6.1-stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
[ Upstream commit 4ef92743625818932b9c320152b58274c05e5053 ]
syzbot found that cls_bpf_classify() is able to change tc_skb_cb(skb)->drop_reason triggering a warning in sk_skb_reason_drop().
WARNING: CPU: 0 PID: 5965 at net/core/skbuff.c:1192 __sk_skb_reason_drop net/core/skbuff.c:1189 [inline] WARNING: CPU: 0 PID: 5965 at net/core/skbuff.c:1192 sk_skb_reason_drop+0x76/0x170 net/core/skbuff.c:1214
struct tc_skb_cb has been added in commit ec624fe740b4 ("net/sched: Extend qdisc control block with tc control block"), which added a wrong interaction with db58ba459202 ("bpf: wire in data and data_end for cls_act_bpf").
drop_reason was added later.
Add bpf_prog_run_data_pointers() helper to save/restore the net_sched storage colliding with BPF data_meta/data_end.
Fixes: ec624fe740b4 ("net/sched: Extend qdisc control block with tc control block") Reported-by: syzbot syzkaller@googlegroups.com Closes: https://lore.kernel.org/netdev/6913437c.a70a0220.22f260.013b.GAE@google.com/ Signed-off-by: Eric Dumazet edumazet@google.com Signed-off-by: Martin KaFai Lau martin.lau@kernel.org Reviewed-by: Victor Nogueira victor@mojatatu.com Acked-by: Jamal Hadi Salim jhs@mojatatu.com Link: https://patch.msgid.link/20251112125516.1563021-1-edumazet@google.com Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/filter.h | 20 ++++++++++++++++++++ net/sched/act_bpf.c | 6 ++---- net/sched/cls_bpf.c | 6 ++---- 3 files changed, 24 insertions(+), 8 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h index bbdae97d50c42..502cab01e9e97 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -676,6 +676,26 @@ static inline void bpf_compute_data_pointers(struct sk_buff *skb) cb->data_end = skb->data + skb_headlen(skb); }
+static inline int bpf_prog_run_data_pointers( + const struct bpf_prog *prog, + struct sk_buff *skb) +{ + struct bpf_skb_data_end *cb = (struct bpf_skb_data_end *)skb->cb; + void *save_data_meta, *save_data_end; + int res; + + save_data_meta = cb->data_meta; + save_data_end = cb->data_end; + + bpf_compute_data_pointers(skb); + res = bpf_prog_run(prog, skb); + + cb->data_meta = save_data_meta; + cb->data_end = save_data_end; + + return res; +} + /* Similar to bpf_compute_data_pointers(), except that save orginal * data in cb->data and cb->meta_data for restore. */ diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c index b79eee44e24eb..e33a6be877def 100644 --- a/net/sched/act_bpf.c +++ b/net/sched/act_bpf.c @@ -45,12 +45,10 @@ static int tcf_bpf_act(struct sk_buff *skb, const struct tc_action *act, filter = rcu_dereference(prog->filter); if (at_ingress) { __skb_push(skb, skb->mac_len); - bpf_compute_data_pointers(skb); - filter_res = bpf_prog_run(filter, skb); + filter_res = bpf_prog_run_data_pointers(filter, skb); __skb_pull(skb, skb->mac_len); } else { - bpf_compute_data_pointers(skb); - filter_res = bpf_prog_run(filter, skb); + filter_res = bpf_prog_run_data_pointers(filter, skb); } if (unlikely(!skb->tstamp && skb->mono_delivery_time)) skb->mono_delivery_time = 0; diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c index 0320e11eb248b..5820ee95fa36e 100644 --- a/net/sched/cls_bpf.c +++ b/net/sched/cls_bpf.c @@ -95,12 +95,10 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp, } else if (at_ingress) { /* It is safe to push/pull even if skb_shared() */ __skb_push(skb, skb->mac_len); - bpf_compute_data_pointers(skb); - filter_res = bpf_prog_run(prog->filter, skb); + filter_res = bpf_prog_run_data_pointers(prog->filter, skb); __skb_pull(skb, skb->mac_len); } else { - bpf_compute_data_pointers(skb); - filter_res = bpf_prog_run(prog->filter, skb); + filter_res = bpf_prog_run_data_pointers(prog->filter, skb); } if (unlikely(!skb->tstamp && skb->mono_delivery_time)) skb->mono_delivery_time = 0;