netdev - [PATCH net] net: ethtool: fix off-by-one error in max RSS context IDs

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Message-ID: <20240806160126.551306-1-edward.cree@amd.com>
Date: Tue, 6 Aug 2024 17:01:26 +0100
From: <edward.cree@....com>
To: <davem@...emloft.net>, <kuba@...nel.org>, <edumazet@...gle.com>,
	<pabeni@...hat.com>
CC: Edward Cree <ecree.xilinx@...il.com>, <netdev@...r.kernel.org>
Subject: [PATCH net] net: ethtool: fix off-by-one error in max RSS context IDs

From: Edward Cree <ecree.xilinx@...il.com>

Both ethtool_ops.rxfh_max_context_id and the default value used when
 it's not specified are supposed to be exclusive maxima (the former
 is documented as such; the latter, U32_MAX, cannot be used as an ID
 since it equals ETH_RXFH_CONTEXT_ALLOC), but xa_alloc() expects an
 inclusive maximum.
Subtract one from 'limit' to produce an inclusive maximum, and pass
 that to xa_alloc().  Special-case limit==0 to avoid overflow.

Fixes: 6603754cd914 ("net: ethtool: let the core choose RSS context IDs")
Signed-off-by: Edward Cree <ecree.xilinx@...il.com>
---
 net/ethtool/ioctl.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index 8ca13208d240..de34ea9b9665 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -1453,8 +1453,13 @@ static noinline_for_stack int ethtool_set_rxfh(struct net_device *dev,
 			u32 ctx_id;
 
 			/* driver uses new API, core allocates ID */
-			ret = xa_alloc(&dev->ethtool->rss_ctx, &ctx_id, ctx,
-				       XA_LIMIT(1, limit), GFP_KERNEL_ACCOUNT);
+			if (limit)
+				ret = xa_alloc(&dev->ethtool->rss_ctx, &ctx_id,
+					       ctx, XA_LIMIT(1, limit - 1),
+					       GFP_KERNEL_ACCOUNT);
+			else
+				/* match xa_alloc's 'no free entries' result */
+				ret = -EBUSY;
 			if (ret < 0) {
 				kfree(ctx);
 				goto out;