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Date:   Thu, 29 Sep 2022 15:39:57 +0800
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To:     Theodore Ts'o <tytso@mit.edu>
CC:     <linux-ext4@vger.kernel.org>, <liuzhiqiang26@huawei.com>,
        linfeilong <linfeilong@huawei.com>
From:   zhanchengbin <zhanchengbin1@huawei.com>
Subject: [bug report] misc/fsck.c: Processes may kill other processes.
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Hi Tytso,
I find a error in misc/fsck.c, if run the fsck -N command, processes
don't execute, just show what would be done. However, the pid whose
value is -1 is added to the instance_list list in the execute
function,if the kill_all function is called later, kill(-1, signum)
is executed, Signals are sent to all processes except the number one
process and itself. Other processes will be killed if they use the
default signal processing function.

execute:
     if (noexecute)
         pid = -1;
     inst->pid = pid;
     // Find the end of the list, so we add the instance on at the end.

kill_all:
     for (inst = instance_list; inst; inst = inst->next) {
         kill(inst->pid, signum);
     }

misc/fsck.c:
main:
     ->PRS
         case 'N':
             noexecute++;
     for (num_devices) {
         if (cancel_requested) {
             ->kill_all(SIGTERM);
         }
         ->fsck_device
             ->execute
     }

(gdb) bt
#0  execute (type=<optimized out>, type@entry=0x412cd0 "ext4", 
device=0x412b00 "/root/a.img", mntpt=<optimized out>, 
interactive=interactive@entry=1) at fsck.c:523
#1  0x0000000000404959 in fsck_device (fs=fs@entry=0x412ac0, 
interactive=interactive@entry=1) at fsck.c:727
#2  0x0000000000402704 in main (argc=<optimized out>, argv=<optimized 
out>) at fsck.c:1333
(gdb) p inst->pid
$7 = -1

regards,
Zhan Chengbin