[PATCH 6.6 61/86] net/sched: cls_u32: use skb_header_pointer_careful()

Greg Kroah-Hartman
2026-02-09T14:50:07Z

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: Sasha Levin <sashal@kernel.org>
---
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 67f27be138487..1338d9b4c03a4 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)
--
2.51.0