bpf_task_from_vpid() looks up a task in the pid namespace of the
current task, via find_task_by_vpid():
find_task_by_vpid(vpid)
find_task_by_pid_ns(vpid, task_active_pid_ns(current))
find_pid_ns(nr, ns) -> idr_find(&ns->idr, nr)
cgroup_skb programs run in softirq, which may interrupt a task that is
itself in do_exit(). Once that task has passed
exit_notify() -> release_task() -> __unhash_process(), its thread_pid is
cleared, so task_active_pid_ns(current) returns NULL and find_pid_ns()
dereferences &NULL->idr:
BUG: kernel NULL pointer dereference, address: 0000000000000050
RIP: 0010:idr_find+0x11/0x30 lib/idr.c:176
Call Trace:
find_pid_ns kernel/pid.c:370 [inline]
find_task_by_pid_ns+0x3b/0xe0 kernel/pid.c:485
bpf_task_from_vpid+0x5b/0x200 kernel/bpf/helpers.c:2916
bpf_prog_run_array_cg+0x17e/0x530 kernel/bpf/cgroup.c:81
__cgroup_bpf_run_filter_skb+0x12b/0x250 kernel/bpf/cgroup.c:1612
sk_filter_trim_cap+0x1dc/0x4c0 net/core/filter.c:148
tcp_v4_rcv+0x18d1/0x2200 net/ipv4/tcp_ipv4.c:2223
do_exit+0xa63/0x1270 kernel/exit.c:1010
get_signal+0x141c/0x1530 kernel/signal.c:3037
Bail out when current has no pid namespace.
Fixes: 675c3596ff32 ("bpf: Add bpf_task_from_vpid() kfunc")
Signed-off-by: Sechang Lim
---
kernel/bpf/helpers.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index b5314c9fed3c..4646a915bf98 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2913,6 +2913,10 @@ __bpf_kfunc struct task_struct *bpf_task_from_vpid(s32 vpid)
struct task_struct *p;
rcu_read_lock();
+ if (!task_active_pid_ns(current)) {
+ rcu_read_unlock();
+ return NULL;
+ }
p = find_task_by_vpid(vpid);
if (p)
p = bpf_task_acquire(p);
--
2.43.0