[Devel] [PATCH hci-8.1 0/2] Fix kernel crash in overlayfs

[Vladimir Riabchun]

When testing CRIU with containers with docker images,
we found an easily reproducible kernel crash:

[ 2300.870181] BUG: kernel NULL pointer dereference, address: 0000000000000005
[ 2300.871537] #PF: supervisor read access in kernel mode
[ 2300.872577] #PF: error_code(0x0000) - not-present page
[ 2300.873595] PGD 800000010a18f067 P4D 800000010a18f067 PUD 10730c067 PMD 0 
[ 2300.874900] Oops: Oops: 0000 [#1] SMP PTI
[ 2300.875742] CPU: 1 UID: 0 PID: 5419 Comm: criu ve: 0 Kdump: loaded Not tainted 6.12.0-211.39.1.16.6.vz10.x86_64 #1 16.6 PREEMPT(voluntary) 
[ 2300.878057] Hardware name: Acronis OpenStack Compute/Virtuozzo, BIOS 1.16.1-1.vz9.2 04/01/2014
[ 2300.879684] RIP: 0010:ovl_get_index_name_fh+0x18/0x70 [overlay]
[ 2300.880859] Code: ...
[ 2300.884128] RSP: 0018:ffffd32582e0f7c0 EFLAGS: 00010246
[ 2300.895807] Call Trace:
[ 2300.896397]  <TASK>
[ 2300.904435]  ovl_create_index+0x82/0x260 [overlay]
[ 2300.905406]  ovl_copy_up_workdir+0x30a/0x330 [overlay]
[ 2300.906427]  ovl_do_copy_up+0x10d/0x2e0 [overlay]
[ 2300.907387]  ovl_copy_up_one+0x456/0x720 [overlay]
[ 2300.910736]  ovl_copy_up_flags+0x81/0x110 [overlay]
[ 2300.911740]  ovl_create_object+0x51/0x130 [overlay]
[ 2300.912719]  vfs_mkdir+0x194/0x250
[ 2300.913470]  do_mkdirat+0x14c/0x180
[ 2300.914223]  __x64_sys_mkdir+0x46/0x70
[ 2300.915019]  do_syscall_64+0x7d/0x160
[ 2300.922814]  entry_SYSCALL_64_after_hwframe+0x76/0x7e

The cause is that overlayfs does some feature checks on superblock
creation using capable/ve_capable and it stores current credentials.
But ve_capable check result depends on both current creds and
current VE. Later, overlayfs switches credentials only, leading
to unexpected feature disappearance.

https://virtuozzo.atlassian.net/browse/VSTOR-143259 - non-CRIU repro
https://virtuozzo.atlassian.net/browse/VSTOR-142405

Signed-off-by: Vladimir Riabchun <vladimir.riabchun at virtuozzo.com>
---
Vladimir Riabchun (2):
      capability: Add new helper to check specific VE capabilities
      ovl: Keep creator VE in overlayfs superblock

 fs/overlayfs/copy_up.c     |  2 +-
 fs/overlayfs/namei.c       |  2 +-
 fs/overlayfs/overlayfs.h   |  2 +-
 fs/overlayfs/ovl_entry.h   |  1 +
 fs/overlayfs/params.c      |  3 +++
 fs/overlayfs/super.c       |  7 +++++--
 fs/overlayfs/util.c        |  4 ++--
 include/linux/capability.h |  3 +++
 kernel/capability.c        | 15 +++++++++++++--
 9 files changed, 30 insertions(+), 9 deletions(-)
---
base-commit: 3851feefb321d7dee9e57cbe7926410aa6dd043f
change-id: 20260918-ovl-use-orig-ve-2dc365976202

Best regards,
--  
Vladimir Riabchun <vladimir.riabchun at virtuozzo.com>