bnxt: fix crashes when reducing ring count with active RSS contexts

bnxt doesn't check if a ring is used by RSS contexts when reducing
ring count. Core performs a similar check for the drivers for
the main context, but core doesn't know about additional contexts,
so it can't validate them. bnxt_fill_hw_rss_tbl_p5() uses ring
id to index bp->rx_ring[], which without the check may end up
being out of bounds.

  BUG: KASAN: slab-out-of-bounds in __bnxt_hwrm_vnic_set_rss+0xb79/0xe40
  Read of size 2 at addr ffff8881c5809618 by task ethtool/31525
  Call Trace:
  __bnxt_hwrm_vnic_set_rss+0xb79/0xe40
   bnxt_hwrm_vnic_rss_cfg_p5+0xf7/0x460
   __bnxt_setup_vnic_p5+0x12e/0x270
   __bnxt_open_nic+0x2262/0x2f30
   bnxt_open_nic+0x5d/0xf0
   ethnl_set_channels+0x5d4/0xb30
   ethnl_default_set_doit+0x2f1/0x620

Core does track the additional contexts in net-next, so we can
move this validation out of the driver as a follow up there.

Fixes: b3d0083 ("bnxt_en: Support RSS contexts in ethtool .{get|set}_rxfh()")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Link: https://patch.msgid.link/20240705020005.681746-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: kuba-moo

drivers/net/ethernet/broadcom/bnxt/bnxt.c

@@ -6146,6 +6146,21 @@ static u16 bnxt_get_max_rss_ring(struct bnxt *bp)
 	return max_ring;
 }
 
+u16 bnxt_get_max_rss_ctx_ring(struct bnxt *bp)
+{
+	u16 i, tbl_size, max_ring = 0;
+	struct bnxt_rss_ctx *rss_ctx;
+
+	tbl_size = bnxt_get_rxfh_indir_size(bp->dev);
+
+	list_for_each_entry(rss_ctx, &bp->rss_ctx_list, list) {
+		for (i = 0; i < tbl_size; i++)
+			max_ring = max(max_ring, rss_ctx->rss_indir_tbl[i]);
+	}
+
+	return max_ring;
+}
+
 int bnxt_get_nr_rss_ctxs(struct bnxt *bp, int rx_rings)
 {
 	if (bp->flags & BNXT_FLAG_CHIP_P5_PLUS) {

drivers/net/ethernet/broadcom/bnxt/bnxt.h

@@ -2776,6 +2776,7 @@ int bnxt_hwrm_vnic_set_tpa(struct bnxt *bp, struct bnxt_vnic_info *vnic,
 void bnxt_fill_ipv6_mask(__be32 mask[4]);
 int bnxt_alloc_rss_indir_tbl(struct bnxt *bp, struct bnxt_rss_ctx *rss_ctx);
 void bnxt_set_dflt_rss_indir_tbl(struct bnxt *bp, struct bnxt_rss_ctx *rss_ctx);
+u16 bnxt_get_max_rss_ctx_ring(struct bnxt *bp);
 int bnxt_get_nr_rss_ctxs(struct bnxt *bp, int rx_rings);
 int bnxt_hwrm_vnic_cfg(struct bnxt *bp, struct bnxt_vnic_info *vnic);
 int bnxt_hwrm_vnic_alloc(struct bnxt *bp, struct bnxt_vnic_info *vnic,

drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c

@@ -961,6 +961,12 @@ static int bnxt_set_channels(struct net_device *dev,
 		return rc;
 	}
 
+	if (req_rx_rings < bp->rx_nr_rings &&
+	    req_rx_rings <= bnxt_get_max_rss_ctx_ring(bp)) {
+		netdev_warn(dev, "Can't deactivate rings used by RSS contexts\n");
+		return -EINVAL;
+	}
+
 	if (bnxt_get_nr_rss_ctxs(bp, req_rx_rings) !=
 	    bnxt_get_nr_rss_ctxs(bp, bp->rx_nr_rings) &&
 	    netif_is_rxfh_configured(dev)) {