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SubjectRe: [PATCH net-next] umh: fix race condition
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From: Alexei Starovoitov <ast@kernel.org>
Date: Thu, 7 Jun 2018 10:23:10 -0700

> 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: 449325b52b7a ("umh: introduce fork_usermode_blob() helper")
> Reported-by: syzbot+2c73319c406f1987d156@syzkaller.appspotmail.com
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Applied.

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