udphdr);
+	}
 
-		if (unlikely(shinfo->gso_type & SKB_GSO_DODGY)) {
-			int payload = skb->len - hdr_len;
+	/* prior pskb_may_pull() might have changed skb->head. */
+	shinfo = skb_shinfo(skb);
+	if (unlikely(shinfo->gso_type & SKB_GSO_DODGY)) {
+		int payload = skb->len - hdr_len;
 
-			/* Malicious packet. */
-			if (payload <= 0)
-				return;
-			gso_segs = DIV_ROUND_UP(payload, shinfo->gso_size);
-			shinfo->gso_segs = gso_segs;
-			qdisc_skb_cb(skb)->pkt_segs = gso_segs;
-		}
-		qdisc_skb_cb(skb)->pkt_len += (gso_segs - 1) * hdr_len;
+		/* Malicious packet. */
+		if (payload <= 0)
+			return SKB_DROP_REASON_SKB_BAD_GSO;
+		gso_segs = DIV_ROUND_UP(payload, shinfo->gso_size);
+		shinfo->gso_segs = gso_segs;
+		qdisc_skb_cb(skb)->pkt_segs = gso_segs;
 	}
+	qdisc_skb_cb(skb)->pkt_len += (gso_segs - 1) * hdr_len;
+	return SKB_NOT_DROPPED_YET;
 }
 
 static int dev_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *q,
@@ -4771,6 +4777,12 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
 		     (SKBTX_SCHED_TSTAMP | SKBTX_BPF)))
 		__skb_tstamp_tx(skb, NULL, NULL, skb->sk, SCM_TSTAMP_SCHED);
 
+	reason = qdisc_pkt_len_segs_init(skb);
+	if (unlikely(reason)) {
+		dev_core_stats_tx_dropped_inc(dev);
+		kfree_skb_reason(skb, reason);
+		return -EINVAL;
+	}
 	/* Disable soft irqs for various locks below. Also
 	 * stops preemption for RCU.
 	 */
@@ -4778,7 +4790,6 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
 
 	skb_update_prio(skb);
 
-	qdisc_pkt_len_segs_init(skb);
 	tcx_set_ingress(skb, false);
 #ifdef CONFIG_NET_EGRESS
 	if (static_branch_unlikely(&egress_needed_key)) {