[PATCH 6.6 107/166] net: sched: fix TCF_LAYER_TRANSPORT handling in tcf_get_base_ptr()

Greg Kroah-Hartman
2026-04-24T13:38:05Z

From: Eric Dumazet <edumazet@google.com>

[Upstream commit 4fe5a00ec70717a7f1002d8913ec6143582b3c8e]

syzbot reported that tcf_get_base_ptr() can be called while transport
header is not set [1].

Instead of returning a dangling pointer, return NULL.

Fix tcf_get_base_ptr() callers to handle this NULL value.

[1]
WARNING: CPU: 1 PID: 6019 at ./include/linux/skbuff.h:3071 skb_transport_header include/linux/skbuff.h:3071 [inline]
WARNING: CPU: 1 PID: 6019 at ./include/linux/skbuff.h:3071 tcf_get_base_ptr include/net/pkt_cls.h:539 [inline]
WARNING: CPU: 1 PID: 6019 at ./include/linux/skbuff.h:3071 em_nbyte_match+0x2d8/0x3f0 net/sched/em_nbyte.c:43
Modules linked in:
CPU: 1 UID: 0 PID: 6019 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Call Trace:
<TASK>
tcf_em_match net/sched/ematch.c:494 [inline]
__tcf_em_tree_match+0x1ac/0x770 net/sched/ematch.c:520
tcf_em_tree_match include/net/pkt_cls.h:512 [inline]
basic_classify+0x115/0x2d0 net/sched/cls_basic.c:50
tc_classify include/net/tc_wrapper.h:197 [inline]
__tcf_classify net/sched/cls_api.c:1764 [inline]
tcf_classify+0x4cf/0x1140 net/sched/cls_api.c:1860
multiq_classify net/sched/sch_multiq.c:39 [inline]
multiq_enqueue+0xfd/0x4c0 net/sched/sch_multiq.c:66
dev_qdisc_enqueue+0x4e/0x260 net/core/dev.c:4118
__dev_xmit_skb net/core/dev.c:4214 [inline]
__dev_queue_xmit+0xe83/0x3b50 net/core/dev.c:4729
packet_snd net/packet/af_packet.c:3076 [inline]
packet_sendmsg+0x3e33/0x5080 net/packet/af_packet.c:3108
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg+0x21c/0x270 net/socket.c:742
____sys_sendmsg+0x505/0x830 net/socket.c:2630

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+f3a497f02c389d86ef16@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6920855a.a70a0220.2ea503.0058.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20251121154100.1616228-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Chelsy Ratnawat <chelsyratnawat2001@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/pkt_cls.h | 2 ++
net/sched/em_cmp.c | 5 ++++-
net/sched/em_nbyte.c | 2 ++
net/sched/em_text.c | 11 +++++++++--
4 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index f308e8268651e..ccc1c698ed007 100644
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -525,6 +525,8 @@ static inline unsigned char * tcf_get_base_ptr(struct sk_buff *skb, int layer)
case TCF_LAYER_NETWORK:
return skb_network_header(skb);
case TCF_LAYER_TRANSPORT:
+ if (!skb_transport_header_was_set(skb))
+ break;
return skb_transport_header(skb);
}

diff --git a/net/sched/em_cmp.c b/net/sched/em_cmp.c
index f17b049ea5309..71ce113f2d08e 100644
--- a/net/sched/em_cmp.c
+++ b/net/sched/em_cmp.c
@@ -22,9 +22,12 @@ static int em_cmp_match(struct sk_buff *skb, struct tcf_ematch *em,
struct tcf_pkt_info *info)
{
struct tcf_em_cmp *cmp = (struct tcf_em_cmp *) em->data;
- unsigned char *ptr = tcf_get_base_ptr(skb, cmp->layer) + cmp->off;
+ unsigned char *ptr = tcf_get_base_ptr(skb, cmp->layer);
u32 val = 0;

+ if (!ptr)
+ return 0;
+ ptr += cmp->off;
if (!tcf_valid_offset(skb, ptr, cmp->align))
return 0;

diff --git a/net/sched/em_nbyte.c b/net/sched/em_nbyte.c
index a83b237cbeb06..2e3c1d58d4563 100644
--- a/net/sched/em_nbyte.c
+++ b/net/sched/em_nbyte.c
@@ -42,6 +42,8 @@ static int em_nbyte_match(struct sk_buff *skb, struct tcf_ematch *em,
struct nbyte_data *nbyte = (struct nbyte_data *) em->data;
unsigned char *ptr = tcf_get_base_ptr(skb, nbyte->hdr.layer);

+ if (!ptr)
+ return 0;
ptr += nbyte->hdr.off;

if (!tcf_valid_offset(skb, ptr, nbyte->hdr.len))
diff --git a/net/sched/em_text.c b/net/sched/em_text.c
index f176afb70559e..32aae8a9dedaa 100644
--- a/net/sched/em_text.c
+++ b/net/sched/em_text.c
@@ -29,12 +29,19 @@ static int em_text_match(struct sk_buff *skb, struct tcf_ematch *m,
struct tcf_pkt_info *info)
{
struct text_match *tm = EM_TEXT_PRIV(m);
+ unsigned char *ptr;
int from, to;

- from = tcf_get_base_ptr(skb, tm->from_layer) - skb->data;
+ ptr = tcf_get_base_ptr(skb, tm->from_layer);
+ if (!ptr)
+ return 0;
+ from = ptr - skb->data;
from += tm->from_offset;

- to = tcf_get_base_ptr(skb, tm->to_layer) - skb->data;
+ ptr = tcf_get_base_ptr(skb, tm->to_layer);
+ if (!ptr)
+ return 0;
+ to = ptr - skb->data;
to += tm->to_offset;

return skb_find_text(skb, from, to, tm->config) != UINT_MAX;
--
2.53.0