On 10.01.2017 19:06, Vivek Goyal wrote:
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?
Yep. See in fs/quota/dquot.c
static int ignore_hardlimit(struct dquot *dquot)
{
struct mem_dqinfo *info = &sb_dqopt(dquot->dq_sb)->info[dquot->dq_id.type];
return capable(CAP_SYS_RESOURCE) &&
(info->dqi_format->qf_fmt_id != QFMT_VFS_OLD ||
!(info->dqi_flags & DQF_ROOT_SQUASH));
}
Feature DQF_ROOT_SQUASH which disables this bypassing is obsoleted in modern quota formats.
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?
XFS has its own quota and I cannot find any capable(CAP_SYS_RESOURCE) here.
So, probably XFS ignores this capability and always limits root user.
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)
--
Konstantin
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
