4.18-stable review patch. If anyone has any objections, please let me know.
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From: Taehee Yoo ap420073@gmail.com
[ 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@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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;