This is a note to let you know that I've just added the patch titled
bpf: Fix missed rcu read lock in bpf_task_under_cgroup()
to the 6.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bpf-fix-missed-rcu-read-lock-in-bpf_task_under_cgrou.patch
and it can be found in the queue-6.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 913ae1086d707fa8cafb5ed17b4bbf54e65840b8
Author: Yafang Shao <laoar.shao@xxxxxxxxx>
Date: Sat Oct 7 13:59:44 2023 +0000
bpf: Fix missed rcu read lock in bpf_task_under_cgroup()
[ 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@xxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
Cc: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>
Cc: KP Singh <kpsingh@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20231007135945.4306-1-laoar.shao@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 8812397a5cd96..3779300002327 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2167,7 +2167,12 @@ __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 */
