| Message ID | 1417706452-30204-1-git-send-email-linux@rasmusvillemoes.dk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, 4 Dec 2014 16:20:52 +0100 Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote: > 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. > > Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> > --- > > Notes: > How this could ever have worked is beyond me - compare_blob seems to > be used to maintain an rbtree, and I wouldn't expect rbtrees to behave > well if the comparison function doesn't satisfy the basic invariant > sign(cmp(a, b)) == -sign(cmp(b, a)). > > fs/nfsd/nfs4state.c | 15 +++++++-------- > 1 file changed, 7 insertions(+), 8 deletions(-) > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > index e9c3afe4b5d3..d504cd6927f8 100644 > --- a/fs/nfsd/nfs4state.c > +++ b/fs/nfsd/nfs4state.c > @@ -1711,15 +1711,14 @@ static int copy_cred(struct svc_cred *target, struct svc_cred *source) > 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 *new_clp, struct rb_root *root) > 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; > Ouch! Well spotted. I'd have probably stuck with just casting the lengths to long longs, but this is not a particularly hot codepath and so I'm ok with this. This should probably also go to stable. Reviewed-by: Jeff Layton <jlayton@primarydata.com> -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index e9c3afe4b5d3..d504cd6927f8 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -1711,15 +1711,14 @@ static int copy_cred(struct svc_cred *target, struct svc_cred *source) 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 *new_clp, struct rb_root *root) 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;
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. Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> --- Notes: How this could ever have worked is beyond me - compare_blob seems to be used to maintain an rbtree, and I wouldn't expect rbtrees to behave well if the comparison function doesn't satisfy the basic invariant sign(cmp(a, b)) == -sign(cmp(b, a)). fs/nfsd/nfs4state.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)