From 9e741045faea17e28663f14a45f7f3304827c968 Mon Sep 17 00:00:00 2001 From: Vivien Didelot Date: Fri, 24 Nov 2017 11:36:06 -0500 Subject: [PATCH] net: dsa: fix 'increment on 0' warning Setting the refcount to 0 when allocating a tree to match the number of switch devices it holds may cause an 'increment on 0; use-after-free', if CONFIG_REFCOUNT_FULL is enabled. To fix this, do not decrement the refcount of a newly allocated tree, increment it when an already allocated tree is found, and decrement it after the probing of a switch, as done with the previous behavior. At the same time, make dsa_tree_get and dsa_tree_put accept a NULL argument to simplify callers, and return the tree after incrementation, as most kref users like of_node_get and of_node_put do. Fixes: 8e5bf9759a06 ("net: dsa: simplify tree reference counting") Signed-off-by: Vivien Didelot Reviewed-by: Florian Fainelli Tested-by: Florian Fainelli Signed-off-by: David S. Miller --- net/dsa/dsa2.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c index 44e3fb7dec8c..1e287420ff49 100644 --- a/net/dsa/dsa2.c +++ b/net/dsa/dsa2.c @@ -51,9 +51,7 @@ static struct dsa_switch_tree *dsa_tree_alloc(int index) INIT_LIST_HEAD(&dst->list); list_add_tail(&dsa_tree_list, &dst->list); - /* Initialize the reference counter to the number of switches, not 1 */ kref_init(&dst->refcount); - refcount_set(&dst->refcount.refcount, 0); return dst; } @@ -64,20 +62,23 @@ static void dsa_tree_free(struct dsa_switch_tree *dst) kfree(dst); } -static struct dsa_switch_tree *dsa_tree_touch(int index) +static struct dsa_switch_tree *dsa_tree_get(struct dsa_switch_tree *dst) { - struct dsa_switch_tree *dst; - - dst = dsa_tree_find(index); - if (!dst) - dst = dsa_tree_alloc(index); + if (dst) + kref_get(&dst->refcount); return dst; } -static void dsa_tree_get(struct dsa_switch_tree *dst) +static struct dsa_switch_tree *dsa_tree_touch(int index) { - kref_get(&dst->refcount); + struct dsa_switch_tree *dst; + + dst = dsa_tree_find(index); + if (dst) + return dsa_tree_get(dst); + else + return dsa_tree_alloc(index); } static void dsa_tree_release(struct kref *ref) @@ -91,7 +92,8 @@ static void dsa_tree_release(struct kref *ref) static void dsa_tree_put(struct dsa_switch_tree *dst) { - kref_put(&dst->refcount, dsa_tree_release); + if (dst) + kref_put(&dst->refcount, dsa_tree_release); } static bool dsa_port_is_dsa(struct dsa_port *port) @@ -765,6 +767,7 @@ int dsa_register_switch(struct dsa_switch *ds) mutex_lock(&dsa2_mutex); err = dsa_switch_probe(ds); + dsa_tree_put(ds->dst); mutex_unlock(&dsa2_mutex); return err; -- 2.30.2