[PATCH 3.14 50/77] fs: nfsd: Fix signedness bug in compare_blob

Greg Kroah-Hartman
2015-01-14T07:58:54Z

From: Rasmus Villemoes <linux@rasmusvillemoes.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@primarydata.com>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1209,15 +1209,14 @@ 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)
@@ -1401,7 +1400,7 @@ 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;