6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Yafang Shao laoar.shao@gmail.com
[ Upstream commit 29a7e00ffadddd8d68eff311de1bf12ae10687bb ]
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:
[ 1259.662357] 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!
Other info that might help to 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
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 Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Stanislav Fomichev sdf@google.com Cc: Feng Zhou zhoufeng.zf@bytedance.com Cc: KP Singh kpsingh@kernel.org Link: https://lore.kernel.org/bpf/20231007135945.4306-1-laoar.shao@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/helpers.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 8bd3812fb8df4..68f54e16c7be0 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -2197,7 +2197,12 @@ __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 */