Re: [PATCH net-next] ethtool: tsconfig: reject zero-valued tx_type and rx_filter bitsets

[Joe Damato <joe@dama.to>]

On Wed, Aug 12, 2026 at 09:22:30AM -0700, Jakub Kicinski wrote:
> The ffs()/fls() guard in ethnl_set_tsconfig() was meant to enforce
> that the user selects exactly one tx_type (and one rx_filter)
> at a time (off / none are explicit types with non-zero values).
> However, both ffs(0) and fls(0) return 0, so the guard passes
> a zero-valued bitset through.
> 
> The subsequent ffs(req_tx_type) - 1 would produce -1, if user selected
> no bit. net_hwtstamp_validate() catches the invalid -1 downstream,
> but returns a generic error (-ERANGE) without telling the user
> what went wrong. Return -EINVAL + extack instead.
> 
> Replace the ffs()/fls() comparison with a hweight32() == 1 check.
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
> CC: andrew@lunn.ch
> CC: vadim.fedorenko@linux.dev
> ---
>  net/ethtool/tsconfig.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)

Reviewed-by: Joe Damato <joe@dama.to>