84258438e8
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: d2ba09c17a ("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>
120 lines
2.5 KiB
C
120 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/umh.h>
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#include <linux/bpfilter.h>
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#include <linux/sched.h>
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#include <linux/sched/signal.h>
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#include <linux/fs.h>
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#include <linux/file.h>
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#include "msgfmt.h"
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extern char bpfilter_umh_start;
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extern char bpfilter_umh_end;
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static struct umh_info info;
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/* since ip_getsockopt() can run in parallel, serialize access to umh */
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static DEFINE_MUTEX(bpfilter_lock);
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static void shutdown_umh(struct umh_info *info)
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{
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struct task_struct *tsk;
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if (!info->pid)
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return;
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tsk = get_pid_task(find_vpid(info->pid), PIDTYPE_PID);
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if (tsk) {
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force_sig(SIGKILL, tsk);
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put_task_struct(tsk);
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}
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fput(info->pipe_to_umh);
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fput(info->pipe_from_umh);
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info->pid = 0;
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}
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static void __stop_umh(void)
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{
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if (IS_ENABLED(CONFIG_INET)) {
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bpfilter_process_sockopt = NULL;
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shutdown_umh(&info);
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}
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}
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static void stop_umh(void)
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{
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mutex_lock(&bpfilter_lock);
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__stop_umh();
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mutex_unlock(&bpfilter_lock);
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}
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static int __bpfilter_process_sockopt(struct sock *sk, int optname,
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char __user *optval,
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unsigned int optlen, bool is_set)
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{
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struct mbox_request req;
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struct mbox_reply reply;
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loff_t pos;
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ssize_t n;
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int ret = -EFAULT;
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req.is_set = is_set;
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req.pid = current->pid;
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req.cmd = optname;
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req.addr = (long __force __user)optval;
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req.len = optlen;
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mutex_lock(&bpfilter_lock);
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if (!info.pid)
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goto out;
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n = __kernel_write(info.pipe_to_umh, &req, sizeof(req), &pos);
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if (n != sizeof(req)) {
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pr_err("write fail %zd\n", n);
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__stop_umh();
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ret = -EFAULT;
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goto out;
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}
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pos = 0;
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n = kernel_read(info.pipe_from_umh, &reply, sizeof(reply), &pos);
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if (n != sizeof(reply)) {
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pr_err("read fail %zd\n", n);
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__stop_umh();
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ret = -EFAULT;
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goto out;
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}
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ret = reply.status;
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out:
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mutex_unlock(&bpfilter_lock);
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return ret;
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}
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static int __init load_umh(void)
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{
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int err;
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/* fork usermode process */
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err = fork_usermode_blob(&bpfilter_umh_start,
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&bpfilter_umh_end - &bpfilter_umh_start,
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&info);
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if (err)
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return err;
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pr_info("Loaded bpfilter_umh pid %d\n", info.pid);
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/* health check that usermode process started correctly */
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if (__bpfilter_process_sockopt(NULL, 0, NULL, 0, 0) != 0) {
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stop_umh();
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return -EFAULT;
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}
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if (IS_ENABLED(CONFIG_INET))
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bpfilter_process_sockopt = &__bpfilter_process_sockopt;
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return 0;
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}
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static void __exit fini_umh(void)
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{
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stop_umh();
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}
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module_init(load_umh);
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module_exit(fini_umh);
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MODULE_LICENSE("GPL");
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