linux-kernel - [PATCH 3.18 102/150] fs: nfsd: Fix signedness bug in compare

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Message-Id: <20150114072100.485902739@linuxfoundation.org>
Date:	Tue, 13 Jan 2015 23:22:53 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Jeff Layton <jlayton@...marydata.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	"J. Bruce Fields" <bfields@...hat.com>
Subject: [PATCH 3.18 102/150] fs: nfsd: Fix signedness bug in compare_blob

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Rasmus Villemoes <linux@...musvillemoes.dk>

commit ef17af2a817db97d42dd2ec0a425231748e23dbc upstream.

Bugs similar to the one in acbbe6fbb240 (kcmp: fix standard comparison
bug) are in rich supply.

In this variant, the problem is that struct xdr_netobj::len has type
unsigned int, so the expression o1->len - o2->len _also_ has type
unsigned int; it has completely well-defined semantics, and the result
is some non-negative integer, which is always representable in a long
long. But this means that if the conditional triggers, we are
guaranteed to return a positive value from compare_blob.

In this case it could be fixed by

-       res = o1->len - o2->len;
+       res = (long long)o1->len - (long long)o2->len;

but I'd rather eliminate the usually broken 'return a - b;' idiom.

Reviewed-by: Jeff Layton <jlayton@...marydata.com>
Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/nfsd/nfs4state.c |   15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1711,15 +1711,14 @@ static int copy_cred(struct svc_cred *ta
 	return 0;
 }

-static long long
+static int
 compare_blob(const struct xdr_netobj *o1, const struct xdr_netobj *o2)
 {
-	long long res;
-
-	res = o1->len - o2->len;
-	if (res)
-		return res;
-	return (long long)memcmp(o1->data, o2->data, o1->len);
+	if (o1->len < o2->len)
+		return -1;
+	if (o1->len > o2->len)
+		return 1;
+	return memcmp(o1->data, o2->data, o1->len);
 }

 static int same_name(const char *n1, const char *n2)
@@ -1907,7 +1906,7 @@ add_clp_to_name_tree(struct nfs4_client
 static struct nfs4_client *
 find_clp_in_name_tree(struct xdr_netobj *name, struct rb_root *root)
 {
-	long long cmp;
+	int cmp;
 	struct rb_node *node = root->rb_node;
 	struct nfs4_client *clp;

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