[libvirt] [PATCH 4/6] Remove duplicate entries in lxcBasicMounts array

[Chen Hanxiao]

Reviewed-by: Chen Hanxiao <chenhanxiao at cn.fujitsu.com>

> -----Original Message-----
> From: libvir-list-bounces at redhat.com
[mailto:libvir-list-bounces at redhat.com]
> On Behalf Of Daniel P. Berrange
> Sent: Monday, October 07, 2013 9:07 PM
> To: libvir-list at redhat.com
> Subject: [libvirt] [PATCH 4/6] Remove duplicate entries in lxcBasicMounts
array
> 
> From: "Daniel P. Berrange" <berrange at redhat.com>
> 
> Currently the lxcBasicMounts array has separate entries for
> most mounts, to reflect that we must do a separate mount
> operation to make mounts read-only. Remove the duplicate
> entries and instead set the MS_RDONLY flag against the main
> entry. Then change lxcContainerMountBasicFS to look for the
> MS_RDONLY flag, mask it out & do a separate bind mount.
> 
> Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
> ---
>  src/lxc/lxc_container.c | 44 +++++++++++++++++++++++++++-----------------
>  1 file changed, 27 insertions(+), 17 deletions(-)
> 
> diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
> index 1b1c93b..a7f71ef 100644
> --- a/src/lxc/lxc_container.c
> +++ b/src/lxc/lxc_container.c
> @@ -756,22 +756,12 @@ typedef struct {
>  } virLXCBasicMountInfo;
> 
>  static const virLXCBasicMountInfo lxcBasicMounts[] = {
> -    /* When we want to make a bind mount readonly, for unknown reasons,
> -     * it is currently necessary to bind it once, and then remount the
> -     * bind with the readonly flag. If this is not done, then the
original
> -     * mount point in the main OS becomes readonly too which is not what
> -     * we want. Hence some things have two entries here.
> -     */
>      { "proc", "/proc", "proc", MS_NOSUID|MS_NOEXEC|MS_NODEV },
> -    { "/proc/sys", "/proc/sys", NULL, MS_BIND },
> -    { "/proc/sys", "/proc/sys", NULL,
> MS_BIND|MS_REMOUNT|MS_RDONLY },
> -    { "sysfs", "/sys", "sysfs", MS_NOSUID|MS_NOEXEC|MS_NODEV },
> -    { "sysfs", "/sys", "sysfs", MS_BIND|MS_REMOUNT|MS_RDONLY },
> -    { "securityfs", "/sys/kernel/security", "securityfs",
> MS_NOSUID|MS_NOEXEC|MS_NODEV },
> -    { "securityfs", "/sys/kernel/security", "securityfs",
> MS_BIND|MS_REMOUNT|MS_RDONLY },
> +    { "/proc/sys", "/proc/sys", NULL, MS_BIND|MS_RDONLY },
> +    { "sysfs", "/sys", "sysfs",
> MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY },
> +    { "securityfs", "/sys/kernel/security", "securityfs",
> MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY },
>  #if WITH_SELINUX
> -    { SELINUX_MOUNT, SELINUX_MOUNT, "selinuxfs",
> MS_NOSUID|MS_NOEXEC|MS_NODEV },
> -    { SELINUX_MOUNT, SELINUX_MOUNT, NULL,
> MS_BIND|MS_REMOUNT|MS_RDONLY },
> +    { SELINUX_MOUNT, SELINUX_MOUNT, "selinuxfs",
> MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY },
>  #endif
>  };
> 
> @@ -852,6 +842,7 @@ static int lxcContainerMountBasicFS(bool
> userns_enabled)
>      VIR_DEBUG("Mounting basic filesystems");
> 
>      for (i = 0; i < ARRAY_CARDINALITY(lxcBasicMounts); i++) {
> +        bool bindOverReadonly;
>          virLXCBasicMountInfo const *mnt = &lxcBasicMounts[i];
> 
>          VIR_DEBUG("Processing %s -> %s",
> @@ -878,13 +869,32 @@ static int lxcContainerMountBasicFS(bool
> userns_enabled)
>              goto cleanup;
>          }
> 
> +        /*
> +         * We can't immediately set the MS_RDONLY flag when mounting
> filesystems
> +         * because (in at least some kernel versions) this will propagate
> back
> +         * to the original mount in the host OS, turning it readonly too.
This
> +         * We mount the filesystem in read-write mode initially, and then
do
> a
> +         * separate read-only bind mount on top of that.
> +         */
> +        bindOverReadonly = !!(mnt->mflags & MS_RDONLY);
> +
>          VIR_DEBUG("Mount %s on %s type=%s flags=%x",
> -                  mnt->src, mnt->dst, mnt->type, mnt->mflags);
> -        if (mount(mnt->src, mnt->dst, mnt->type, mnt->mflags, NULL) < 0)
{
> +                  mnt->src, mnt->dst, mnt->type, mnt->mflags &
> ~MS_RDONLY);
> +        if (mount(mnt->src, mnt->dst, mnt->type, mnt->mflags &
> ~MS_RDONLY, NULL) < 0) {
>              virReportSystemError(errno,
>                                   _("Failed to mount %s on %s type %s
> flags=%x"),
>                                   mnt->src, mnt->dst,
> NULLSTR(mnt->type),
> -                                 mnt->mflags);
> +                                 mnt->mflags & ~MS_RDONLY);
> +            goto cleanup;
> +        }
> +
> +        if (bindOverReadonly &&
> +            mount(mnt->src, mnt->dst, NULL,
> +                  MS_BIND|MS_REMOUNT|MS_RDONLY, NULL) < 0) {
> +            virReportSystemError(errno,
> +                                 _("Failed to re-mount %s on %s
> flags=%x"),
> +                                 mnt->src, mnt->dst,
> +
> MS_BIND|MS_REMOUNT|MS_RDONLY);
>              goto cleanup;
>          }
>      }
> --
> 1.8.3.1
> 
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