[PATCH v2] net/sched: act_skbedit: fix divide-by-zero in tcf_skbedit_hash()

[Ruitong Liu <cnitlrt@gmail.com>]

Commit 38a6f0865796 ("net: sched: support hash selecting tx queue")
added SKBEDIT_F_TXQ_SKBHASH support. mapping_mod is computed as:

  mapping_mod = queue_mapping_max - queue_mapping + 1;

mapping_mod is stored as u16, so the calculation can overflow when the
requested range covers 65536 queues (e.g. queue_mapping=0 and
queue_mapping_max=0xffff). In that case mapping_mod wraps to 0 and
tcf_skbedit_hash() triggers a divide-by-zero:

  queue_mapping += skb_get_hash(skb) % params->mapping_mod;

Reject such invalid configuration to prevent mapping_mod from becoming
0 and avoid the crash.

Fixes: 38a6f0865796 ("net: sched: support hash selecting tx queue")
Cc: stable@vger.kernel.org # 6.12+
Reported-by: Ruitong Liu <cnitlrt@gmail.com>
Reported-by: Shuyuan Liu <L0x1c3r@gmail.com>
Signed-off-by: Ruitong Liu <cnitlrt@gmail.com>
---
 net/sched/act_skbedit.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sched/act_skbedit.c b/net/sched/act_skbedit.c
index 8c1d1554f657..b6f5c21651fc 100644
--- a/net/sched/act_skbedit.c
+++ b/net/sched/act_skbedit.c
@@ -194,6 +194,10 @@ static int tcf_skbedit_init(struct net *net, struct nlattr *nla,
 			}
 
 			mapping_mod = *queue_mapping_max - *queue_mapping + 1;
+			if (!mapping_mod) {
+				NL_SET_ERR_MSG_MOD(extack, "Invalid queue_mapping range: range too large");
+				return -EINVAL;
+			}
 			flags |= SKBEDIT_F_TXQ_SKBHASH;
 		}
 		if (*pure_flags & SKBEDIT_F_INHERITDSFIELD)
-- 
2.34.1