| Message ID | 20231007135945.4306-1-laoar.shao@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 29a7e00ffadddd8d68eff311de1bf12ae10687bb |
| Delegated to: | BPF |
| Headers | show |
| Series | [bpf-next,v2,1/2] bpf: Fix missed rcu read lock in bpf_task_under_cgroup() | expand |
Hello: This series was applied to bpf/bpf-next.git (master) by Daniel Borkmann <daniel@iogearbox.net>: On Sat, 7 Oct 2023 13:59:44 +0000 you wrote: > When employed within a sleepable program not under RCU protection, the use > of 'bpf_task_under_cgroup()' may trigger a warning in the kernel log, > particularly when CONFIG_PROVE_RCU is enabled. > > [ 1259.662354] ============================= > [ 1259.662357] WARNING: suspicious RCU usage > [ 1259.662358] 6.5.0+ #33 Not tainted > [ 1259.662360] ----------------------------- > [ 1259.662361] include/linux/cgroup.h:423 suspicious rcu_dereference_check() usage! > [ 1259.662364] > other info that might help us debug this: > > [...] Here is the summary with links: - [bpf-next,v2,1/2] bpf: Fix missed rcu read lock in bpf_task_under_cgroup() https://git.kernel.org/bpf/bpf-next/c/29a7e00ffadd - [bpf-next,v2,2/2] selftests/bpf: Add selftest for bpf_task_under_cgroup() in sleepable prog https://git.kernel.org/bpf/bpf-next/c/44cb03f19b38 You are awesome, thank you!
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index dd1c69ee3375..bb521b181cc3 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -2212,7 +2212,12 @@ __bpf_kfunc struct cgroup *bpf_cgroup_from_id(u64 cgid) __bpf_kfunc long bpf_task_under_cgroup(struct task_struct *task, struct cgroup *ancestor) { - return task_under_cgroup_hierarchy(task, ancestor); + long ret; + + rcu_read_lock(); + ret = task_under_cgroup_hierarchy(task, ancestor); + rcu_read_unlock(); + return ret; } #endif /* CONFIG_CGROUPS */
When employed within a sleepable program not under RCU protection, the use of 'bpf_task_under_cgroup()' may trigger a warning in the kernel log, particularly when CONFIG_PROVE_RCU is enabled. [ 1259.662354] ============================= [ 1259.662357] WARNING: suspicious RCU usage [ 1259.662358] 6.5.0+ #33 Not tainted [ 1259.662360] ----------------------------- [ 1259.662361] include/linux/cgroup.h:423 suspicious rcu_dereference_check() usage! [ 1259.662364] other info that might help us debug this: [ 1259.662366] rcu_scheduler_active = 2, debug_locks = 1 [ 1259.662368] 1 lock held by trace/72954: [ 1259.662369] #0: ffffffffb5e3eda0 (rcu_read_lock_trace){....}-{0:0}, at: __bpf_prog_enter_sleepable+0x0/0xb0 [ 1259.662383] stack backtrace: [ 1259.662385] CPU: 50 PID: 72954 Comm: trace Kdump: loaded Not tainted 6.5.0+ #33 [ 1259.662391] Call Trace: [ 1259.662393] <TASK> [ 1259.662395] dump_stack_lvl+0x6e/0x90 [ 1259.662401] dump_stack+0x10/0x20 [ 1259.662404] lockdep_rcu_suspicious+0x163/0x1b0 [ 1259.662412] task_css_set.part.0+0x23/0x30 [ 1259.662417] bpf_task_under_cgroup+0xe7/0xf0 [ 1259.662422] bpf_prog_7fffba481a3bcf88_lsm_run+0x5c/0x93 [ 1259.662431] bpf_trampoline_6442505574+0x60/0x1000 [ 1259.662439] bpf_lsm_bpf+0x5/0x20 [ 1259.662443] ? security_bpf+0x32/0x50 [ 1259.662452] __sys_bpf+0xe6/0xdd0 [ 1259.662463] __x64_sys_bpf+0x1a/0x30 [ 1259.662467] do_syscall_64+0x38/0x90 [ 1259.662472] entry_SYSCALL_64_after_hwframe+0x6e/0xd8 [ 1259.662479] RIP: 0033:0x7f487baf8e29 ... [ 1259.662504] </TASK> This issue can be reproduced by executing a straightforward program, as demonstrated below: SEC("lsm.s/bpf") int BPF_PROG(lsm_run, int cmd, union bpf_attr *attr, unsigned int size) { struct cgroup *cgrp = NULL; struct task_struct *task; int ret = 0; if (cmd != BPF_LINK_CREATE) return 0; // The cgroup2 should be mounted first cgrp = bpf_cgroup_from_id(1); if (!cgrp) goto out; task = bpf_get_current_task_btf(); if (bpf_task_under_cgroup(task, cgrp)) ret = -1; bpf_cgroup_release(cgrp); out: return ret; } After running the program, if you subsequently execute another BPF program, you will encounter the warning. It's worth noting that task_under_cgroup_hierarchy() is also utilized by bpf_current_task_under_cgroup(). However, bpf_current_task_under_cgroup() doesn't exhibit this issue because it cannot be used in sleepable BPF programs. Fixes: b5ad4cdc46c7 ("bpf: Add bpf_task_under_cgroup() kfunc") Signed-off-by: Yafang Shao <laoar.shao@gmail.com> Acked-by: Stanislav Fomichev <sdf@google.com> Cc: Feng Zhou <zhoufeng.zf@bytedance.com> --- kernel/bpf/helpers.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)