[PATCH net v2 2/3] net/sched: cls_bpf: accept dev-bound programs on shared blocks

[Jamal Hadi Salim <jhs@mojatatu.com>]

The issue:
Follow-up to commit 120977e2c096 ("net/sched: cls_bpf: reject dev-bound
programs bound to a different device"), which derived the target device
from block->q:

	dev = block->q ? qdisc_dev(block->q) : NULL;

tcf_block_create() leaves block->q NULL for shared blocks, so a
device-bound program attached through a shared block is rejected with
-EINVAL even when it is bound to a netdev that owns the block.  The
offload path (cls_bpf_offload_cmd()) never consults block->q and drives
the per-device callbacks for shared blocks as before.

The Fix:
Accept the attach on a shared block when bpf_offload_dev_match() matches
every netdev bound to the block, and reject an empty block.  Every member
must match because the offload path broadcasts the program to every
callback registered on the block, so an any-member check would re-admit
the wrong-device attach on a mixed block.  Every dev-bound SCHED_CLS
attach is skip_sw, which becomes err_stop and aborts the offload on the
first failing callback, so the all-members rule is the offload path's own
semantics.

Iterate the public block->ports xarray (913b47d3424e, v6.8-rc1) rather
than block->owner_list, which is private to cls_api.c.  The shared-block
rejection reports "Program is not bound to every device in the block",
distinct from the non-shared message, because a member can exist without
a registered callback (netdevsim registers its block callback
ingress-only).

Context note:
This patch is not an independent fix: it re-exposes the shared-block
replay path that commit 120977e2c096 ("net/sched: cls_bpf: reject
dev-bound programs bound to a different device") had closed, so patch 1
must be applied first, including in stable.  A stable tree taking this
patch alone would re-enable shared-block attaches on a kernel whose
netdevsim callback is still unchecked.

Conditions to recreate the bug:
  - CONFIG_NETDEVSIM=y, CONFIG_NET_CLS_BPF=y
  - load a dev-bound SCHED_CLS program for netdevsim device B
    (prog_ifindex=B), pin it in bpffs
  - tc qdisc add dev B ingress_block 22 clsact
  - tc filter add block 22 ingress bpf da object-pinned <pin> skip_sw
  Unfixed, the filter add fails with -EINVAL ("Program is bound to a
  different device"); fixed, it succeeds.  Adding a second, independently
  backed netdevsim device to the same block makes the attach fail again.

Fixes: 120977e2c096 ("net/sched: cls_bpf: reject dev-bound programs bound to a different device")
Reported-by: Sashiko (nipa) <sashiko-bot@kernel.org>
Link: https://lore.kernel.org/netdev/20260809094418.901607-1-jhs@mojatatu.com/
Link: https://lore.kernel.org/netdev/QDISC-PYC7.v1.20261003103747@mojatatu.com/
Cc: stable@vger.kernel.org
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
v1 -> v2 (v2 of an on-list patch; v1 posted 2026-10-04):

- Finding (nipa Sashiko High, v1) -- FIXED: the
  every-member predicate is enforced only at add/replace, but a netdev
  joining a shared block later is replayed the stored filter by
  cls_bpf_reoffload() before it is inserted into block->ports
  (tcf_block_offload_bind precedes the xa_insert).  Neither
  cls_bpf_reoffload() nor nsim_bpf_setup_tc_block_cb() checked
  bpf_offload_dev_match(), so the B-bound program was installed on the
  joining device (re-opening the 120977e2c096 mixed-block defect).
  Fixed by enforcing the device match in nsim_bpf_setup_tc_block_cb()
  (drivers/net/netdevsim/bpf.c), mirroring nfp.
- Style (gemini + nipa Low) -- FIXED: the shared-block comment opens with
  /* on its own line.
- The companion selftest exercises shared-block and late-join coverage,
  pinning both the all-members predicate and this callback's replay gate.
- Split the single v2 draft into [PATCH net v2 1/3] netdevsim,
  2/3 cls_bpf and 3/3 selftests, each with its own Fixes: and stable
  metadata.
---
 net/sched/cls_bpf.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
index 188cf0f949dd..bbd2dc2f518f 100644
--- a/net/sched/cls_bpf.c
+++ b/net/sched/cls_bpf.c
@@ -392,11 +392,31 @@ static int cls_bpf_prog_from_efd(struct nlattr **tb, struct cls_bpf_prog *prog,
 	if (bpf_prog_is_dev_bound(fp->aux)) {
 		struct tcf_block *block = tp->chain->block;
 		struct net_device *dev;
+		unsigned long ifindex;
+		bool match = false;
+
+		/* A shared block has no qdisc of its own, but it may bind
+		 * several netdevs and the program is offloaded to all of them;
+		 * require a match with every member.
+		 */
+		if (!tcf_block_shared(block)) {
+			dev = qdisc_dev(tcf_block_q(block));
+			match = bpf_offload_dev_match(fp, dev);
+			if (!match)
+				NL_SET_ERR_MSG(extack,
+					       "Program is bound to a different device");
+		} else {
+			xa_for_each(&block->ports, ifindex, dev) {
+				match = bpf_offload_dev_match(fp, dev);
+				if (!match)
+					break;
+			}
+			if (!match)
+				NL_SET_ERR_MSG(extack,
+					       "Program is not bound to every device in the block");
+		}
 
-		dev = block->q ? qdisc_dev(block->q) : NULL;
-		if (!dev || !bpf_offload_dev_match(fp, dev)) {
-			NL_SET_ERR_MSG(extack,
-				       "Program is bound to a different device");
+		if (!match) {
 			bpf_prog_put(fp);
 			return -EINVAL;
 		}
-- 
2.43.0