From: Yonghong Song yhs@fb.com

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_... [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 Change-Id: I0bff719d0bfbaa819316de26391b4b2e4e60faed Signed-off-by: Stanislav Fomichev sdf@google.com --- include/linux/bpf-cgroup.h | 57 ++++++++++++++++++++++++++++++++------ include/linux/bpf.h | 15 +++++++--- kernel/bpf/helpers.c | 15 +++++++--- kernel/bpf/local_storage.c | 5 ++-- net/bpf/test_run.c | 6 +++- 5 files changed, 79 insertions(+), 19 deletions(-)

diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h index ed71bd1a0825..53f14e8827cc 100644 --- a/include/linux/bpf-cgroup.h +++ b/include/linux/bpf-cgroup.h @@ -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; #define cgroup_bpf_enabled static_branch_unlikely(&cgroup_bpf_enabled_key)

-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++) @@ -156,13 +167,42 @@ 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; + + 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;

- for_each_cgroup_storage_type(stype) - this_cpu_write(bpf_cgroup_storage[stype], storage[stype]); + this_cpu_write(bpf_cgroup_storage_info[i].task, NULL); + return; + } }

struct bpf_cgroup_storage * @@ -410,8 +450,9 @@ 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( 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++; \ diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index f7e99bb8c3b6..3bd7fbd8c543 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -372,8 +372,8 @@ const struct bpf_func_proto bpf_get_current_ancestor_cgroup_id_proto = { };

#ifdef CONFIG_CGROUP_BPF -DECLARE_PER_CPU(struct bpf_cgroup_storage*, - bpf_cgroup_storage[MAX_BPF_CGROUP_STORAGE_TYPE]); +DECLARE_PER_CPU(struct bpf_cgroup_storage_info, + bpf_cgroup_storage_info[BPF_CGROUP_STORAGE_NEST_MAX]);

BPF_CALL_2(bpf_get_local_storage, struct bpf_map *, map, u64, flags) { @@ -382,10 +382,17 @@ BPF_CALL_2(bpf_get_local_storage, struct bpf_map *, map, u64, flags) * verifier checks that its value is correct. */ enum bpf_cgroup_storage_type stype = cgroup_storage_type(map); - struct bpf_cgroup_storage *storage; + struct bpf_cgroup_storage *storage = NULL; void *ptr; + int i;

- storage = this_cpu_read(bpf_cgroup_storage[stype]); + for (i = 0; i < BPF_CGROUP_STORAGE_NEST_MAX; i++) { + if (unlikely(this_cpu_read(bpf_cgroup_storage_info[i].task) != current)) + continue; + + storage = this_cpu_read(bpf_cgroup_storage_info[i].storage[stype]); + break; + }

if (stype == BPF_CGROUP_STORAGE_SHARED) ptr = &READ_ONCE(storage->buf)->data[0]; diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c index 571bb351ed3b..b139247d2dd3 100644 --- a/kernel/bpf/local_storage.c +++ b/kernel/bpf/local_storage.c @@ -9,10 +9,11 @@ #include <linux/slab.h> #include <uapi/linux/btf.h>

-DEFINE_PER_CPU(struct bpf_cgroup_storage*, bpf_cgroup_storage[MAX_BPF_CGROUP_STORAGE_TYPE]); - #ifdef CONFIG_CGROUP_BPF

+DEFINE_PER_CPU(struct bpf_cgroup_storage_info, + bpf_cgroup_storage_info[BPF_CGROUP_STORAGE_NEST_MAX]); + #include "../cgroup/cgroup-internal.h"

#define LOCAL_STORAGE_CREATE_FLAG_MASK \ diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index e7cbd1b4a5e5..72d424a5a142 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -42,13 +42,17 @@ static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat, migrate_disable(); time_start = ktime_get_ns(); for (i = 0; i < repeat; i++) { - bpf_cgroup_storage_set(storage); + ret = bpf_cgroup_storage_set(storage); + if (ret) + break;

if (xdp) *retval = bpf_prog_run_xdp(prog, ctx); else *retval = BPF_PROG_RUN(prog, ctx);

+ bpf_cgroup_storage_unset(); + if (signal_pending(current)) { ret = -EINTR; break;