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authorYonghong Song <yhs@fb.com>2021-03-22 22:51:46 -0700
committerAlexei Starovoitov <ast@kernel.org>2021-03-25 18:31:36 -0700
commitb910eaaaa4b89976ef02e5d6448f3f73dc671d91 (patch)
treed1173cd95a51900b2b257f0a97e9e09369e439de /net/bpf
parenta46410d5e4975d701d526397156fa0815747dc2f (diff)
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 <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
Diffstat (limited to 'net/bpf')
-rw-r--r--net/bpf/test_run.c6
1 files changed, 5 insertions, 1 deletions
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);