• Alexei Starovoitov's avatar
    umh: fix race condition · bf956be5
    Alexei Starovoitov authored
    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: 's avatarAlexei Starovoitov <ast@kernel.org>
    Signed-off-by: 's avatarDavid S. Miller <davem@davemloft.net>
    bf956be5
umh.c 18 KB