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filesystem_limit/snapshot_limit is incorrectly enforced against root

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The filesystem_limit and snapshot_limit properties limit the number of
filesystems or snapshots that can be created below this dataset.
According to the manpage, "The limit is not enforced if the user is
allowed to change the limit."  Two types of users are allowed to change
the limit:

1. Those that have been delegated the `filesystem_limit` or
`snapshot_limit` permission, e.g. with
`zfs allow USER filesystem_limit DATASET`.  This works properly.

2. A user with elevated system privileges (e.g. root).  This does not
work - the root user will incorrectly get an error when trying to create
a snapshot/filesystem, if it exceeds the `_limit` property.

The problem is that `priv_policy_ns()` does not work if the `cred_t` is
not that of the current process.  This happens when
`dsl_enforce_ds_ss_limits()` is called in syncing context (as part of a
sync task's check func) to determine the permissions of the
corresponding user process.

This commit fixes the issue by passing the `task_struct` (typedef'ed as
a `proc_t`) to syncing context, and then using `has_capability()` to
determine if that process is privileged.  Note that we still need to
pass the `cred_t` to syncing context so that we can check if the user
was delegated this permission with `zfs allow`.

This problem only impacts Linux.  Wrappers are added to FreeBSD but it
continues to use `priv_check_cred()`, which works on arbitrary `cred_t`.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes #8226
Closes #10545
This commit is contained in:
Matthew Ahrens
2020-07-11 17:18:02 -07:00
committed by GitHub
parent 217f48373f
commit e59a377a8f
17 changed files with 104 additions and 48 deletions
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include/os/freebsd/spl/sys/policy.h
+1
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@@ -37,6 +37,7 @@ struct vattr;
int secpolicy_nfs(cred_t *cr);
int secpolicy_zfs(cred_t *crd);
int secpolicy_zfs_proc(cred_t *cr, proc_t *proc);
int secpolicy_sys_config(cred_t *cr, int checkonly);
int secpolicy_zinject(cred_t *cr);
int secpolicy_fs_unmount(cred_t *cr, struct mount *vfsp);
include/os/linux/zfs/sys/policy.h
+1
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@@ -48,6 +48,7 @@ int secpolicy_vnode_setid_retain(const cred_t *, boolean_t);
int secpolicy_vnode_setids_setgids(const cred_t *, gid_t);
int secpolicy_zinject(const cred_t *);
int secpolicy_zfs(const cred_t *);
int secpolicy_zfs_proc(const cred_t *, proc_t *);
void secpolicy_setid_clear(vattr_t *, cred_t *);
int secpolicy_setid_setsticky_clear(struct inode *, vattr_t *,
const vattr_t *, cred_t *);