net, bpf: Fix RCU usage in task_cls_state() for BPF programs

The commit ee971630f20f ("bpf: Allow some trace helpers for all prog
types") made bpf_get_cgroup_classid_curr helper available to all BPF
program types, not just networking programs.

This helper calls __task_get_classid() which internally calls
task_cls_state() requiring rcu_read_lock_bh_held(). This works
in networking/tc context where RCU BH is held, but triggers an RCU
warning when called from other contexts like BPF syscall programs
that run under rcu_read_lock_trace():

  WARNING: suspicious RCU usage
  6.15.0-rc4-syzkaller-g079e5c56a5c4 #0 Not tainted
  -----------------------------
  net/core/netclassid_cgroup.c:24 suspicious rcu_dereference_check() usage!

Fix this by also accepting rcu_read_lock_held() and
rcu_read_lock_trace_held() as valid RCU contexts in the
task_cls_state() function. This ensures the helper works correctly
in all needed RCU contexts where it might be called, regular RCU,
RCU BH (for networking), and RCU trace (for BPF syscall programs).

Fixes: ee971630f20f ("bpf: Allow some trace helpers for all prog types")
Reported-by: syzbot+b4169a1cfb945d2ed0ec@syzkaller.appspotmail.com
Signed-off-by: Charalampos Mitrodimas <charmitro@posteo.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20250611-rcu-fix-task_cls_state-v3-1-3d30e1de753f@posteo.net
Closes: https://syzkaller.appspot.com/bug?extid=b4169a1cfb945d2ed0ec

diff --git a/net/core/netclassid_cgroup.c b/net/core/netclassid_cgroup.c
index d22f0919821e931fbdedf5a8a7a2998d59d73978..dff66d8fb325d28bb15f42641b9ec738b0022353 100644 (file)
--- a/net/core/netclassid_cgroup.c
+++ b/net/core/netclassid_cgroup.c
@@ -21,7 +21,9 @@ static inline struct cgroup_cls_state *css_cls_state(struct cgroup_subsys_state
 struct cgroup_cls_state *task_cls_state(struct task_struct *p)
 {
        return css_cls_state(task_css_check(p, net_cls_cgrp_id,
-                                           rcu_read_lock_bh_held()));
+                                           rcu_read_lock_held() ||
+                                           rcu_read_lock_bh_held() ||
+                                           rcu_read_lock_trace_held()));
 }
 EXPORT_SYMBOL_GPL(task_cls_state);