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net/sched: act_skbedit: fix divide-by-zero in tcf_skbedit_hash()

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

mapping_mod = queue_mapping_max - queue_mapping + 1;

The range size can be 65536 when the requested range covers all possible
u16 queue IDs (e.g. queue_mapping=0 and queue_mapping_max=U16_MAX).
That value cannot be represented in a u16 and previously wrapped to 0,
so tcf_skbedit_hash() could trigger a divide-by-zero:

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

Compute mapping_mod in a wider type and reject ranges larger than U16_MAX
to prevent params->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+
Signed-off-by: Ruitong Liu <cnitlrt@gmail.com>
Link: https://patch.msgid.link/20260213175948.1505257-1-cnitlrt@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

authored by

Ruitong Liu and committed by
Jakub Kicinski be054cc6 a07c33c6

+5 -1
+5 -1
net/sched/act_skbedit.c
··· 126 126 struct tcf_skbedit *d; 127 127 u32 flags = 0, *priority = NULL, *mark = NULL, *mask = NULL; 128 128 u16 *queue_mapping = NULL, *ptype = NULL; 129 - u16 mapping_mod = 1; 129 + u32 mapping_mod = 1; 130 130 bool exists = false; 131 131 int ret = 0, err; 132 132 u32 index; ··· 194 194 } 195 195 196 196 mapping_mod = *queue_mapping_max - *queue_mapping + 1; 197 + if (mapping_mod > U16_MAX) { 198 + NL_SET_ERR_MSG_MOD(extack, "The range of queue_mapping is invalid."); 199 + return -EINVAL; 200 + } 197 201 flags |= SKBEDIT_F_TXQ_SKBHASH; 198 202 } 199 203 if (*pure_flags & SKBEDIT_F_INHERITDSFIELD)