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bpf: Add bpf_prog_run_data_pointers()

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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 ec624fe740 ("net/sched:
Extend qdisc control block with tc control block"), which added a wrong
interaction with db58ba4592 ("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: ec624fe740 ("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
This commit is contained in:
Eric Dumazet
2025-11-12 12:55:16 +00:00
committed by Martin KaFai Lau
parent 91a78ce994
commit 4ef9274362
3 changed files with 24 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
include/linux/filter.h
View File

@@ -901,6 +901,26 @@ 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.
*/

6
net/sched/act_bpf.c
View File

@@ -47,12 +47,10 @@ TC_INDIRECT_SCOPE int tcf_bpf_act(struct sk_buff *skb,
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->tstamp_type))
skb->tstamp_type = SKB_CLOCK_REALTIME;

6
net/sched/cls_bpf.c
View File

@@ -97,12 +97,10 @@ TC_INDIRECT_SCOPE int cls_bpf_classify(struct sk_buff *skb,
} 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->tstamp_type))
skb->tstamp_type = SKB_CLOCK_REALTIME;