Bug 737091

Summary: mount command picks random mount point to operate on during remount
Product: [Fedora] Fedora Reporter: Eric Paris <eparis>
Component: util-linuxAssignee: Karel Zak <kzak>
Status: CLOSED ERRATA QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: 15CC: dwmw2, jonathan, kzak
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Hardware: Unspecified   
OS: Unspecified   
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Fixed In Version: util-linux-2.20.1-1.fc16 Doc Type: Bug Fix
Doc Text:
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Clone Of: Environment:
Last Closed: 2011-10-25 03:45:16 UTC Type: ---
Regression: --- Mount Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description Eric Paris 2011-09-09 15:25:48 UTC
util-linux-2.19.1-1.4.fc15.x86_64

[root@localhost ~]# mount -t tmpfs /mnt/tmp /mnt/tmp
[root@localhost ~]# mkdir /mnt/tmp/rw
[root@localhost ~]# mount -o bind /mnt/tmp/rw /mnt/tmp/rw
[root@localhost ~]# mount -o bind,ro,remount /mnt/tmp/
[root@localhost ~]# cat /proc/self/mountinfo | grep "/mnt/tmp"
66 22 0:56 / /mnt/tmp rw,relatime shared:10 - tmpfs /mnt/tmp rw,rootcontext=system_u:object_r:mnt_t:s0,seclabel
69 66 0:56 /rw /mnt/tmp/rw ro,relatime shared:10 - tmpfs /mnt/tmp rw,rootcontext=system_u:object_r:mnt_t:s0,seclabel

Notice I told it to make /mnt/tmp ro, but instead /mnt/tmp/rw is ro!

strace shows for the bind mount on top of itself:
mount("/mnt/tmp/rw", "/mnt/tmp/rw", 0x7f56abe3d164, MS_MGC_VAL|MS_BIND, NULL) = 0

and it shows for the remount ro:
mount("/mnt/tmp", "/mnt/tmp/rw", 0x7fd660de1164, MS_RDONLY|MS_REMOUNT|MS_RELATIME|MS_BIND, "seclabel") = 0

See how /mnt/tmp/rw magic'd itself up in there?  WTH?

using:
mount -o bind,ro,remount /mnt/tmp /mnt/tmp

results in the right thing.  Why does mount magic up /mnt/tmp/rw?

Comment 1 Karel Zak 2011-09-10 05:16:18 UTC
If (on remount) both <source> and <target> are not specified, then we use

        for (mc = mcprev->prev; mc && mc != mc0; mc = mc->prev)
                if (streq(mc->m.mnt_dir, name) ||
                    streq(mc->m.mnt_fsname, name))
                        return mc;

and that's wrong... we need to scan whole mtab (or mountinfo) for mc->m.mnt_dir and then in another loop for mc->m.mnt_fsname. 

I'll fix it ASAP.

Note that in new (F17?) libmount based mount(8) command will be --target and --source command line options to avoid ambivalent interpretation of the dir|device command line argument.

Comment 2 Karel Zak 2011-09-13 21:02:14 UTC
Fixed by upstream commit 277a6dd53569a409e05316a7bdaed0e78e326762.

Comment 3 Fedora Update System 2011-10-20 11:48:17 UTC
util-linux-2.20.1-1.fc16 has been submitted as an update for Fedora 16.
https://admin.fedoraproject.org/updates/util-linux-2.20.1-1.fc16

Comment 4 Fedora Update System 2011-10-20 22:15:35 UTC
Package util-linux-2.20.1-1.fc16:
* should fix your issue,
* was pushed to the Fedora 16 testing repository,
* should be available at your local mirror within two days.
Update it with:
# su -c 'yum update --enablerepo=updates-testing util-linux-2.20.1-1.fc16'
as soon as you are able to.
Please go to the following url:
https://admin.fedoraproject.org/updates/FEDORA-2011-14685
then log in and leave karma (feedback).

Comment 5 Fedora Update System 2011-10-25 03:45:16 UTC
util-linux-2.20.1-1.fc16 has been pushed to the Fedora 16 stable repository.  If problems still persist, please make note of it in this bug report.