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Bug 1815534 - mount --rbind -o rprivate doesn't do recursive bind mount
Summary: mount --rbind -o rprivate doesn't do recursive bind mount
Keywords:
Status: CLOSED NEXTRELEASE
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: util-linux
Version: 7.8
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: Karel Zak
QA Contact: Radka Brychtova
URL:
Whiteboard:
Depends On:
Blocks: 1946921
TreeView+ depends on / blocked
 
Reported: 2020-03-20 14:09 UTC by Pavel Raiskup
Modified: 2021-04-07 09:03 UTC (History)
2 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
: 1946921 (view as bug list)
Environment:
Last Closed: 2020-03-23 11:10:27 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)
reproducer (889 bytes, application/x-shellscript)
2020-03-20 14:09 UTC, Pavel Raiskup 		no flags Details
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Description Pavel Raiskup 2020-03-20 14:09:09 UTC 
Created attachment 1671921 [details]
reproducer

This bug may be used for documentation purposes only, and closed, if you wish.
It originally caused bug in mock, so we resolved it in mock PR [1].

When you do
   $ mount --rbind -o rprivate root bootstrap_root/root
.. only the top-most mount from ./root is bind-mounted to
bootstrap_root/root, not the sub-mounts like ./root/sub-mount.

This works fine on Fedora box.

Try the attached reproducer:
  # bash ./reproducer
  ...
  # findmnt --raw | cut -d' ' -f1 | grep /tmp/
  /tmp/root
  /tmp/bootstrap_root
  /tmp/root/cache_submount
  /tmp/bootstrap_root/root

It means that /tmp/bootstrap_root/root/cache_submount is missing.

[1] https://github.com/rpm-software-management/mock/pull/536
Comment 2 Karel Zak 2020-03-23 11:10:27 UTC 
Sounds like bug #1584443. Unfortunately, not fixed on RHEL-7 (but fixed in RHEL>=8).

The best workaround is to split the "mount --rbind -o rprivate" command into two separate mount commands to be compatible with old versions.

Upstream commites:
 4ebea84bb1ca6b0fa817588aba13de26c8d5e5a0
 816773b475900909d42c2c8282a6ac50252cac22
 6691d53797ccc2e5ac840c5b1680fceaa23122db
 
Not sure if we really need it in RHEL-7 as it's a chance to relatively sensitive stuff and no reported by customers. 

Closing. Please, reopen if really need it. Thanks!
Comment 3 David Ward 2021-04-03 17:45:12 UTC 
@Karel: no this is not fixed in RHEL 8, which also has util-linux 2.32.1 without a patch for this.
Comment 4 Karel Zak 2021-04-07 09:00:48 UTC 
(In reply to David Ward from comment #3)
> @Karel: no this is not fixed in RHEL 8, which also has util-linux 2.32.1
> without a patch for this.

Ah, now I see what do you mean (for RHEL-8) 

The problem is not the feature itself, but the flag MS_REC which is not applied to
the first mount(2) call. It was originally reported for Fedora (bug #1584443) and 
fixed by upstream commit 816773b475900909d42c2c8282a6ac50252cac22.

# strace -e mount mount --rbind -o rprivate /mnt/test /mnt/test
mount("/mnt/test", "/mnt/test", 0x5607fc749960, MS_MGC_VAL|MS_BIND, NULL) = 0
mount("none", "/mnt/test", NULL, MS_REC|MS_PRIVATE, NULL) = 0

the same on Fedora:

# strace -e mount mount --rbind -o rprivate /mnt/test /mnt/test
mount("/mnt/test", "/mnt/test", 0x55c2efb1ec80, MS_BIND|MS_REC, NULL) = 0
mount("none", "/mnt/test", NULL, MS_REC|MS_PRIVATE, NULL) = 0


For RHEL-7 it's really too invasive (as there is missing all the code), but for RHEL-8
it's something we can fix in the 8.5 -- I'll clone this issue. 

Thanks for your patience ;-)
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