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Re: [libvirt] QEMU fstatfs(2) and libvirt SELinux policy



On Fri, Mar 09, 2012 at 11:32:47AM +0000, Stefan Hajnoczi wrote:
> Hi,
> I have a question about the libvirt SELinux policy that can be applied
> to QEMU processes.  Yesterday Laine helped Khoa and me diagnose an
> issue where QEMU was doing fstatfs(2) but SELinux prevented this
> FILESYSTEM__GETATTR operation, resulting in a failed syscall with
> -EACCES.  The SELinux hook is:
> 
> security/selinux/hooks.c:selinux_sb_statfs():
>         return superblock_has_perm(cred, dentry->d_sb,
> FILESYSTEM__GETATTR, &ad);
> 
> It turns out this problem also affects XFS discard support in QEMU
> today.  QEMU calls platform_test_xfs_fd() in libxfs, which works like
> this:
> 
> static __inline__ int platform_test_xfs_fd(int fd)
> {
>         struct statfs buf;
>         if (fstatfs(fd, &buf) < 0)
>                 return 0;
>         return (buf.f_type == 0x58465342);      /* XFSB */
> }
> 
> In other words, XFS detection will fail when SELinux is enabled.
> 
> I'm not familiar with libvirt's use of SELinux.  Can someone explain
> if we need to expand the policy in libvirt and how to do that?

Just file a BZ against 'selinux-policy' in Fedora and provide the AVC
record from /var/log/audit/audit.log and a note explaining why we
should allow this. Dan Walsh will quickly update the policy to comply


Daniel
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