lib: handle failure to change ifindex

This fixes a theoretical bug that could occur when trying to change an
ifindex on an interface to that of an existing interface. We would
remove the interface from the ifindex tree, and change the ifindex, but
when we tried to reinsert the interface, the insert would fail. It was
impossible to know if this failed due to the insertion / deletion macros
capturing the result value of the underlying BSD tree macros. So we
would effectively delete the interface.

Instead of failing on insert, we just check if the prospective ifindex
already exists and return -1 if it does.

Macros have been changed to statement expressions so the result can be
checked, and bubbled up.

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>

diff --git a/lib/if.c b/lib/if.c
index d4d9c4a5a4937f4c1b3635ae32036bad34a86da9..cc964106d04c587307a249aac56724791d641c7c 100644 (file)
--- a/lib/if.c
+++ b/lib/if.c
@@ -582,23 +582,39 @@ struct interface *if_get_by_ifindex(ifindex_t ifindex, vrf_id_t vrf_id)
        return NULL;
 }
 
-void if_set_index(struct interface *ifp, ifindex_t ifindex)
+int if_set_index(struct interface *ifp, ifindex_t ifindex)
 {
        struct vrf *vrf;
 
+       if (ifp->ifindex == ifindex)
+               return 0;
+
        vrf = vrf_get(ifp->vrf_id, NULL);
        assert(vrf);
 
-       if (ifp->ifindex == ifindex)
-               return;
+       /*
+        * If there is already an interface with this ifindex, we will collide
+        * on insertion, so don't even try.
+        */
+       if (if_lookup_by_ifindex(ifindex, ifp->vrf_id))
+               return -1;
 
        if (ifp->ifindex != IFINDEX_INTERNAL)
                IFINDEX_RB_REMOVE(vrf, ifp);
 
        ifp->ifindex = ifindex;
 
-       if (ifp->ifindex != IFINDEX_INTERNAL)
-               IFINDEX_RB_INSERT(vrf, ifp)
+       if (ifp->ifindex != IFINDEX_INTERNAL) {
+               /*
+                * This should never happen, since we checked if there was
+                * already an interface with the desired ifindex at the top of
+                * the function. Nevertheless.
+                */
+               if (IFINDEX_RB_INSERT(vrf, ifp))
+                       return -1;
+       }
+
+       return 0;
 }
 
 void if_set_name(struct interface *ifp, const char *name)

diff --git a/lib/if.h b/lib/if.h
index 4ca2e795724a31bac78cc5edbe275bf459d86914..ac8d8e70ba2f024388017fab9abd2709a4d1414b 100644 (file)
--- a/lib/if.h
+++ b/lib/if.h
@@ -308,33 +308,58 @@ RB_HEAD(if_index_head, interface);
 RB_PROTOTYPE(if_index_head, interface, index_entry, if_cmp_index_func)
 DECLARE_QOBJ_TYPE(interface)
 
-#define IFNAME_RB_INSERT(vrf, ifp)                                             \
-       if (RB_INSERT(if_name_head, &vrf->ifaces_by_name, (ifp)))              \
-               flog_err(EC_LIB_INTERFACE,                                     \
-                        "%s(%s): corruption detected -- interface with this " \
-                        "name exists already in VRF %u!",                     \
-                        __func__, (ifp)->name, (ifp)->vrf_id);
-
-#define IFNAME_RB_REMOVE(vrf, ifp)                                             \
-       if (RB_REMOVE(if_name_head, &vrf->ifaces_by_name, (ifp)) == NULL)      \
-               flog_err(EC_LIB_INTERFACE,                                     \
-                        "%s(%s): corruption detected -- interface with this " \
-                        "name doesn't exist in VRF %u!",                      \
-                        __func__, (ifp)->name, (ifp)->vrf_id);
-
-#define IFINDEX_RB_INSERT(vrf, ifp)                                            \
-       if (RB_INSERT(if_index_head, &vrf->ifaces_by_index, (ifp)))            \
-               flog_err(EC_LIB_INTERFACE,                                     \
-                        "%s(%u): corruption detected -- interface with this " \
-                        "ifindex exists already in VRF %u!",                  \
-                        __func__, (ifp)->ifindex, (ifp)->vrf_id);
-
-#define IFINDEX_RB_REMOVE(vrf, ifp)                                            \
-       if (RB_REMOVE(if_index_head, &vrf->ifaces_by_index, (ifp)) == NULL)    \
-               flog_err(EC_LIB_INTERFACE,                                     \
-                        "%s(%u): corruption detected -- interface with this " \
-                        "ifindex doesn't exist in VRF %u!",                   \
-                        __func__, (ifp)->ifindex, (ifp)->vrf_id);
+#define IFNAME_RB_INSERT(vrf, ifp)                                                    \
+       ({                                                                            \
+               struct interface *_iz =                                               \
+                       RB_INSERT(if_name_head, &vrf->ifaces_by_name, (ifp));         \
+               if (_iz)                                                              \
+                       flog_err(                                                     \
+                               EC_LIB_INTERFACE,                                     \
+                               "%s(%s): corruption detected -- interface with this " \
+                               "name exists already in VRF %u!",                     \
+                               __func__, (ifp)->name, (ifp)->vrf_id);                \
+               _iz;                                                                  \
+       })
+
+#define IFNAME_RB_REMOVE(vrf, ifp)                                                    \
+       ({                                                                            \
+               struct interface *_iz =                                               \
+                       RB_REMOVE(if_name_head, &vrf->ifaces_by_name, (ifp));         \
+               if (_iz == NULL)                                                      \
+                       flog_err(                                                     \
+                               EC_LIB_INTERFACE,                                     \
+                               "%s(%s): corruption detected -- interface with this " \
+                               "name doesn't exist in VRF %u!",                      \
+                               __func__, (ifp)->name, (ifp)->vrf_id);                \
+               _iz;                                                                  \
+       })
+
+
+#define IFINDEX_RB_INSERT(vrf, ifp)                                                   \
+       ({                                                                            \
+               struct interface *_iz = RB_INSERT(                                    \
+                       if_index_head, &vrf->ifaces_by_index, (ifp));                 \
+               if (_iz)                                                              \
+                       flog_err(                                                     \
+                               EC_LIB_INTERFACE,                                     \
+                               "%s(%u): corruption detected -- interface with this " \
+                               "ifindex exists already in VRF %u!",                  \
+                               __func__, (ifp)->ifindex, (ifp)->vrf_id);             \
+               _iz;                                                                  \
+       })
+
+#define IFINDEX_RB_REMOVE(vrf, ifp)                                                   \
+       ({                                                                            \
+               struct interface *_iz = RB_REMOVE(                                    \
+                       if_index_head, &vrf->ifaces_by_index, (ifp));                 \
+               if (_iz == NULL)                                                      \
+                       flog_err(                                                     \
+                               EC_LIB_INTERFACE,                                     \
+                               "%s(%u): corruption detected -- interface with this " \
+                               "ifindex doesn't exist in VRF %u!",                   \
+                               __func__, (ifp)->ifindex, (ifp)->vrf_id);             \
+               _iz;                                                                  \
+       })
 
 #define FOR_ALL_INTERFACES(vrf, ifp)                                           \
        if (vrf)                                                               \
@@ -502,7 +527,7 @@ extern struct interface *if_get_by_name(const char *ifname, vrf_id_t vrf_id);
 extern struct interface *if_get_by_ifindex(ifindex_t ifindex, vrf_id_t vrf_id);
 
 /* Sets the index and adds to index list */
-extern void if_set_index(struct interface *ifp, ifindex_t ifindex);
+extern int if_set_index(struct interface *ifp, ifindex_t ifindex);
 /* Sets the name and adds to name list */
 extern void if_set_name(struct interface *ifp, const char *name);