On 5/21/26 3:33 PM, Kees Cook wrote:

Add a new struct kernel_param_ops::get callback whose signature
takes a struct seq_buf instead of a raw char buffer:

  int (*get)(struct seq_buf *sb, const struct kernel_param *kp);

The previously-legacy .get field is now .get_str (char *buffer);
.get is the new seq_buf-aware form.  param_attr_show() prefers .get
when set, otherwise falls back to .get_str.  WARN_ON_ONCE() if both
are set.  Return contract for .get:

  < 0 : errno propagated to userspace; seq_buf contents discarded
  = 0 : success; length derived from seq_buf_used()
  > 0 : forbidden; the dispatcher WARN_ON_ONCE()s and treats as 0

The default policy on seq_buf_has_overflowed() is silent truncation,
matching scnprintf()/sysfs_emit() behaviour.  Callbacks that want a
specific overflow errno can check seq_buf_has_overflowed() and
return their preferred error.

No callbacks use .get yet; the legacy path is still the only one in use
after this commit. A subsequent commit teaches DEFINE_KERNEL_PARAM_OPS
to route initializers by type.

Signed-off-by: Kees Cook <kees@kernel.org>

Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>

-- Petr