Re: [PATCH v1 net 2/4] neighbour: Enforce min/max to NDTPA_INTERVAL_PROBE_TIME_MS.

On Mon, Sep 07, 2026 at 09:57:53PM +0000, Kuniyuki Iwashima wrote:

NDTPA_INTERVAL_PROBE_TIME_MS sets .type and .min but misses
.validation_type, so no validation is applied:

  # ynl --family rt-neigh --do setneightbl \
  --json '{"name": "arp_cache", "parms": {"interval-probe-time-ms": 0}}'

  # ynl --family rt-neigh --dump getneightbl --output-json | \
  jq '.[] | select(.name == "arp_cache" and has("config"))
          | .parms["interval-probe-time-ms"]'
  0

Moreover, nla_get_msecs() uses msecs_to_jiffies(), and u64 is
silently cast to u32, so a larger value can bypass the min check:

  e.g. 4294967296 == 0x100000000

  # ynl --family rt-neigh --do setneightbl \
  --json '{"name": "arp_cache", "parms": {"interval-probe-time-ms": 4294967296}}'

  # ynl --family rt-neigh --dump getneightbl --output-json | \
  jq '.[] | select(.name == "arp_cache" and has("config"))
          | .parms["interval-probe-time-ms"]'
  0

msecs_to_jiffies() returns MAX_JIFFY_OFFSET if the value is
larger than INT_MAX.  Also, INT_MAX ms overflows int NEIGH_VAR()
when HZ > 1000 (Alpha, MIPS), and passing a negative integer to
queue_delayed_work(unsigned long delay) causes sign extension,
which wraps around the expiry time to the past, resulting in it
being handled as 0 delay in the timer wheel.

Let's use NLA_POLICY_FULL_RANGE() and limit the max to 1 day.

Please add a note that this controls the probe interval for "managed"
entries and therefore a max of 1 day is unlikely to break any
deployments.

The same max check is applied to sysctl as well.

Fixes: 211da42eaa45 ("net, neigh: introduce interval_probe_time_ms for periodic probe")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
Currently, the sysctl range check is not applied to
interval_probe_time_ms, which needs this fix:
https://lore.kernel.org/linux-fsdevel/20260905233819.1064529-2-kuniyu@google.com/ (local)

Cc: Yuwei Wang <redacted>
---
 net/core/neighbour.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

The maximum value should be documented in Documentation/networking/ip-sysctl.rst

Also in Documentation/netlink/specs/rt-neigh.yaml:

diff --git a/Documentation/netlink/specs/rt-neigh.yaml b/Documentation/netlink/specs/rt-neigh.yaml
index 0f46ef313590..c8e55c98d564 100644
--- a/Documentation/netlink/specs/rt-neigh.yaml
+++ b/Documentation/netlink/specs/rt-neigh.yaml

@@ -341,6 +341,9 @@ attribute-sets:
       -
         name: interval-probe-time-ms
         type: u64
+        checks:
+          min: 1
+          max: 86400000
 
 operations:
   enum-model: directional