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Message-ID: <CAM0EoMmof-15_1car5Taws79h=v7jyOtDWtPxTwMp1590iXrYw@mail.gmail.com>
Date: Fri, 21 Nov 2025 12:07:51 -0500
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
eric.dumazet@...il.com, syzbot+f3a497f02c389d86ef16@...kaller.appspotmail.com
Subject: Re: [PATCH net-next] net: sched: fix TCF_LAYER_TRANSPORT handling in tcf_get_base_ptr()
On Fri, Nov 21, 2025 at 10:41 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> 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@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/6920855a.a70a0220.2ea503.0058.GAE@google.com/T/#u
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reviewed-by: Jamal Hadi Salim <jhs@...atatu.com>
cheers,
jamal
> ---
> 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 c64fd896b1f985c5f6a5b50cbb42ded640d0c9fe..99ac747b7906074c43b3eb8e34cf6c07235cc81d 100644
> --- a/include/net/pkt_cls.h
> +++ b/include/net/pkt_cls.h
> @@ -536,6 +536,8 @@ 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 64b637f18bc7d40509bf5c9f7679cfbc2922af1c..48c1bce74f498d0b4ee3d1efde96459b0dac5896 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 4f9f21a05d5e40aadfdc4c339b8178ad43dc2c8b..c65ffa5fff946edbc30a65ad99087bf664665e32 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 6b3d0af72c39c7fb1e3290e24bf94f5bf9e0b358..692e2be1793e9961bcd4516baf54a05341f6ac5d 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;
> --
> 2.52.0.460.gd25c4c69ec-goog
>
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