Yes, you are absolutely correct. I can reproduce this now, when
kernel.core_pattern is set to "|".

I can also confirm that the first kernel that this is broken in is 5.3,
as it works fine in 5.2 and below.

I will look into this and hopefully get this fixed for you. Thanks for
reporting!

Engineering Notes:

RIP: 0010:do_coredump+0x536/0xb30

$ eu-addr2line do_coredump+0x536 -e vmlinux-5.3.0-29-generic 
/build/linux-OZAq_R/linux-5.3.0/include/linux/fs.h:2841:7

This is the function file_start_write():

2839 static inline void file_start_write(struct file *file)
2840 {
2841     if (!S_ISREG(file_inode(file)->i_mode))
2842         return;
2843     __sb_start_write(file_inode(file)->i_sb, SB_FREEZE_WRITE, true);
2844 }

This is called from do_coredump():

565 void do_coredump(const kernel_siginfo_t *siginfo)
566 {
...
788     if (!dump_interrupted()) {
789         file_start_write(cprm.file);
790         core_dumped = binfmt->core_dump(&cprm);
791         file_end_write(cprm.file);
792     }
...
810 }

On kernels 5.2 and before, kernel.core_pattern=| normally outputs:

[   39.328638] Core dump to | pipe failed

This is output is from the pipe section of do_coredump():

565 void do_coredump(const kernel_siginfo_t *siginfo)
566 {
...
623     ispipe = format_corename(&cn, &cprm, &argv, &argc);
624 
625     if (ispipe) {
...
681         sub_info = call_usermodehelper_setup(helper_argv[0],
682                         helper_argv, NULL, GFP_KERNEL,
683                         umh_pipe_setup, NULL, &cprm);
684         if (sub_info)
685             retval = call_usermodehelper_exec(sub_info,
686                               UMH_WAIT_EXEC);
687 
688         kfree(helper_argv);
689         if (retval) {
690             printk(KERN_INFO "Core dump to |%s pipe failed\n",
691                    cn.corename);
692             goto close_fail;
693         }
...
810 }

With kernel.core_pattern=|, format_corename() still interprets this as
the pipe path with:

191 static int format_corename(struct core_name *cn, struct coredump_params 
*cprm,
192                size_t **argv, int *argc)
193 {
...
196     int ispipe = (*pat_ptr == '|');
...
335     return ispipe;
336 }

Which checks the first byte of the core_pattern string to see if it is a
"|".

This means we really want the call to call_usermodehelper_exec() in
do_coredump() to fail, so we take the if(retval) step and output "Core
dump to |%s pipe failed\n".

Note that cn.corename is NULL when kernel.core_pattern=|.

For some reason with 5.3 and later, this call to
call_usermodehelper_exec() is not failing, and execution continues on
and breaks at file_start_write(cprm.file); at the end of do_coredump().

call_usermodehelper_exec() calls umh_pipe_setup() and creates the pipe
used. Something has likely changed in the pipe subsystem.

I will update when I figure out what.

** Also affects: linux (Ubuntu Eoan)
   Importance: Undecided
       Status: New

** Also affects: linux (Ubuntu Focal)
   Importance: Undecided
       Status: Confirmed

** Changed in: linux (Ubuntu Eoan)
       Status: New => Confirmed

** Changed in: linux (Ubuntu Eoan)
   Importance: Undecided => Medium

** Changed in: linux (Ubuntu Focal)
   Importance: Undecided => Medium

** Changed in: linux (Ubuntu Eoan)
     Assignee: (unassigned) => Matthew Ruffell (mruffell)

** Changed in: linux (Ubuntu Focal)
     Assignee: (unassigned) => Matthew Ruffell (mruffell)

** Description changed:

  If process that listens socket on any port crashes (segmentation fault) it 
becomes unkillable.
  Kill command does not kill this process.
  Port that listen crashed process never be freed.
  
  journalctl shows error:
  
  Feb 13 13:28:09 vbun04 kernel: socktest[1359]: segfault at 21 ip 
000055ec3a6bf11e sp 00007ffd88899fb0 error 6 in socktest[55ec3a6bf000+1000]
  Feb 13 13:28:09 vbun04 kernel: Code: 04 24 02 00 17 70 89 c5 48 b8 30 30 30 
30 30 30 30 30 89 ef 48 89 44 24 08 e8 8e ff ff ff be 0a 00 00 00 89 ef e8 72 
ff ff ff <c7> 04 25 21 00 00 00 21 00 00 00 48 8b 44 24 18
  Feb 13 13:28:09 vbun04 kernel: BUG: kernel NULL pointer dereference, address: 
0000000000000020
  Feb 13 13:28:09 vbun04 kernel: #PF: supervisor read access in kernel mode
  Feb 13 13:28:09 vbun04 kernel: #PF: error_code(0x0000) - not-present page
  Feb 13 13:28:09 vbun04 kernel: PGD 0 P4D 0
  Feb 13 13:28:09 vbun04 kernel: Oops: 0000 [#1] SMP NOPTI
  Feb 13 13:28:09 vbun04 kernel: CPU: 1 PID: 1359 Comm: socktest Tainted: G     
      OE     5.3.0-29-generic #31-Ubuntu
  Feb 13 13:28:09 vbun04 kernel: Hardware name: innotek GmbH 
VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
  Feb 13 13:28:09 vbun04 kernel: RIP: 0010:do_coredump+0x536/0xb30
  Feb 13 13:28:09 vbun04 kernel: Code: 00 48 8b bd 18 ff ff ff 48 85 ff 74 05 
e8 c2 47 fa ff 65 48 8b 04 25 c0 6b 01 00 48 8b 00 48 8b 7d a0 a8 04 0f 85 65 
05 00 00 <48> 8b 57 20 0f b7 02 66 25 00 f0 66 3d 00 80 0f
  Feb 13 13:28:09 vbun04 kernel: RSP: 0000:ffffb464c2c5fca8 EFLAGS: 00010246
  Feb 13 13:28:09 vbun04 kernel: RAX: 0000000000000000 RBX: ffff9d4b76995100 
RCX: 0000000000001afc
  Feb 13 13:28:09 vbun04 kernel: RDX: 0000000000000000 RSI: ffffb464c2c5fc68 
RDI: 0000000000000000
  Feb 13 13:28:09 vbun04 kernel: RBP: ffffb464c2c5fdd8 R08: 0000000000000400 
R09: ffffb464c2c5fbe0
  Feb 13 13:28:09 vbun04 kernel: R10: ffff9d4b75d01170 R11: 0000000000000000 
R12: ffff9d4b7b3df540
  Feb 13 13:28:09 vbun04 kernel: R13: 0000000000000001 R14: 0000000000000000 
R15: ffffffffb9f15920
  Feb 13 13:28:09 vbun04 kernel: FS:  00007f6c91911540(0000) 
GS:ffff9d4b7db00000(0000) knlGS:0000000000000000
  Feb 13 13:28:09 vbun04 kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 
0000000080050033
  Feb 13 13:28:09 vbun04 kernel: CR2: 0000000000000020 CR3: 00000000723ac003 
CR4: 00000000000606e0
  Feb 13 13:28:09 vbun04 kernel: Call Trace:
  Feb 13 13:28:09 vbun04 kernel:  ? wake_up_state+0x10/0x20
  Feb 13 13:28:09 vbun04 kernel:  ? __send_signal+0x1eb/0x3f0
  Feb 13 13:28:09 vbun04 kernel:  get_signal+0x159/0x880
  Feb 13 13:28:09 vbun04 kernel:  do_signal+0x34/0x280
  Feb 13 13:28:09 vbun04 kernel:  ? bad_area+0x47/0x50
  Feb 13 13:28:09 vbun04 kernel:  exit_to_usermode_loop+0xbf/0x160
  Feb 13 13:28:09 vbun04 kernel:  prepare_exit_to_usermode+0x77/0xa0
  Feb 13 13:28:09 vbun04 kernel:  retint_user+0x8/0x8
  Feb 13 13:28:09 vbun04 kernel: RIP: 0033:0x55ec3a6bf11e
  Feb 13 13:28:09 vbun04 kernel: Code: 04 24 02 00 17 70 89 c5 48 b8 30 30 30 
30 30 30 30 30 89 ef 48 89 44 24 08 e8 8e ff ff ff be 0a 00 00 00 89 ef e8 72 
ff ff ff <c7> 04 25 21 00 00 00 21 00 00 00 48 8b 44 24 18
  Feb 13 13:28:09 vbun04 kernel: RSP: 002b:00007ffd88899fb0 EFLAGS: 00010217
  Feb 13 13:28:09 vbun04 kernel: RAX: 0000000000000000 RBX: 0000000000000000 
RCX: 00007f6c918424eb
  Feb 13 13:28:09 vbun04 kernel: RDX: 0000000000000010 RSI: 000000000000000a 
RDI: 0000000000000003
  Feb 13 13:28:09 vbun04 kernel: RBP: 0000000000000003 R08: 0000000000000000 
R09: 00007f6c919331f0
  Feb 13 13:28:09 vbun04 kernel: R10: 0000000000000000 R11: 0000000000000217 
R12: 000055ec3a6bf150
  Feb 13 13:28:09 vbun04 kernel: R13: 00007ffd8889a0b0 R14: 0000000000000000 
R15: 0000000000000000
  Feb 13 13:28:09 vbun04 kernel: Modules linked in: vboxsf(OE) nls_utf8 isofs 
vboxvideo(OE) intel_rapl_msr intel_rapl_common crct10dif_pclmul vmwgfx 
crc32_pclmul ghash_clmulni_intel aesni_intel ttm drm_kms_helper a
  Feb 13 13:28:09 vbun04 kernel: CR2: 0000000000000020
  Feb 13 13:28:09 vbun04 kernel: ---[ end trace 278d665c8727286a ]---
  Feb 13 13:28:09 vbun04 kernel: RIP: 0010:do_coredump+0x536/0xb30
  Feb 13 13:28:09 vbun04 kernel: Code: 00 48 8b bd 18 ff ff ff 48 85 ff 74 05 
e8 c2 47 fa ff 65 48 8b 04 25 c0 6b 01 00 48 8b 00 48 8b 7d a0 a8 04 0f 85 65 
05 00 00 <48> 8b 57 20 0f b7 02 66 25 00 f0 66 3d 00 80 0f
  Feb 13 13:28:09 vbun04 kernel: RSP: 0000:ffffb464c2c5fca8 EFLAGS: 00010246
  Feb 13 13:28:09 vbun04 kernel: RAX: 0000000000000000 RBX: ffff9d4b76995100 
RCX: 0000000000001afc
  Feb 13 13:28:09 vbun04 kernel: RDX: 0000000000000000 RSI: ffffb464c2c5fc68 
RDI: 0000000000000000
  Feb 13 13:28:09 vbun04 kernel: RBP: ffffb464c2c5fdd8 R08: 0000000000000400 
R09: ffffb464c2c5fbe0
  Feb 13 13:28:09 vbun04 kernel: R10: ffff9d4b75d01170 R11: 0000000000000000 
R12: ffff9d4b7b3df540
  Feb 13 13:28:09 vbun04 kernel: R13: 0000000000000001 R14: 0000000000000000 
R15: ffffffffb9f15920
  Feb 13 13:28:09 vbun04 kernel: FS:  00007f6c91911540(0000) 
GS:ffff9d4b7db00000(0000) knlGS:0000000000000000
  Feb 13 13:28:09 vbun04 kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 
0000000080050033
  Feb 13 13:28:09 vbun04 kernel: CR2: 0000000000000020 CR3: 00000000723ac003 
CR4: 00000000000606e0
  
+ Steps to Reproduce:
  
+ Set kernel.core_pattern sysctl to "|" to disable coredumps.
  
- Steps to Reproduce:
+ $ sudo sysctl kernel.core_pattern="|"
  
  Compile and run following code:
  
  #include <sys/socket.h>
  #include <netinet/in.h>
  #include <string.h>
  
  int main()
  {
-     int listenfd = 0;
-     struct sockaddr_in serv_addr;
+     int listenfd = 0;
+     struct sockaddr_in serv_addr;
  
-     listenfd = socket(AF_INET, SOCK_STREAM, 0);
-     memset(&serv_addr, '0', sizeof(serv_addr));
+     listenfd = socket(AF_INET, SOCK_STREAM, 0);
+     memset(&serv_addr, '0', sizeof(serv_addr));
  
-     serv_addr.sin_family = AF_INET;
-     serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
-     serv_addr.sin_port = htons(6000);
+     serv_addr.sin_family = AF_INET;
+     serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
+     serv_addr.sin_port = htons(6000);
  
-     bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr));
+     bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr));
  
-     listen(listenfd, 10);
+     listen(listenfd, 10);
  
-     *(int*)33 = 33;
+     *(int*)33 = 33;
  
-     return 0;
+     return 0;
  }
  
  Process segfaulted and becomes unkillable, opened socket ports busy.
  
  ProblemType: Bug
  DistroRelease: Ubuntu 19.10
  Package: linux-image-generic 5.3.0.29.33
  ProcVersionSignature: Ubuntu 5.3.0-29.31-generic 5.3.13
  Uname: Linux 5.3.0-29-generic x86_64
  AlsaDevices:
-  total 0
-  crw-rw----+ 1 root audio 116,  1 фев 13 13:24 seq
-  crw-rw----+ 1 root audio 116, 33 фев 13 13:24 timer
+  total 0
+  crw-rw----+ 1 root audio 116,  1 фев 13 13:24 seq
+  crw-rw----+ 1 root audio 116, 33 фев 13 13:24 timer
  AplayDevices: Error: [Errno 2] No such file or directory: 'aplay': 'aplay'
  ApportVersion: 2.20.11-0ubuntu8.2
  Architecture: amd64
  ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord': 
'arecord'
  AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', 
'/dev/snd/timer'] failed with exit code 1:
  CurrentDesktop: KDE
  Date: Thu Feb 13 13:49:19 2020
  IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig': 'iwconfig'
  Lsusb: Error: [Errno 2] No such file or directory: 'lsusb': 'lsusb'
  MachineType: innotek GmbH VirtualBox
  PciMultimedia:
-  
+ 
  ProcFB: 0 svgadrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.3.0-29-generic 
root=UUID=cd3a004e-4e27-4c93-8ae6-e1942680f565 ro mitigations=off 
ipv6.disable=1 net.ifnames=0 video=1280x960
  RelatedPackageVersions:
-  linux-restricted-modules-5.3.0-29-generic N/A
-  linux-backports-modules-5.3.0-29-generic  N/A
-  linux-firmware                            1.183.3
+  linux-restricted-modules-5.3.0-29-generic N/A
+  linux-backports-modules-5.3.0-29-generic  N/A
+  linux-firmware                            1.183.3
  RfKill: Error: [Errno 2] No such file or directory: 'rfkill': 'rfkill'
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  WifiSyslog:
-  
+ 
  dmi.bios.date: 12/01/2006
  dmi.bios.vendor: innotek GmbH
  dmi.bios.version: VirtualBox
  dmi.board.name: VirtualBox
  dmi.board.vendor: Oracle Corporation
  dmi.board.version: 1.2
  dmi.chassis.type: 1
  dmi.chassis.vendor: Oracle Corporation
  dmi.modalias: 
dmi:bvninnotekGmbH:bvrVirtualBox:bd12/01/2006:svninnotekGmbH:pnVirtualBox:pvr1.2:rvnOracleCorporation:rnVirtualBox:rvr1.2:cvnOracleCorporation:ct1:cvr:
  dmi.product.family: Virtual Machine
  dmi.product.name: VirtualBox
  dmi.product.version: 1.2
  dmi.sys.vendor: innotek GmbH

** Tags added: seg

-- 
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/1863086

Title:
  unkillable process (kernel NULL pointer dereference)

Status in linux package in Ubuntu:
  Confirmed
Status in linux source package in Eoan:
  Confirmed
Status in linux source package in Focal:
  Confirmed

Bug description:
  If process that listens socket on any port crashes (segmentation fault) it 
becomes unkillable.
  Kill command does not kill this process.
  Port that listen crashed process never be freed.

  journalctl shows error:

  Feb 13 13:28:09 vbun04 kernel: socktest[1359]: segfault at 21 ip 
000055ec3a6bf11e sp 00007ffd88899fb0 error 6 in socktest[55ec3a6bf000+1000]
  Feb 13 13:28:09 vbun04 kernel: Code: 04 24 02 00 17 70 89 c5 48 b8 30 30 30 
30 30 30 30 30 89 ef 48 89 44 24 08 e8 8e ff ff ff be 0a 00 00 00 89 ef e8 72 
ff ff ff <c7> 04 25 21 00 00 00 21 00 00 00 48 8b 44 24 18
  Feb 13 13:28:09 vbun04 kernel: BUG: kernel NULL pointer dereference, address: 
0000000000000020
  Feb 13 13:28:09 vbun04 kernel: #PF: supervisor read access in kernel mode
  Feb 13 13:28:09 vbun04 kernel: #PF: error_code(0x0000) - not-present page
  Feb 13 13:28:09 vbun04 kernel: PGD 0 P4D 0
  Feb 13 13:28:09 vbun04 kernel: Oops: 0000 [#1] SMP NOPTI
  Feb 13 13:28:09 vbun04 kernel: CPU: 1 PID: 1359 Comm: socktest Tainted: G     
      OE     5.3.0-29-generic #31-Ubuntu
  Feb 13 13:28:09 vbun04 kernel: Hardware name: innotek GmbH 
VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
  Feb 13 13:28:09 vbun04 kernel: RIP: 0010:do_coredump+0x536/0xb30
  Feb 13 13:28:09 vbun04 kernel: Code: 00 48 8b bd 18 ff ff ff 48 85 ff 74 05 
e8 c2 47 fa ff 65 48 8b 04 25 c0 6b 01 00 48 8b 00 48 8b 7d a0 a8 04 0f 85 65 
05 00 00 <48> 8b 57 20 0f b7 02 66 25 00 f0 66 3d 00 80 0f
  Feb 13 13:28:09 vbun04 kernel: RSP: 0000:ffffb464c2c5fca8 EFLAGS: 00010246
  Feb 13 13:28:09 vbun04 kernel: RAX: 0000000000000000 RBX: ffff9d4b76995100 
RCX: 0000000000001afc
  Feb 13 13:28:09 vbun04 kernel: RDX: 0000000000000000 RSI: ffffb464c2c5fc68 
RDI: 0000000000000000
  Feb 13 13:28:09 vbun04 kernel: RBP: ffffb464c2c5fdd8 R08: 0000000000000400 
R09: ffffb464c2c5fbe0
  Feb 13 13:28:09 vbun04 kernel: R10: ffff9d4b75d01170 R11: 0000000000000000 
R12: ffff9d4b7b3df540
  Feb 13 13:28:09 vbun04 kernel: R13: 0000000000000001 R14: 0000000000000000 
R15: ffffffffb9f15920
  Feb 13 13:28:09 vbun04 kernel: FS:  00007f6c91911540(0000) 
GS:ffff9d4b7db00000(0000) knlGS:0000000000000000
  Feb 13 13:28:09 vbun04 kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 
0000000080050033
  Feb 13 13:28:09 vbun04 kernel: CR2: 0000000000000020 CR3: 00000000723ac003 
CR4: 00000000000606e0
  Feb 13 13:28:09 vbun04 kernel: Call Trace:
  Feb 13 13:28:09 vbun04 kernel:  ? wake_up_state+0x10/0x20
  Feb 13 13:28:09 vbun04 kernel:  ? __send_signal+0x1eb/0x3f0
  Feb 13 13:28:09 vbun04 kernel:  get_signal+0x159/0x880
  Feb 13 13:28:09 vbun04 kernel:  do_signal+0x34/0x280
  Feb 13 13:28:09 vbun04 kernel:  ? bad_area+0x47/0x50
  Feb 13 13:28:09 vbun04 kernel:  exit_to_usermode_loop+0xbf/0x160
  Feb 13 13:28:09 vbun04 kernel:  prepare_exit_to_usermode+0x77/0xa0
  Feb 13 13:28:09 vbun04 kernel:  retint_user+0x8/0x8
  Feb 13 13:28:09 vbun04 kernel: RIP: 0033:0x55ec3a6bf11e
  Feb 13 13:28:09 vbun04 kernel: Code: 04 24 02 00 17 70 89 c5 48 b8 30 30 30 
30 30 30 30 30 89 ef 48 89 44 24 08 e8 8e ff ff ff be 0a 00 00 00 89 ef e8 72 
ff ff ff <c7> 04 25 21 00 00 00 21 00 00 00 48 8b 44 24 18
  Feb 13 13:28:09 vbun04 kernel: RSP: 002b:00007ffd88899fb0 EFLAGS: 00010217
  Feb 13 13:28:09 vbun04 kernel: RAX: 0000000000000000 RBX: 0000000000000000 
RCX: 00007f6c918424eb
  Feb 13 13:28:09 vbun04 kernel: RDX: 0000000000000010 RSI: 000000000000000a 
RDI: 0000000000000003
  Feb 13 13:28:09 vbun04 kernel: RBP: 0000000000000003 R08: 0000000000000000 
R09: 00007f6c919331f0
  Feb 13 13:28:09 vbun04 kernel: R10: 0000000000000000 R11: 0000000000000217 
R12: 000055ec3a6bf150
  Feb 13 13:28:09 vbun04 kernel: R13: 00007ffd8889a0b0 R14: 0000000000000000 
R15: 0000000000000000
  Feb 13 13:28:09 vbun04 kernel: Modules linked in: vboxsf(OE) nls_utf8 isofs 
vboxvideo(OE) intel_rapl_msr intel_rapl_common crct10dif_pclmul vmwgfx 
crc32_pclmul ghash_clmulni_intel aesni_intel ttm drm_kms_helper a
  Feb 13 13:28:09 vbun04 kernel: CR2: 0000000000000020
  Feb 13 13:28:09 vbun04 kernel: ---[ end trace 278d665c8727286a ]---
  Feb 13 13:28:09 vbun04 kernel: RIP: 0010:do_coredump+0x536/0xb30
  Feb 13 13:28:09 vbun04 kernel: Code: 00 48 8b bd 18 ff ff ff 48 85 ff 74 05 
e8 c2 47 fa ff 65 48 8b 04 25 c0 6b 01 00 48 8b 00 48 8b 7d a0 a8 04 0f 85 65 
05 00 00 <48> 8b 57 20 0f b7 02 66 25 00 f0 66 3d 00 80 0f
  Feb 13 13:28:09 vbun04 kernel: RSP: 0000:ffffb464c2c5fca8 EFLAGS: 00010246
  Feb 13 13:28:09 vbun04 kernel: RAX: 0000000000000000 RBX: ffff9d4b76995100 
RCX: 0000000000001afc
  Feb 13 13:28:09 vbun04 kernel: RDX: 0000000000000000 RSI: ffffb464c2c5fc68 
RDI: 0000000000000000
  Feb 13 13:28:09 vbun04 kernel: RBP: ffffb464c2c5fdd8 R08: 0000000000000400 
R09: ffffb464c2c5fbe0
  Feb 13 13:28:09 vbun04 kernel: R10: ffff9d4b75d01170 R11: 0000000000000000 
R12: ffff9d4b7b3df540
  Feb 13 13:28:09 vbun04 kernel: R13: 0000000000000001 R14: 0000000000000000 
R15: ffffffffb9f15920
  Feb 13 13:28:09 vbun04 kernel: FS:  00007f6c91911540(0000) 
GS:ffff9d4b7db00000(0000) knlGS:0000000000000000
  Feb 13 13:28:09 vbun04 kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 
0000000080050033
  Feb 13 13:28:09 vbun04 kernel: CR2: 0000000000000020 CR3: 00000000723ac003 
CR4: 00000000000606e0

  Steps to Reproduce:

  Set kernel.core_pattern sysctl to "|" to disable coredumps.

  $ sudo sysctl kernel.core_pattern="|"

  Compile and run following code:

  #include <sys/socket.h>
  #include <netinet/in.h>
  #include <string.h>

  int main()
  {
      int listenfd = 0;
      struct sockaddr_in serv_addr;

      listenfd = socket(AF_INET, SOCK_STREAM, 0);
      memset(&serv_addr, '0', sizeof(serv_addr));

      serv_addr.sin_family = AF_INET;
      serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
      serv_addr.sin_port = htons(6000);

      bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr));

      listen(listenfd, 10);

      *(int*)33 = 33;

      return 0;
  }

  Process segfaulted and becomes unkillable, opened socket ports busy.

  ProblemType: Bug
  DistroRelease: Ubuntu 19.10
  Package: linux-image-generic 5.3.0.29.33
  ProcVersionSignature: Ubuntu 5.3.0-29.31-generic 5.3.13
  Uname: Linux 5.3.0-29-generic x86_64
  AlsaDevices:
   total 0
   crw-rw----+ 1 root audio 116,  1 фев 13 13:24 seq
   crw-rw----+ 1 root audio 116, 33 фев 13 13:24 timer
  AplayDevices: Error: [Errno 2] No such file or directory: 'aplay': 'aplay'
  ApportVersion: 2.20.11-0ubuntu8.2
  Architecture: amd64
  ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord': 
'arecord'
  AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', 
'/dev/snd/timer'] failed with exit code 1:
  CurrentDesktop: KDE
  Date: Thu Feb 13 13:49:19 2020
  IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig': 'iwconfig'
  Lsusb: Error: [Errno 2] No such file or directory: 'lsusb': 'lsusb'
  MachineType: innotek GmbH VirtualBox
  PciMultimedia:

  ProcFB: 0 svgadrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.3.0-29-generic 
root=UUID=cd3a004e-4e27-4c93-8ae6-e1942680f565 ro mitigations=off 
ipv6.disable=1 net.ifnames=0 video=1280x960
  RelatedPackageVersions:
   linux-restricted-modules-5.3.0-29-generic N/A
   linux-backports-modules-5.3.0-29-generic  N/A
   linux-firmware                            1.183.3
  RfKill: Error: [Errno 2] No such file or directory: 'rfkill': 'rfkill'
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  WifiSyslog:

  dmi.bios.date: 12/01/2006
  dmi.bios.vendor: innotek GmbH
  dmi.bios.version: VirtualBox
  dmi.board.name: VirtualBox
  dmi.board.vendor: Oracle Corporation
  dmi.board.version: 1.2
  dmi.chassis.type: 1
  dmi.chassis.vendor: Oracle Corporation
  dmi.modalias: 
dmi:bvninnotekGmbH:bvrVirtualBox:bd12/01/2006:svninnotekGmbH:pnVirtualBox:pvr1.2:rvnOracleCorporation:rnVirtualBox:rvr1.2:cvnOracleCorporation:ct1:cvr:
  dmi.product.family: Virtual Machine
  dmi.product.name: VirtualBox
  dmi.product.version: 1.2
  dmi.sys.vendor: innotek GmbH

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