644473e9c6
Pull user namespace enhancements from Eric Biederman:
"This is a course correction for the user namespace, so that we can
reach an inexpensive, maintainable, and reasonably complete
implementation.
Highlights:
- Config guards make it impossible to enable the user namespace and
code that has not been converted to be user namespace safe.
- Use of the new kuid_t type ensures the if you somehow get past the
config guards the kernel will encounter type errors if you enable
user namespaces and attempt to compile in code whose permission
checks have not been updated to be user namespace safe.
- All uids from child user namespaces are mapped into the initial
user namespace before they are processed. Removing the need to add
an additional check to see if the user namespace of the compared
uids remains the same.
- With the user namespaces compiled out the performance is as good or
better than it is today.
- For most operations absolutely nothing changes performance or
operationally with the user namespace enabled.
- The worst case performance I could come up with was timing 1
billion cache cold stat operations with the user namespace code
enabled. This went from 156s to 164s on my laptop (or 156ns to
164ns per stat operation).
- (uid_t)-1 and (gid_t)-1 are reserved as an internal error value.
Most uid/gid setting system calls treat these value specially
anyway so attempting to use -1 as a uid would likely cause
entertaining failures in userspace.
- If setuid is called with a uid that can not be mapped setuid fails.
I have looked at sendmail, login, ssh and every other program I
could think of that would call setuid and they all check for and
handle the case where setuid fails.
- If stat or a similar system call is called from a context in which
we can not map a uid we lie and return overflowuid. The LFS
experience suggests not lying and returning an error code might be
better, but the historical precedent with uids is different and I
can not think of anything that would break by lying about a uid we
can't map.
- Capabilities are localized to the current user namespace making it
safe to give the initial user in a user namespace all capabilities.
My git tree covers all of the modifications needed to convert the core
kernel and enough changes to make a system bootable to runlevel 1."
Fix up trivial conflicts due to nearby independent changes in fs/stat.c
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: (46 commits)
userns: Silence silly gcc warning.
cred: use correct cred accessor with regards to rcu read lock
userns: Convert the move_pages, and migrate_pages permission checks to use uid_eq
userns: Convert cgroup permission checks to use uid_eq
userns: Convert tmpfs to use kuid and kgid where appropriate
userns: Convert sysfs to use kgid/kuid where appropriate
userns: Convert sysctl permission checks to use kuid and kgids.
userns: Convert proc to use kuid/kgid where appropriate
userns: Convert ext4 to user kuid/kgid where appropriate
userns: Convert ext3 to use kuid/kgid where appropriate
userns: Convert ext2 to use kuid/kgid where appropriate.
userns: Convert devpts to use kuid/kgid where appropriate
userns: Convert binary formats to use kuid/kgid where appropriate
userns: Add negative depends on entries to avoid building code that is userns unsafe
userns: signal remove unnecessary map_cred_ns
userns: Teach inode_capable to understand inodes whose uids map to other namespaces.
userns: Fail exec for suid and sgid binaries with ids outside our user namespace.
userns: Convert stat to return values mapped from kuids and kgids
userns: Convert user specfied uids and gids in chown into kuids and kgid
userns: Use uid_eq gid_eq helpers when comparing kuids and kgids in the vfs
...
117 lines
3 KiB
C
117 lines
3 KiB
C
/* Key permission checking
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*
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* Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/module.h>
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#include <linux/security.h>
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#include "internal.h"
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/**
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* key_task_permission - Check a key can be used
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* @key_ref: The key to check.
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* @cred: The credentials to use.
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* @perm: The permissions to check for.
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*
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* Check to see whether permission is granted to use a key in the desired way,
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* but permit the security modules to override.
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*
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* The caller must hold either a ref on cred or must hold the RCU readlock.
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*
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* Returns 0 if successful, -EACCES if access is denied based on the
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* permissions bits or the LSM check.
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*/
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int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
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key_perm_t perm)
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{
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struct key *key;
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key_perm_t kperm;
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int ret;
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key = key_ref_to_ptr(key_ref);
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if (key->user->user_ns != cred->user_ns)
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goto use_other_perms;
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/* use the second 8-bits of permissions for keys the caller owns */
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if (key->uid == cred->fsuid) {
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kperm = key->perm >> 16;
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goto use_these_perms;
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}
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/* use the third 8-bits of permissions for keys the caller has a group
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* membership in common with */
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if (key->gid != -1 && key->perm & KEY_GRP_ALL) {
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if (key->gid == cred->fsgid) {
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kperm = key->perm >> 8;
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goto use_these_perms;
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}
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ret = groups_search(cred->group_info,
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make_kgid(current_user_ns(), key->gid));
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if (ret) {
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kperm = key->perm >> 8;
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goto use_these_perms;
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}
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}
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use_other_perms:
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/* otherwise use the least-significant 8-bits */
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kperm = key->perm;
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use_these_perms:
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/* use the top 8-bits of permissions for keys the caller possesses
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* - possessor permissions are additive with other permissions
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*/
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if (is_key_possessed(key_ref))
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kperm |= key->perm >> 24;
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kperm = kperm & perm & KEY_ALL;
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if (kperm != perm)
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return -EACCES;
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/* let LSM be the final arbiter */
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return security_key_permission(key_ref, cred, perm);
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}
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EXPORT_SYMBOL(key_task_permission);
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/**
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* key_validate - Validate a key.
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* @key: The key to be validated.
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*
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* Check that a key is valid, returning 0 if the key is okay, -ENOKEY if the
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* key is invalidated, -EKEYREVOKED if the key's type has been removed or if
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* the key has been revoked or -EKEYEXPIRED if the key has expired.
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*/
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int key_validate(const struct key *key)
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{
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unsigned long flags = key->flags;
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if (flags & (1 << KEY_FLAG_INVALIDATED))
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return -ENOKEY;
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/* check it's still accessible */
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if (flags & ((1 << KEY_FLAG_REVOKED) |
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(1 << KEY_FLAG_DEAD)))
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return -EKEYREVOKED;
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/* check it hasn't expired */
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if (key->expiry) {
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struct timespec now = current_kernel_time();
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if (now.tv_sec >= key->expiry)
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return -EKEYEXPIRED;
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}
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return 0;
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}
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EXPORT_SYMBOL(key_validate);
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