Commit bf956be5 authored Jun 07, 2018 by Alexei Starovoitov Committed by David S. Miller Jun 07, 2018

umh: fix race condition



kasan reported use-after-free:
BUG: KASAN: use-after-free in call_usermodehelper_exec_work+0x2d3/0x310 kernel/umh.c:195
Write of size 4 at addr ffff8801d9202370 by task kworker/u4:2/50
Workqueue: events_unbound call_usermodehelper_exec_work
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b9/0x294 lib/dump_stack.c:113
 print_address_description+0x6c/0x20b mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
 __asan_report_store4_noabort+0x17/0x20 mm/kasan/report.c:437
 call_usermodehelper_exec_work+0x2d3/0x310 kernel/umh.c:195
 process_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
 worker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
 kthread+0x345/0x410 kernel/kthread.c:240
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412

The reason is that 'sub_info' cannot be accessed out of parent task
context, since it will be freed by the child.
Instead remember the pid in the child task.

Fixes: 449325b5 ("umh: introduce fork_usermode_blob() helper")
Reported-by:  <syzbot+2c73319c406f1987d156@syzkaller.appspotmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 2ac0e152

kernel/umh.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -99,6 +99,7 @@ static int call_usermodehelper_exec_async(void *data)

		commit_creds(new);

		sub_info->pid = task_pid_nr(current);
		if (sub_info->file)
		retval = do_execve_file(sub_info->file,
		sub_info->argv, sub_info->envp);
		@@ -191,8 +192,6 @@ static void call_usermodehelper_exec_work(struct work_struct *work)
		if (pid < 0) {
		sub_info->retval = pid;
		umh_complete(sub_info);
		} else {
		sub_info->pid = pid;
		}
		}
		}

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