From d81ddadabdee32732477f9f85f1c7cec3c89b00f Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Mon, 23 Aug 2021 10:36:46 -0700 Subject: bpf: Fix NULL pointer dereference in bpf_get_local_storage() helper commit b910eaaaa4b89976ef02e5d6448f3f73dc671d91 upstream. Jiri Olsa reported a bug ([1]) in kernel where cgroup local storage pointer may be NULL in bpf_get_local_storage() helper. There are two issues uncovered by this bug: (1). kprobe or tracepoint prog incorrectly sets cgroup local storage before prog run, (2). due to change from preempt_disable to migrate_disable, preemption is possible and percpu storage might be overwritten by other tasks. This issue (1) is fixed in [2]. This patch tried to address issue (2). The following shows how things can go wrong: task 1: bpf_cgroup_storage_set() for percpu local storage preemption happens task 2: bpf_cgroup_storage_set() for percpu local storage preemption happens task 1: run bpf program task 1 will effectively use the percpu local storage setting by task 2 which will be either NULL or incorrect ones. Instead of just one common local storage per cpu, this patch fixed the issue by permitting 8 local storages per cpu and each local storage is identified by a task_struct pointer. This way, we allow at most 8 nested preemption between bpf_cgroup_storage_set() and bpf_cgroup_storage_unset(). The percpu local storage slot is released (calling bpf_cgroup_storage_unset()) by the same task after bpf program finished running. bpf_test_run() is also fixed to use the new bpf_cgroup_storage_set() interface. The patch is tested on top of [2] with reproducer in [1]. Without this patch, kernel will emit error in 2-3 minutes. With this patch, after one hour, still no error. [1] https://lore.kernel.org/bpf/CAKH8qBuXCfUz=w8L+Fj74OaUpbosO29niYwTki7e3Ag044_aww@mail.gmail.com/T [2] https://lore.kernel.org/bpf/20210309185028.3763817-1-yhs@fb.com Signed-off-by: Yonghong Song Signed-off-by: Alexei Starovoitov Acked-by: Roman Gushchin Link: https://lore.kernel.org/bpf/20210323055146.3334476-1-yhs@fb.com Cc: # 5.10.x Signed-off-by: Stanislav Fomichev Signed-off-by: Sasha Levin --- include/linux/bpf.h | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) (limited to 'include/linux/bpf.h') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index c3ccb242d199..3f93a50c25ef 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1089,9 +1089,14 @@ int bpf_prog_array_copy(struct bpf_prog_array *old_array, goto _out; \ _item = &_array->items[0]; \ while ((_prog = READ_ONCE(_item->prog))) { \ - if (set_cg_storage) \ - bpf_cgroup_storage_set(_item->cgroup_storage); \ - _ret &= func(_prog, ctx); \ + if (!set_cg_storage) { \ + _ret &= func(_prog, ctx); \ + } else { \ + if (unlikely(bpf_cgroup_storage_set(_item->cgroup_storage))) \ + break; \ + _ret &= func(_prog, ctx); \ + bpf_cgroup_storage_unset(); \ + } \ _item++; \ } \ _out: \ @@ -1135,8 +1140,10 @@ _out: \ _array = rcu_dereference(array); \ _item = &_array->items[0]; \ while ((_prog = READ_ONCE(_item->prog))) { \ - bpf_cgroup_storage_set(_item->cgroup_storage); \ + if (unlikely(bpf_cgroup_storage_set(_item->cgroup_storage))) \ + break; \ ret = func(_prog, ctx); \ + bpf_cgroup_storage_unset(); \ _ret &= (ret & 1); \ _cn |= (ret & 2); \ _item++; \ -- cgit v1.2.3