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

[Ido Schimmel <idosch@nvidia.com>]

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/
> 
> Cc: Yuwei Wang <wangyuweihx@gmail.com>
> ---
>  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