Comment 0 for bug 1824981

Ubuntu 18.04.2 LTS
Linux SRV013 4.15.0-47-generic #50-Ubuntu SMP Wed Mar 13 10:44:52 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

DELL R740, 2 CPU (40 Cores, 80 Threads), 384 GiB RAM

top - 12:39:53 up 3:41, 4 users, load average: 66.19, 64.06, 76.90
Tasks: 1076 total, 1 running, 675 sleeping, 12 stopped, 1 zombie
%Cpu(s): 28.2 us, 0.3 sy, 0.0 ni, 71.5 id, 0.0 wa, 0.0 hi, 0.1 si, 0.0 st
KiB Mem : 39483801+total, 24077185+free, 57428284 used, 96637872 buff/cache
KiB Swap: 999420 total, 999420 free, 0 used. 33477683+avail Mem

We've seen the following bug many times since we introduced new machines running Ubuntu 18. Wasn't an issue older machines running Ubuntu 16. Three different machines are affected, so it's rather not a hardware issue.

| detected buffer overflow in strcat
| ------------[ cut here ]------------
| kernel BUG at /build/linux-6ZmFRN/linux-4.15.0/lib/string.c:1052!
| invalid opcode: 0000 [#1] SMP PTI
| Modules linked in: [...]
| Hardware name: Dell Inc. PowerEdge R740/0923K0, BIOS 1.6.11 11/20/2018
| RIP: 0010:fortify_panic+0x13/0x22
| [...]
| Call Trace:
| smb21_set_oplock_level+0x147/0x1a0 [cifs]
| smb3_set_oplock_level+0x22/0x90 [cifs]
| smb2_set_fid+0x76/0xb0 [cifs]
| cifs_new_fileinfo+0x259/0x390 [cifs]
| ? smb2_get_lease_key+0x40/0x40 [cifs]
| ? cifs_new_fileinfo+0x259/0x390 [cifs]
| cifs_open+0x3db/0x8d0 [cifs]
| [...]

(Full dmesg output attached)

After hitting this bug there are many cifs related dmesg entries, processes lock up and eventually the systems freezes.

The share is mounted using:
//server/share /mnt/server/ cifs defaults,auto,iocharset=utf8,noperm,file_mode=0777,dir_mode=0777,credentials=/root/passwords/share,domain=myDomain,uid=myUser,gid=10513,mfsymlinks

Currently we're testing the cifs mount options "cache=none" as the bug seems to be oplock related.