[PATCH net v3] net: xilinx: axienet: Fix IRQ coalescing packet count overflow

[Sean Anderson <sean.anderson@linux.dev>]

If coalece_count is greater than 255 it will not fit in the register and
will overflow. This can be reproduced by running

    # ethtool -C ethX rx-frames 256

which will result in a timeout of 0us instead. Fix this by checking for
invalid values and reporting an error.

Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
Fixes: 8a3b7a252dca ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver")
---

Changes in v3:
- Validate and reject instead of silently clamping

Changes in v2:
- Use FIELD_MAX to extract the max value from the mask
- Expand the commit message with an example on how to reproduce this
  issue

 drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index 0f4b02fe6f85..c2991aeccf2b 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
@@ -2056,6 +2056,12 @@ axienet_ethtools_set_coalesce(struct net_device *ndev,
 		return -EBUSY;
 	}
 
+	if (ecoalesce->rx_max_coalesced_frames > 255 ||
+	    ecoalesce->rx_max_coalesced_frames > 255) {
+		NL_SET_ERR_MSG(extack, "frames must be less than 256");
+		return -EINVAL;
+	}
+
 	if (ecoalesce->rx_max_coalesced_frames)
 		lp->coalesce_count_rx = ecoalesce->rx_max_coalesced_frames;
 	if (ecoalesce->rx_coalesce_usecs)
-- 
2.35.1.1320.gc452695387.dirty