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bpf: Fix NULL pointer dereference in bpf_get_local_storage() helper

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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
This commit is contained in:
Yonghong Song 2021-03-22 22:51:46 -07:00 • committed by Alexei Starovoitov
parent a46410d5e4
commit b910eaaaa4
5 changed files with 86 additions and 19 deletions
Download patch file Download diff file Expand all files Collapse all files

57
include/linux/bpf-cgroup.h
View file

@ -20,14 +20,25 @@ struct bpf_sock_ops_kern;
struct bpf_cgroup_storage;
struct ctl_table;
struct ctl_table_header;
struct task_struct;
#ifdef CONFIG_CGROUP_BPF
extern struct static_key_false cgroup_bpf_enabled_key[MAX_BPF_ATTACH_TYPE];
#define cgroup_bpf_enabled(type) static_branch_unlikely(&cgroup_bpf_enabled_key[type])
DECLARE_PER_CPU(struct bpf_cgroup_storage*,
bpf_cgroup_storage[MAX_BPF_CGROUP_STORAGE_TYPE]);
#define BPF_CGROUP_STORAGE_NEST_MAX 8
struct bpf_cgroup_storage_info {
struct task_struct *task;
struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE];
};
/* For each cpu, permit maximum BPF_CGROUP_STORAGE_NEST_MAX number of tasks
* to use bpf cgroup storage simultaneously.
*/
DECLARE_PER_CPU(struct bpf_cgroup_storage_info,
bpf_cgroup_storage_info[BPF_CGROUP_STORAGE_NEST_MAX]);
#define for_each_cgroup_storage_type(stype) \
for (stype = 0; stype < MAX_BPF_CGROUP_STORAGE_TYPE; stype++)
@ -161,13 +172,42 @@ static inline enum bpf_cgroup_storage_type cgroup_storage_type(
return BPF_CGROUP_STORAGE_SHARED;
}
static inline void bpf_cgroup_storage_set(struct bpf_cgroup_storage
*storage[MAX_BPF_CGROUP_STORAGE_TYPE])
static inline int bpf_cgroup_storage_set(struct bpf_cgroup_storage
*storage[MAX_BPF_CGROUP_STORAGE_TYPE])
{
enum bpf_cgroup_storage_type stype;
int i, err = 0;
for_each_cgroup_storage_type(stype)
this_cpu_write(bpf_cgroup_storage[stype], storage[stype]);
preempt_disable();
for (i = 0; i < BPF_CGROUP_STORAGE_NEST_MAX; i++) {
if (unlikely(this_cpu_read(bpf_cgroup_storage_info[i].task) != NULL))
continue;
this_cpu_write(bpf_cgroup_storage_info[i].task, current);
for_each_cgroup_storage_type(stype)
this_cpu_write(bpf_cgroup_storage_info[i].storage[stype],
storage[stype]);
goto out;
}
err = -EBUSY;
WARN_ON_ONCE(1);
out:
preempt_enable();
return err;
}
static inline void bpf_cgroup_storage_unset(void)
{
int i;
for (i = 0; i < BPF_CGROUP_STORAGE_NEST_MAX; i++) {
if (unlikely(this_cpu_read(bpf_cgroup_storage_info[i].task) != current))
continue;
this_cpu_write(bpf_cgroup_storage_info[i].task, NULL);
return;
}
}
struct bpf_cgroup_storage *
@ -448,8 +488,9 @@ static inline int cgroup_bpf_prog_query(const union bpf_attr *attr,
return -EINVAL;
}
static inline void bpf_cgroup_storage_set(
struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE]) {}
static inline int bpf_cgroup_storage_set(
struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE]) { return 0; }
static inline void bpf_cgroup_storage_unset(void) {}
static inline int bpf_cgroup_storage_assign(struct bpf_prog_aux *aux,
struct bpf_map *map) { return 0; }
static inline struct bpf_cgroup_storage *bpf_cgroup_storage_alloc(