[Qemu-devel] [Bug 1673957] [NEW] virtfs: mapped-xattr on mount point

[Leo Gaspard]

Public bug reported:

With
  -virtfs local,path="/tmp",security_model=mapped-xattr,mount_tag="shared2"
in the qemu command line,
  shared2 on /mnt/testbis type 9p 
(rw,sync,dirsync,relatime,trans=virtio,version=9p2000.L,msize=262144)
in the guest mount points, and
  tmpfs on /tmp type tmpfs (rw,nosuid,nodev)
in the host mount points (with CONFIG_TMPFS_XATTR=y according to zgrep 
/proc/config.gz), running qemu as user "vm-test", trying to "touch a" in 
/mnt/testbis on the VM fails with "Operation not supported". In addition, no 
file or directory actually present in the host's /tmp can be seen in the 
guest's /mnt/testbis.

When trying to replace "/tmp" with "/tmp/aaa" on the host, with /tmp/aaa
owned by root:root, still running qemu as vm-test, trying to run "ls" in
the guest's /mnt/testbis fails with the weird "ls: reading directory
'.': Cannot allocate memory", while the directory is empty.

After a "chown vm-test /tmp/aaa", the guest can list the files (despite
the permissions already allowing it to do so before), but still not
write new files: "cannot touch 'b': Operation not supported".

Do you have a pointer as to what is happening?

PS: complete setup is running all this inside a qemu VM that I use for
testing, I guess it shouldn't matter but saying it just in case

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1673957

Title:
  virtfs: mapped-xattr on mount point

Status in QEMU:
  New

Bug description:
  With
    -virtfs local,path="/tmp",security_model=mapped-xattr,mount_tag="shared2"
  in the qemu command line,
    shared2 on /mnt/testbis type 9p 
(rw,sync,dirsync,relatime,trans=virtio,version=9p2000.L,msize=262144)
  in the guest mount points, and
    tmpfs on /tmp type tmpfs (rw,nosuid,nodev)
  in the host mount points (with CONFIG_TMPFS_XATTR=y according to zgrep 
/proc/config.gz), running qemu as user "vm-test", trying to "touch a" in 
/mnt/testbis on the VM fails with "Operation not supported". In addition, no 
file or directory actually present in the host's /tmp can be seen in the 
guest's /mnt/testbis.

  When trying to replace "/tmp" with "/tmp/aaa" on the host, with
  /tmp/aaa owned by root:root, still running qemu as vm-test, trying to
  run "ls" in the guest's /mnt/testbis fails with the weird "ls: reading
  directory '.': Cannot allocate memory", while the directory is empty.

  After a "chown vm-test /tmp/aaa", the guest can list the files
  (despite the permissions already allowing it to do so before), but
  still not write new files: "cannot touch 'b': Operation not
  supported".

  Do you have a pointer as to what is happening?

  PS: complete setup is running all this inside a qemu VM that I use for
  testing, I guess it shouldn't matter but saying it just in case

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