netdev - [PATCH net 2/2] net/sched: cls_u32: use skb_header_pointer

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Message-ID: <20260127144433.196836-3-edumazet@google.com>
Date: Tue, 27 Jan 2026 14:44:33 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Jamal Hadi Salim <jhs@...atatu.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, 
	GangMin Kim <km.kim1503@...il.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net 2/2] net/sched: cls_u32: use skb_header_pointer_careful()

skb_header_pointer() does not fully validate negative @offset values.

Use skb_header_pointer_careful() instead.

GangMin Kim provided a report and a repro fooling u32_classify():

BUG: KASAN: slab-out-of-bounds in u32_classify+0x1180/0x11b0
net/sched/cls_u32.c:221

Many many thanks to GangMin!

Fixes: fbc2e7d9cf49 ("cls_u32: use skb_header_pointer() to dereference data safely")
Reported-by: GangMin Kim <km.kim1503@...il.com>
Closes: https://lore.kernel.org/netdev/CANn89iJkyUZ=mAzLzC4GdcAgLuPnUoivdLaOs6B9rq5_erj76w@mail.gmail.com/T/
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/sched/cls_u32.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 2a1c00048fd6f4b700bee11c80502aa3ff993331..58e849c0acf412d3a5ed5cd9a2b32929a720cb17 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -161,10 +161,8 @@ TC_INDIRECT_SCOPE int u32_classify(struct sk_buff *skb,
 			int toff = off + key->off + (off2 & key->offmask);
 			__be32 *data, hdata;
 
-			if (skb_headroom(skb) + toff > INT_MAX)
-				goto out;
-
-			data = skb_header_pointer(skb, toff, 4, &hdata);
+			data = skb_header_pointer_careful(skb, toff, 4,
+							  &hdata);
 			if (!data)
 				goto out;
 			if ((*data ^ key->val) & key->mask) {
@@ -214,8 +212,9 @@ TC_INDIRECT_SCOPE int u32_classify(struct sk_buff *skb,
 		if (ht->divisor) {
 			__be32 *data, hdata;
 
-			data = skb_header_pointer(skb, off + n->sel.hoff, 4,
-						  &hdata);
+			data = skb_header_pointer_careful(skb,
+							  off + n->sel.hoff,
+							  4, &hdata);
 			if (!data)
 				goto out;
 			sel = ht->divisor & u32_hash_fold(*data, &n->sel,
@@ -229,7 +228,7 @@ TC_INDIRECT_SCOPE int u32_classify(struct sk_buff *skb,
 			if (n->sel.flags & TC_U32_VAROFFSET) {
 				__be16 *data, hdata;
 
-				data = skb_header_pointer(skb,
+				data = skb_header_pointer_careful(skb,
 							  off + n->sel.offoff,
 							  2, &hdata);
 				if (!data)
-- 
2.53.0.rc1.217.geba53bf80e-goog