Unable to delete files to trash in a bind-mounted filesystem

bindmounttrash

I'm trying to set up shared home directory for two Linux installations and thus I'm using bind-mounts. My user is named dbz and his home directory is /home/dbz. I also have shared directory /home/shared where I store my shared files (this folder is also owned by user dbz).

I mount another directories from this shared directory into my home directory using binding:

mount -B /home/shared/work /home/dbz/work

This solution solves my needs and the only issue I have and don't know how to resolve is – when I'm trying to delete a file or directory from mounted directory I cannot delete it to trash, only permanent deletion is possible.
For example:

deleting file /home/shared/work/test.txt: OK, because deleting right from the directory where the file test.txt resides;
deleting file /home/dbz/work/test.txt: CAN'T, because… by the way, because what? do bind-mounts have some restrictions on file deletion?

Finally an issue submitted to bugzilla.kernel.org

Best Answer

This is a linux kernel issue. It's not looking at the true super-block of the source and destination filesystems:

17926 rename("d1/foo", "d2/foo")        = -1 EXDEV (Invalid cross-device link)

Looks like the issue is in do_rename() (fs/namei.c):

    error = -EXDEV;
    if (oldnd.mnt != newnd.mnt)
            goto exit2;

*sigh*

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Mount and Hardlink – Why Can’t Create Hardlink from a Bind Mount Directory?

There's a disappointing lack of comments in the code. It's as if no-one ever thought it useful, since the time bind mounts were implemented in v2.4. Surely all you'd need to do is substitute .mnt->mnt_sb where it says .mnt...

Because it gives you a security boundary around a subtree.

PS: that had been discussed quite a few times, but to avoid searches: consider e.g. mount --bind /tmp /tmp; now you've got a situation when users can't create links to elsewhere no root fs, even though they have /tmp writable to them. Similar technics works for other isolation needs - basically, you can confine rename/link to given subtree. IOW, it's a deliberate feature. Note that you can bind a bunch of trees into chroot and get predictable restrictions regardless of how the stuff might get rearranged a year later in the main tree, etc.

-- Al Viro

There's a concrete example further down the thread

Whenever we get mount -r --bind working properly (which I use to place copies of necessary shared libraries inside chroot jails while allowing page cache sharing), this feature would break security.
mkdir /usr/lib/libs.jail
for i in $LIST_OF_LIBRARIES; do
ln /usr/lib/$i /usr/lib/libs.jail/$i
done
mount -r /usr/lib/libs.jail /jail/lib
chown prisoner /usr/log/jail
mount /usr/log/jail /jail/usr/log
chrootuid /jail prisoner /bin/untrusted &
Although protections should be enough, but I'd rather avoid having the prisoner link /jail/lib/libfoo.so (write returns EROFS) to /jail/usr/log where it's potentially writeable.

Pcmanfm doesn’t send files to trash on external drive

This is a bit late, but I ran into the same issue. As it turns out, you have to disable the 'Erase files on removable media instead of "trash can" creation' preference. Apparently PCManFM sees any drives with an unmount button as removable media. Once that's done, sending files to trash works as expected.

Best Answer

Related Solutions

Mount and Hardlink – Why Can’t Create Hardlink from a Bind Mount Directory?

Pcmanfm doesn’t send files to trash on external drive

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