[PATCH 6.1.y 2/2] net/sched: cls_u32: use skb_header_pointer_careful()

[Bin Lan <lanbincn@139.com>]

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit cabd1a976375780dabab888784e356f574bbaed8 ]

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

Fixes: fbc2e7d9cf49 ("cls_u32: use skb_header_pointer() to dereference data safely")
Reported-by: GangMin Kim <km.kim1503@gmail.com>
Closes: https://lore.kernel.org/netdev/CANn89iJkyUZ=mAzLzC4GdcAgLuPnUoivdLaOs6B9rq5_erj76w@mail.gmail.com/T/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260128141539.3404400-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Bin Lan <lanbincn@139.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 e87d79d043d5..5e85a8bf2123 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -159,10 +159,8 @@ static int u32_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 			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) {
@@ -212,8 +210,9 @@ static int u32_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 		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,
@@ -227,7 +226,7 @@ static int u32_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 			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)
-- 
2.43.0