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bpf: Fix NULL pointer dereference in bpf_get_local_storage() helper

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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 <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Roman Gushchin <guro@fb.com>
Link: https://lore.kernel.org/bpf/20210323055146.3334476-1-yhs@fb.com
Cc: <stable@vger.kernel.org> # 5.10.x
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Yonghong Song
2021-08-23 10:36:46 -07:00
committed by Greg Kroah-Hartman
parent 9dd6f6d896
commit d81ddadabd
5 changed files with 79 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
include/linux/bpf.h
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@@ -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++; \