Re: [PATCH ovpn net v4 5/9] ovpn: zero-initialize sockaddr before learning a floated endpoint

2026-07-28, 13:48:51 +0200, Antonio Quartulli wrote:
> From: Antonio Quartulli <[email protected]>
> 
> ovpn_peer_endpoints_update() builds the new remote endpoint in an
> on-stack struct sockaddr_storage that is left uninitialized. For IPv4
> only sin_family/sin_addr/sin_port are written, leaving the 8-byte
> sin_zero padding as stack garbage (for IPv6, sin6_flowinfo is left
> uninitialized likewise).
> 
> ovpn_peer_reset_sockaddr() -> ovpn_bind_from_sockaddr() then memcpy()s
> sizeof(struct sockaddr_in)/sizeof(struct sockaddr_in6) bytes - padding
> included - into bind->remote. That buffer is later hashed with jhash()
> over the same length to place the peer in the by_transp_addr table, so
> the garbage padding lands the floated peer in an essentially random
> bucket. Lockless lookups in ovpn_peer_get_by_transp_addr() build their
> key from a zero-initialized sockaddr_storage, compute a different bucket
> and fail to find the peer.
> 
> This is also a plain use of uninitialized stack memory in jhash().
> 
> Build the floated endpoint with a designated initializer so the
> padding (sin_zero for IPv4, sin6_flowinfo for IPv6) is zeroed as part
> of the assignment. This keeps the padding out of the by_transp_addr
> hash key without memset-ing the whole sockaddr_storage on every
> received packet.
> 
> Fixes: f0281c1d3732 ("ovpn: add support for updating local or remote UDP endpoint")
> Signed-off-by: Antonio Quartulli <[email protected]>
> ---
>  drivers/net/ovpn/peer.c | 31 +++++++++++++++++++++++--------
>  1 file changed, 23 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/ovpn/peer.c b/drivers/net/ovpn/peer.c
> index 3554da01e406..00971bbd3dcf 100644
> --- a/drivers/net/ovpn/peer.c
> +++ b/drivers/net/ovpn/peer.c
> @@ -244,9 +244,16 @@ void ovpn_peer_endpoints_update(struct ovpn_peer *peer, struct sk_buff *skb)
>  			 */
>  			local_ip = &ip_hdr(skb)->daddr;
>  			sa = (struct sockaddr_in *)&ss;
> -			sa->sin_family = AF_INET;
> -			sa->sin_addr.s_addr = ip_hdr(skb)->saddr;
> -			sa->sin_port = udp_hdr(skb)->source;
> +			/* use a designated initializer so the sin_zero padding
> +			 * is zeroed (it ends up in the by_transp_addr hash key)
> +			 * without memset-ing the whole sockaddr_storage on the
> +			 * RX fast path
> +			 */
> +			*sa = (struct sockaddr_in) {
> +				.sin_family = AF_INET,
> +				.sin_addr.s_addr = ip_hdr(skb)->saddr,
> +				.sin_port = udp_hdr(skb)->source,
> +			};

I'm running behind on reviews, so I missed this version of the patch
until it landed on netdev. I find this syntax really ugly. I get that
sashiko was upset about the useless memset [*], but a memset in that
branch would have been fine too.

[*] sometimes it's also ok to ignore it. a small memset, even in the
hotpath, probably has a non-measurable effect on throughput for a
codepath that also encrypts/decrypts full packets.

-- 
Sabrina