[PATCH net v2] tap: fix incorrect variable used for USO check in set_offload()

[Rongguang Wei <clementwei90@163.com>]

From: Rongguang Wei <weirongguang@kylinos.cn>

The USO features in set_offload() incorrectly uses feature_mask and
features argument.

The USO feature was written to the local features variable instead of
feature_mask. All other offload bits (TSO, TSO_ECN) are stored in
feature_mask which becomes tap->tap_features and is used by
tap_handle_frame() for GSO segmentation. Without NETIF_F_GSO_UDP_L4
in tap->tap_features, making USO on tap effectively non-functional.

Keeping the USO handling inside the TUN_F_CSUM block avoids enabling
GRO/LRO when userspace requests USO without CSUM.

Fixes: 399e0827642f ("driver/net/tun: Added features for USO.")
Signed-off-by: Rongguang Wei <weirongguang@kylinos.cn>
Reviewed-by: Willem de Bruijn <willemb@google.com>
---
v2: Fix more incorrect variable in USO check.
    https://lore.kernel.org/netdev/20260806163949.2807698-1-kuba@kernel.org/
v1: https://lore.kernel.org/netdev/20260805072121.117472-1-clementwei90@163.com/
---
 drivers/net/tap.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 5d2d34d24ce8..d4ca2fee538b 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -883,7 +883,7 @@ static int set_offload(struct tap_queue *q, unsigned long arg)
 
 		/* TODO: for now USO4 and USO6 should work simultaneously */
 		if ((arg & (TUN_F_USO4 | TUN_F_USO6)) == (TUN_F_USO4 | TUN_F_USO6))
-			features |= NETIF_F_GSO_UDP_L4;
+			feature_mask |= NETIF_F_GSO_UDP_L4;
 	}
 
 	/* tun/tap driver inverts the usage for TSO offloads, where
@@ -894,8 +894,7 @@ static int set_offload(struct tap_queue *q, unsigned long arg)
 	 * When user space turns off TSO, we turn off GSO/LRO so that
 	 * user-space will not receive TSO frames.
 	 */
-	if (feature_mask & (NETIF_F_TSO | NETIF_F_TSO6) ||
-	    (feature_mask & (TUN_F_USO4 | TUN_F_USO6)) == (TUN_F_USO4 | TUN_F_USO6))
+	if (feature_mask & (NETIF_F_TSO | NETIF_F_TSO6 | NETIF_F_GSO_UDP_L4))
 		features |= RX_OFFLOADS;
 	else
 		features &= ~RX_OFFLOADS;
-- 
2.25.1


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