On Tue, Jan 10, 2017 at 02:26:48PM +0300, Konstantin Khlebnikov wrote:
> If overlay was mounted by root then quota set for upper layer does not work
> because overlay now always use mounter's credentials for operations.
>
Hi Konstantin,
So CAP_SYS_RESOURCE bypasses the quota checks?
I just created dir upper on xfs filesystem and defined quota of 1G and
as root user (with cap_sys_resoureces), I am not able to create file
bigger than 1g in that dir. So looks like xfs quota took affect even
for privileged user with CAP_SYS_RESOURCE set.
What am I missing?
Vivek
> This patch adds second copy of credentials without CAP_SYS_RESOURCE and
> use it if current task doesn't have this capability in mounter's user-ns.
> This affects creation new files, whiteouts, and copy-up operations.
>
> Now quota limits are ignored only if both mounter and current task have
> capability CAP_SYS_RESOURCE in root user namespace.
>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> Fixes: 1175b6b8d963 ("ovl: do operations on underlying file system in mounter's context")
> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> Cc: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> ---
> fs/overlayfs/ovl_entry.h | 2 ++
> fs/overlayfs/super.c | 13 ++++++++++++-
> fs/overlayfs/util.c | 10 +++++++++-
> 3 files changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index d14bca1850d9..55eb3b08e292 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -27,6 +27,8 @@ struct ovl_fs {
> struct ovl_config config;
> /* creds of process who forced instantiation of super block */
> const struct cred *creator_cred;
> + /* the same credentials without CAP_SYS_RESOURCE */
> + const struct cred *creator_cred_unpriv;
> };
>
> /* private information held for every overlayfs dentry */
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 20f48abbb82f..6a15693641e0 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -157,6 +157,7 @@ static void ovl_put_super(struct super_block *sb)
> kfree(ufs->config.upperdir);
> kfree(ufs->config.workdir);
> put_cred(ufs->creator_cred);
> + put_cred(ufs->creator_cred_unpriv);
> kfree(ufs);
> }
>
> @@ -701,6 +702,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
> unsigned int stacklen = 0;
> unsigned int i;
> bool remote = false;
> + struct cred *cred;
> int err;
>
> err = -ENOMEM;
> @@ -874,10 +876,17 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
> if (!ufs->creator_cred)
> goto out_put_lower_mnt;
>
> + cred = prepare_creds();
> + if (!cred)
> + goto out_put_cred;
> +
> + ufs->creator_cred_unpriv = cred;
> + cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);
> +
> err = -ENOMEM;
> oe = ovl_alloc_entry(numlower);
> if (!oe)
> - goto out_put_cred;
> + goto out_put_cred_unpriv;
>
> sb->s_magic = OVERLAYFS_SUPER_MAGIC;
> sb->s_op = &ovl_super_operations;
> @@ -914,6 +923,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
>
> out_free_oe:
> kfree(oe);
> +out_put_cred_unpriv:
> + put_cred(ufs->creator_cred_unpriv);
> out_put_cred:
> put_cred(ufs->creator_cred);
> out_put_lower_mnt:
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index 952286f4826c..92f60096c5da 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -35,8 +35,16 @@ struct dentry *ovl_workdir(struct dentry *dentry)
> const struct cred *ovl_override_creds(struct super_block *sb)
> {
> struct ovl_fs *ofs = sb->s_fs_info;
> + const struct cred *cred = ofs->creator_cred;
>
> - return override_creds(ofs->creator_cred);
> + /*
> + * Do not override quota inode limit if current task is not
> + * capable to do that in mounter's user namespace.
> + */
> + if (!ns_capable_noaudit(cred->user_ns, CAP_SYS_RESOURCE))
> + cred = ofs->creator_cred_unpriv;
> +
> + return override_creds(cred);
> }
>
> struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
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