4.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Taehee Yoo <ap420073@xxxxxxxxx>
[ Upstream commit 84258438e8ce12d6888b68a1238bba9cb25307e2 ]
pid_task() dereferences rcu protected tasks array.
But there is no rcu_read_lock() in shutdown_umh() routine so that
rcu_read_lock() is needed.
get_pid_task() is wrapper function of pid_task. it holds rcu_read_lock()
then calls pid_task(). if task isn't NULL, it increases reference count
of task.
test commands:
%modprobe bpfilter
%modprobe -rv bpfilter
splat looks like:
[15102.030932] =============================
[15102.030957] WARNING: suspicious RCU usage
[15102.030985] 4.19.0-rc7+ #21 Not tainted
[15102.031010] -----------------------------
[15102.031038] kernel/pid.c:330 suspicious rcu_dereference_check() usage!
[15102.031063]
other info that might help us debug this:
[15102.031332]
rcu_scheduler_active = 2, debug_locks = 1
[15102.031363] 1 lock held by modprobe/1570:
[15102.031389] #0: 00000000580ef2b0 (bpfilter_lock){+.+.}, at: stop_umh+0x13/0x52 [bpfilter]
[15102.031552]
stack backtrace:
[15102.031583] CPU: 1 PID: 1570 Comm: modprobe Not tainted 4.19.0-rc7+ #21
[15102.031607] Hardware name: To be filled by O.E.M. To be filled by O.E.M./Aptio CRB, BIOS 5.6.5 07/08/2015
[15102.031628] Call Trace:
[15102.031676] dump_stack+0xc9/0x16b
[15102.031723] ? show_regs_print_info+0x5/0x5
[15102.031801] ? lockdep_rcu_suspicious+0x117/0x160
[15102.031855] pid_task+0x134/0x160
[15102.031900] ? find_vpid+0xf0/0xf0
[15102.032017] shutdown_umh.constprop.1+0x1e/0x53 [bpfilter]
[15102.032055] stop_umh+0x46/0x52 [bpfilter]
[15102.032092] __x64_sys_delete_module+0x47e/0x570
[ ... ]
Fixes: d2ba09c17a06 ("net: add skeleton of bpfilter kernel module")
Signed-off-by: Taehee Yoo <ap420073@xxxxxxxxx>
Acked-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/bpfilter/bpfilter_kern.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- a/net/bpfilter/bpfilter_kern.c
+++ b/net/bpfilter/bpfilter_kern.c
@@ -23,9 +23,11 @@ static void shutdown_umh(struct umh_info
if (!info->pid)
return;
- tsk = pid_task(find_vpid(info->pid), PIDTYPE_PID);
- if (tsk)
+ tsk = get_pid_task(find_vpid(info->pid), PIDTYPE_PID);
+ if (tsk) {
force_sig(SIGKILL, tsk);
+ put_task_struct(tsk);
+ }
fput(info->pipe_to_umh);
fput(info->pipe_from_umh);
info->pid = 0;
