a6f76f23d2
Make execve() take advantage of copy-on-write credentials, allowing it to set
up the credentials in advance, and then commit the whole lot after the point
of no return.
This patch and the preceding patches have been tested with the LTP SELinux
testsuite.
This patch makes several logical sets of alteration:
(1) execve().
The credential bits from struct linux_binprm are, for the most part,
replaced with a single credentials pointer (bprm->cred). This means that
all the creds can be calculated in advance and then applied at the point
of no return with no possibility of failure.
I would like to replace bprm->cap_effective with:
cap_isclear(bprm->cap_effective)
but this seems impossible due to special behaviour for processes of pid 1
(they always retain their parent's capability masks where normally they'd
be changed - see cap_bprm_set_creds()).
The following sequence of events now happens:
(a) At the start of do_execve, the current task's cred_exec_mutex is
locked to prevent PTRACE_ATTACH from obsoleting the calculation of
creds that we make.
(a) prepare_exec_creds() is then called to make a copy of the current
task's credentials and prepare it. This copy is then assigned to
bprm->cred.
This renders security_bprm_alloc() and security_bprm_free()
unnecessary, and so they've been removed.
(b) The determination of unsafe execution is now performed immediately
after (a) rather than later on in the code. The result is stored in
bprm->unsafe for future reference.
(c) prepare_binprm() is called, possibly multiple times.
(i) This applies the result of set[ug]id binaries to the new creds
attached to bprm->cred. Personality bit clearance is recorded,
but now deferred on the basis that the exec procedure may yet
fail.
(ii) This then calls the new security_bprm_set_creds(). This should
calculate the new LSM and capability credentials into *bprm->cred.
This folds together security_bprm_set() and parts of
security_bprm_apply_creds() (these two have been removed).
Anything that might fail must be done at this point.
(iii) bprm->cred_prepared is set to 1.
bprm->cred_prepared is 0 on the first pass of the security
calculations, and 1 on all subsequent passes. This allows SELinux
in (ii) to base its calculations only on the initial script and
not on the interpreter.
(d) flush_old_exec() is called to commit the task to execution. This
performs the following steps with regard to credentials:
(i) Clear pdeath_signal and set dumpable on certain circumstances that
may not be covered by commit_creds().
(ii) Clear any bits in current->personality that were deferred from
(c.i).
(e) install_exec_creds() [compute_creds() as was] is called to install the
new credentials. This performs the following steps with regard to
credentials:
(i) Calls security_bprm_committing_creds() to apply any security
requirements, such as flushing unauthorised files in SELinux, that
must be done before the credentials are changed.
This is made up of bits of security_bprm_apply_creds() and
security_bprm_post_apply_creds(), both of which have been removed.
This function is not allowed to fail; anything that might fail
must have been done in (c.ii).
(ii) Calls commit_creds() to apply the new credentials in a single
assignment (more or less). Possibly pdeath_signal and dumpable
should be part of struct creds.
(iii) Unlocks the task's cred_replace_mutex, thus allowing
PTRACE_ATTACH to take place.
(iv) Clears The bprm->cred pointer as the credentials it was holding
are now immutable.
(v) Calls security_bprm_committed_creds() to apply any security
alterations that must be done after the creds have been changed.
SELinux uses this to flush signals and signal handlers.
(f) If an error occurs before (d.i), bprm_free() will call abort_creds()
to destroy the proposed new credentials and will then unlock
cred_replace_mutex. No changes to the credentials will have been
made.
(2) LSM interface.
A number of functions have been changed, added or removed:
(*) security_bprm_alloc(), ->bprm_alloc_security()
(*) security_bprm_free(), ->bprm_free_security()
Removed in favour of preparing new credentials and modifying those.
(*) security_bprm_apply_creds(), ->bprm_apply_creds()
(*) security_bprm_post_apply_creds(), ->bprm_post_apply_creds()
Removed; split between security_bprm_set_creds(),
security_bprm_committing_creds() and security_bprm_committed_creds().
(*) security_bprm_set(), ->bprm_set_security()
Removed; folded into security_bprm_set_creds().
(*) security_bprm_set_creds(), ->bprm_set_creds()
New. The new credentials in bprm->creds should be checked and set up
as appropriate. bprm->cred_prepared is 0 on the first call, 1 on the
second and subsequent calls.
(*) security_bprm_committing_creds(), ->bprm_committing_creds()
(*) security_bprm_committed_creds(), ->bprm_committed_creds()
New. Apply the security effects of the new credentials. This
includes closing unauthorised files in SELinux. This function may not
fail. When the former is called, the creds haven't yet been applied
to the process; when the latter is called, they have.
The former may access bprm->cred, the latter may not.
(3) SELinux.
SELinux has a number of changes, in addition to those to support the LSM
interface changes mentioned above:
(a) The bprm_security_struct struct has been removed in favour of using
the credentials-under-construction approach.
(c) flush_unauthorized_files() now takes a cred pointer and passes it on
to inode_has_perm(), file_has_perm() and dentry_open().
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
122 lines
3.4 KiB
C
122 lines
3.4 KiB
C
/*
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* NSA Security-Enhanced Linux (SELinux) security module
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*
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* This file contains the SELinux security data structures for kernel objects.
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*
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* Author(s): Stephen Smalley, <sds@epoch.ncsc.mil>
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* Chris Vance, <cvance@nai.com>
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* Wayne Salamon, <wsalamon@nai.com>
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* James Morris <jmorris@redhat.com>
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*
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* Copyright (C) 2001,2002 Networks Associates Technology, Inc.
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* Copyright (C) 2003 Red Hat, Inc., James Morris <jmorris@redhat.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2,
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* as published by the Free Software Foundation.
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*/
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#ifndef _SELINUX_OBJSEC_H_
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#define _SELINUX_OBJSEC_H_
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#include <linux/list.h>
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#include <linux/sched.h>
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#include <linux/fs.h>
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#include <linux/binfmts.h>
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#include <linux/in.h>
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#include <linux/spinlock.h>
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#include "flask.h"
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#include "avc.h"
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struct task_security_struct {
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u32 osid; /* SID prior to last execve */
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u32 sid; /* current SID */
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u32 exec_sid; /* exec SID */
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u32 create_sid; /* fscreate SID */
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u32 keycreate_sid; /* keycreate SID */
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u32 sockcreate_sid; /* fscreate SID */
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};
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struct inode_security_struct {
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struct inode *inode; /* back pointer to inode object */
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struct list_head list; /* list of inode_security_struct */
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u32 task_sid; /* SID of creating task */
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u32 sid; /* SID of this object */
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u16 sclass; /* security class of this object */
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unsigned char initialized; /* initialization flag */
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struct mutex lock;
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};
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struct file_security_struct {
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u32 sid; /* SID of open file description */
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u32 fown_sid; /* SID of file owner (for SIGIO) */
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u32 isid; /* SID of inode at the time of file open */
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u32 pseqno; /* Policy seqno at the time of file open */
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};
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struct superblock_security_struct {
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struct super_block *sb; /* back pointer to sb object */
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struct list_head list; /* list of superblock_security_struct */
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u32 sid; /* SID of file system superblock */
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u32 def_sid; /* default SID for labeling */
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u32 mntpoint_sid; /* SECURITY_FS_USE_MNTPOINT context for files */
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unsigned int behavior; /* labeling behavior */
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unsigned char initialized; /* initialization flag */
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unsigned char flags; /* which mount options were specified */
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unsigned char proc; /* proc fs */
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struct mutex lock;
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struct list_head isec_head;
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spinlock_t isec_lock;
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};
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struct msg_security_struct {
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u32 sid; /* SID of message */
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};
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struct ipc_security_struct {
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u16 sclass; /* security class of this object */
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u32 sid; /* SID of IPC resource */
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};
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struct netif_security_struct {
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int ifindex; /* device index */
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u32 sid; /* SID for this interface */
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};
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struct netnode_security_struct {
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union {
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__be32 ipv4; /* IPv4 node address */
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struct in6_addr ipv6; /* IPv6 node address */
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} addr;
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u32 sid; /* SID for this node */
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u16 family; /* address family */
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};
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struct netport_security_struct {
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u32 sid; /* SID for this node */
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u16 port; /* port number */
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u8 protocol; /* transport protocol */
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};
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struct sk_security_struct {
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#ifdef CONFIG_NETLABEL
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enum { /* NetLabel state */
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NLBL_UNSET = 0,
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NLBL_REQUIRE,
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NLBL_LABELED,
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NLBL_REQSKB,
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NLBL_CONNLABELED,
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} nlbl_state;
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struct netlbl_lsm_secattr *nlbl_secattr; /* NetLabel sec attributes */
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#endif
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u32 sid; /* SID of this object */
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u32 peer_sid; /* SID of peer */
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u16 sclass; /* sock security class */
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};
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struct key_security_struct {
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u32 sid; /* SID of key */
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};
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extern unsigned int selinux_checkreqprot;
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#endif /* _SELINUX_OBJSEC_H_ */
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