[PATCH net-next 0/4] ynl/ethtool/netlink: warn nla_len overflow for large string sets

[Hangbin Liu <liuhangbin@gmail.com>]

This series addresses a silent data corruption issue triggered when ynl
retrieves string sets from NICs with a large number of statistics entries
(e.g. mlx5_core with thousands of ETH_SS_STATS strings).

The root cause is that struct nlattr.nla_len is a __u16 (max 65535
bytes). When a NIC exports enough statistics strings, the
ETHTOOL_A_STRINGSET_STRINGS nest built by strset_fill_set() exceeds
this limit. nla_nest_end() silently truncates the length on assignment,
producing a corrupted netlink message. In the doit path the corrupted
message is delivered to userspace without any error; in the dumpit path
an -EMSGSIZE may be returned if the data does not fit in the dump skb.

Patch 1 improves the userspace tool: rename the doit/dumpit helpers
to do_set/do_get and convert do_get to use ynl.do() with an
explicit device header instead of a full dump with client-side filtering.

Patch 2 adds a --dbg-small-recv option to the YNL ethtool tool,
matching the same option already present in cli.py, to aid debugging
of netlink message size issues.

Patch 3 is the kernel fix: check whether the strings_attr nest would
exceed U16_MAX before calling nla_nest_end() in strset_fill_set(),
and return -EMSGSIZE early if so.

Patch 4 adds a generic WARN_ON_ONCE() in nla_nest_end() itself, so
that any future caller hitting the same overflow is immediately visible
in the kernel log rather than silently corrupting data.

---
Hangbin Liu (4):
      tools: ynl: ethtool: use doit instead of dumpit for per-device GET
      tools: ynl: ethtool: add --dbg-small-recv option
      ethtool: strset: check nla_len overflow before nla_nest_end
      netlink: warn on nla_len overflow in nla_nest_end()

 include/net/netlink.h          |  1 +
 net/ethtool/strset.c           |  4 +++
 tools/net/ynl/pyynl/ethtool.py | 77 ++++++++++++++++++++++--------------------
 3 files changed, 46 insertions(+), 36 deletions(-)
---
base-commit: dc9e9d61e301c087bcd990dbf2fa18ad3e2e1429
change-id: 20260324-b4-ynl_ethtool-f87cd42f572c

Best regards,
-- 
Hangbin Liu <liuhangbin@gmail.com>