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Date:   Wed, 8 Sep 2021 17:26:05 -0400
From:   Bruce Fields <bfields@fieldses.org>
To:     Chuck Lever III <chuck.lever@oracle.com>
Cc:     Jeff Layton <jlayton@kernel.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [bug report] nfsd: Protect session creation and client confirm
 using client_lock
Message-ID: <20210908212605.GF23978@fieldses.org>
References: <20210907080732.GA20341@kili>
 <deba812574c9b898f99fc08f0c3fa23e85fc36ca.camel@kernel.org>
 <622EC724-ECBF-424D-A003-46A6B8E8C215@oracle.com>
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On Tue, Sep 07, 2021 at 03:00:23PM +0000, Chuck Lever III wrote:
> We have IPV6_SCOPE_ID_LEN as a maximum size of the scope ID,
> and it's not a big value. As long as boundary checking is made
> to be sufficient, then a stack residency for the device name
> should be safe.

Something like this?  (Or are you making a patch?  I'm not even sure how
to test.)

--b.

diff --git a/net/sunrpc/addr.c b/net/sunrpc/addr.c
index 6e4dbd577a39..d435bffc6199 100644
--- a/net/sunrpc/addr.c
+++ b/net/sunrpc/addr.c
@@ -162,8 +162,10 @@ static int rpc_parse_scope_id(struct net *net, const char *buf,
 			      const size_t buflen, const char *delim,
 			      struct sockaddr_in6 *sin6)
 {
-	char *p;
+	char p[IPV6_SCOPE_ID_LEN + 1];
 	size_t len;
+	u32 scope_id = 0;
+	struct net_device *dev;
 
 	if ((buf + buflen) == delim)
 		return 1;
@@ -175,29 +177,23 @@ static int rpc_parse_scope_id(struct net *net, const char *buf,
 		return 0;
 
 	len = (buf + buflen) - delim - 1;
-	p = kmemdup_nul(delim + 1, len, GFP_KERNEL);
-	if (p) {
-		u32 scope_id = 0;
-		struct net_device *dev;
-
-		dev = dev_get_by_name(net, p);
-		if (dev != NULL) {
-			scope_id = dev->ifindex;
-			dev_put(dev);
-		} else {
-			if (kstrtou32(p, 10, &scope_id) != 0) {
-				kfree(p);
-				return 0;
-			}
-		}
-
-		kfree(p);
-
-		sin6->sin6_scope_id = scope_id;
-		return 1;
+	if (len > IPV6_SCOPE_ID_LEN)
+		return 0;
+
+	memcpy(p, delim + 1, len);
+	p[len] = 0;
+
+	dev = dev_get_by_name(net, p);
+	if (dev != NULL) {
+		scope_id = dev->ifindex;
+		dev_put(dev);
+	} else {
+		if (kstrtou32(p, 10, &scope_id) != 0)
+			return 0;
 	}
 
-	return 0;
+	sin6->sin6_scope_id = scope_id;
+	return 1;
 }
 
 static size_t rpc_pton6(struct net *net, const char *buf, const size_t buflen,