From b910eaaaa4b89976ef02e5d6448f3f73dc671d91 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Mon, 22 Mar 2021 22:51:46 -0700 Subject: bpf: Fix NULL pointer dereference in bpf_get_local_storage() helper 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 --- net/bpf/test_run.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'net/bpf') diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 0abdd67f44b1..4aabf71cd95d 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -106,12 +106,16 @@ static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat, bpf_test_timer_enter(&t); do { - 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(); } while (bpf_test_timer_continue(&t, repeat, &ret, time)); bpf_test_timer_leave(&t); -- cgit v1.2.3