linux-kernel - [PATCH v2] kernfs: Fix kernfs_name

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Date:	Fri,  5 Dec 2014 23:41:33 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tejun Heo <tj@...nel.org>
Cc:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] kernfs: Fix kernfs_name_compare

Returning a difference from a comparison functions is usually wrong
(see acbbe6fbb240 "kcmp: fix standard comparison bug" for the long
story). Here there is the additional twist that if the void pointers
ns and kn->ns happen to differ by a multiple of 2^32,
kernfs_name_compare returns 0, falsely reporting a match to the
caller.

Technically 'hash - kn->hash' is ok since the hashes are restricted to
31 bits, but it's better to avoid that subtlety.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---

Notes:
    v2: Also use explicit < > comparisons of the hashes.

 fs/kernfs/dir.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 1c771931bb60..bf9e2f44c3df 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -201,10 +201,14 @@ static unsigned int kernfs_name_hash(const char *name, const void *ns)
 static int kernfs_name_compare(unsigned int hash, const char *name,
 			       const void *ns, const struct kernfs_node *kn)
 {
-	if (hash != kn->hash)
-		return hash - kn->hash;
-	if (ns != kn->ns)
-		return ns - kn->ns;
+	if (hash < kn->hash)
+		return -1;
+	if (hash > kn->hash)
+		return 1;
+	if (ns < kn->ns)
+		return -1;
+	if (ns > kn->ns)
+		return 1;
 	return strcmp(name, kn->name);
 }
 
-- 
2.1.3

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