| Message ID | 20210415033527.26877-1-zhudi21@huawei.com |
|---|---|
| State | New |
| Headers | show |
| Series | net: fix a data race when get vlan device | expand |
dependencyOn 2021/4/15 11:35, zhudi wrote: > From: Di Zhu <zhudi21@huawei.com> > > We encountered a crash: in the packet receiving process, we got an > illegal VLAN device address, but the VLAN device address saved in vmcore > is correct. After checking the code, we found a possible data > competition: > CPU 0: CPU 1: > (RCU read lock) (RTNL lock) > vlan_do_receive() register_vlan_dev() > vlan_find_dev() > > ->__vlan_group_get_device() ->vlan_group_prealloc_vid() > > In vlan_group_prealloc_vid(), We need to make sure that kzalloc is > executed before assigning a value to vlan devices array, otherwise we As my understanding, there is a dependency between calling kzalloc() and assigning the address(returned from kzalloc()) to vg->vlan_devices_arrays, CPU and compiler can see the dependency, why can't it handling the dependency before adding the smp_wmb()? See CONTROL DEPENDENCIES section in Documentation/memory-barriers.txt: However, stores are not speculated. This means that ordering -is- provided for load-store control dependencies, as in the following example: q = READ_ONCE(a); if (q) { WRITE_ONCE(b, 1); } > may get a wrong address from the hardware cache on another cpu. > > So fix it by adding memory barrier instruction to ensure the order > of memory operations. > > Signed-off-by: Di Zhu <zhudi21@huawei.com> > --- > net/8021q/vlan.c | 2 ++ > net/8021q/vlan.h | 3 +++ > 2 files changed, 5 insertions(+) > > diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c > index 8b644113715e..4f541e05cd3f 100644 > --- a/net/8021q/vlan.c > +++ b/net/8021q/vlan.c > @@ -71,6 +71,8 @@ static int vlan_group_prealloc_vid(struct vlan_group *vg, > if (array == NULL) > return -ENOBUFS; > > + smp_wmb(); > + > vg->vlan_devices_arrays[pidx][vidx] = array; > return 0; > } > diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h > index 953405362795..7408fda084d3 100644 > --- a/net/8021q/vlan.h > +++ b/net/8021q/vlan.h > @@ -57,6 +57,9 @@ static inline struct net_device *__vlan_group_get_device(struct vlan_group *vg, > > array = vg->vlan_devices_arrays[pidx] > [vlan_id / VLAN_GROUP_ARRAY_PART_LEN]; > + > + smp_rmb(); > + > return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] : NULL; > } > >
diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c index 8b644113715e..4f541e05cd3f 100644 --- a/net/8021q/vlan.c +++ b/net/8021q/vlan.c @@ -71,6 +71,8 @@ static int vlan_group_prealloc_vid(struct vlan_group *vg, if (array == NULL) return -ENOBUFS; + smp_wmb(); + vg->vlan_devices_arrays[pidx][vidx] = array; return 0; } diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h index 953405362795..7408fda084d3 100644 --- a/net/8021q/vlan.h +++ b/net/8021q/vlan.h @@ -57,6 +57,9 @@ static inline struct net_device *__vlan_group_get_device(struct vlan_group *vg, array = vg->vlan_devices_arrays[pidx] [vlan_id / VLAN_GROUP_ARRAY_PART_LEN]; + + smp_rmb(); + return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] : NULL; }