[PATCH 9/9] net, ipv4: convert fib_info.fib_clntref from atomic_t to refcount_t

[Elena Reshetova]

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshet...@intel.com>
Signed-off-by: Hans Liljestrand <ishkam...@gmail.com>
Signed-off-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: David Windsor <dwind...@gmail.com>
---
 include/net/ip_fib.h     | 7 ++++---
 net/ipv4/fib_semantics.c | 2 +-
 net/ipv4/fib_trie.c      | 2 +-
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 368bb40..55d2694 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -23,6 +23,7 @@
 #include <net/inetpeer.h>
 #include <linux/percpu.h>
 #include <linux/notifier.h>
+#include <linux/refcount.h>
 
 struct fib_config {
        u8                      fc_dst_len;
@@ -105,7 +106,7 @@ struct fib_info {
        struct hlist_node       fib_lhash;
        struct net              *fib_net;
        int                     fib_treeref;
-       atomic_t                fib_clntref;
+       refcount_t              fib_clntref;
        unsigned int            fib_flags;
        unsigned char           fib_dead;
        unsigned char           fib_protocol;
@@ -407,12 +408,12 @@ void free_fib_info(struct fib_info *fi);
 
 static inline void fib_info_hold(struct fib_info *fi)
 {
-       atomic_inc(&fi->fib_clntref);
+       refcount_inc(&fi->fib_clntref);
 }
 
 static inline void fib_info_put(struct fib_info *fi)
 {
-       if (atomic_dec_and_test(&fi->fib_clntref))
+       if (refcount_dec_and_test(&fi->fib_clntref))
                free_fib_info(fi);
 }
 
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 317026a..9c361bd 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1174,7 +1174,7 @@ struct fib_info *fib_create_info(struct fib_config *cfg)
        }
 
        fi->fib_treeref++;
-       atomic_inc(&fi->fib_clntref);
+       refcount_set(&fi->fib_clntref, 1);
        spin_lock_bh(&fib_info_lock);
        hlist_add_head(&fi->fib_hash,
                       &fib_info_hash[fib_info_hashfn(fi)]);
diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 2f0d823..d3bbe6e 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -1543,7 +1543,7 @@ int fib_table_lookup(struct fib_table *tb, const struct 
flowi4 *flp,
                        }
 
                        if (!(fib_flags & FIB_LOOKUP_NOREF))
-                               atomic_inc(&fi->fib_clntref);
+                               refcount_inc(&fi->fib_clntref);
 
                        res->prefixlen = KEYLENGTH - fa->fa_slen;
                        res->nh_sel = nhsel;
-- 
2.7.4