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2008-10-11Merge branch 'master' of ↵James Morris
git://git.infradead.org/users/pcmoore/lblnet-2.6_next into next
2008-10-10netlabel: Replace protocol/NetLabel linking with refrerence countsPaul Moore
NetLabel has always had a list of backpointers in the CIPSO DOI definition structure which pointed to the NetLabel LSM domain mapping structures which referenced the CIPSO DOI struct. The rationale for this was that when an administrator removed a CIPSO DOI from the system all of the associated NetLabel LSM domain mappings should be removed as well; a list of backpointers made this a simple operation. Unfortunately, while the backpointers did make the removal easier they were a bit of a mess from an implementation point of view which was making further development difficult. Since the removal of a CIPSO DOI is a realtively rare event it seems to make sense to remove this backpointer list as the optimization was hurting us more then it was helping. However, we still need to be able to track when a CIPSO DOI definition is being used so replace the backpointer list with a reference count. In order to preserve the current functionality of removing the associated LSM domain mappings when a CIPSO DOI is removed we walk the LSM domain mapping table, removing the relevant entries. Signed-off-by: Paul Moore <paul.moore@hp.com> Reviewed-by: James Morris <jmorris@namei.org>
2008-10-10smack: Fix missing calls to netlbl_skbuff_err()Paul Moore
Smack needs to call netlbl_skbuff_err() to let NetLabel do the necessary protocol specific error handling. Signed-off-by: Paul Moore <paul.moore@hp.com> Acked-by: Casey Schaufler <casey@schaufler-ca.com>
2008-08-28Merge branch 'master' into nextJames Morris
2008-08-14security: Fix setting of PF_SUPERPRIV by __capable()David Howells
Fix the setting of PF_SUPERPRIV by __capable() as it could corrupt the flags the target process if that is not the current process and it is trying to change its own flags in a different way at the same time. __capable() is using neither atomic ops nor locking to protect t->flags. This patch removes __capable() and introduces has_capability() that doesn't set PF_SUPERPRIV on the process being queried. This patch further splits security_ptrace() in two: (1) security_ptrace_may_access(). This passes judgement on whether one process may access another only (PTRACE_MODE_ATTACH for ptrace() and PTRACE_MODE_READ for /proc), and takes a pointer to the child process. current is the parent. (2) security_ptrace_traceme(). This passes judgement on PTRACE_TRACEME only, and takes only a pointer to the parent process. current is the child. In Smack and commoncap, this uses has_capability() to determine whether the parent will be permitted to use PTRACE_ATTACH if normal checks fail. This does not set PF_SUPERPRIV. Two of the instances of __capable() actually only act on current, and so have been changed to calls to capable(). Of the places that were using __capable(): (1) The OOM killer calls __capable() thrice when weighing the killability of a process. All of these now use has_capability(). (2) cap_ptrace() and smack_ptrace() were using __capable() to check to see whether the parent was allowed to trace any process. As mentioned above, these have been split. For PTRACE_ATTACH and /proc, capable() is now used, and for PTRACE_TRACEME, has_capability() is used. (3) cap_safe_nice() only ever saw current, so now uses capable(). (4) smack_setprocattr() rejected accesses to tasks other than current just after calling __capable(), so the order of these two tests have been switched and capable() is used instead. (5) In smack_file_send_sigiotask(), we need to allow privileged processes to receive SIGIO on files they're manipulating. (6) In smack_task_wait(), we let a process wait for a privileged process, whether or not the process doing the waiting is privileged. I've tested this with the LTP SELinux and syscalls testscripts. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Serge Hallyn <serue@us.ibm.com> Acked-by: Casey Schaufler <casey@schaufler-ca.com> Acked-by: Andrew G. Morgan <morgan@kernel.org> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: James Morris <jmorris@namei.org>
2008-08-05smack: limit privilege by labelCasey Schaufler
There have been a number of requests to make the Smack LSM enforce MAC even in the face of privilege, either capability based or superuser based. This is not universally desired, however, so it seems desirable to make it optional. Further, at least one legacy OS implemented a scheme whereby only processes running with one particular label could be exempt from MAC. This patch supports these three cases. If /smack/onlycap is empty (unset or null-string) privilege is enforced in the normal way. If /smack/onlycap contains a label only processes running with that label may be MAC exempt. If the label in /smack/onlycap is the star label ("*") the semantics of the star label combine with the privilege restrictions to prevent any violations of MAC, even in the presence of privilege. Again, this will be independent of the privilege scheme. Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> Reviewed-by: James Morris <jmorris@namei.org>
2008-07-26[PATCH] pass MAY_OPEN to vfs_permission() explicitlyAl Viro
... and get rid of the last "let's deduce mask from nameidata->flags" bit. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2008-07-14security: remove register_security hookJames Morris
The register security hook is no longer required, as the capability module is always registered. LSMs wishing to stack capability as a secondary module should do so explicitly. Signed-off-by: James Morris <jmorris@namei.org> Acked-by: Stephen Smalley <sds@tycho.nsa.gov> Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
2008-07-14Security: split proc ptrace checking into read vs. attachStephen Smalley
Enable security modules to distinguish reading of process state via proc from full ptrace access by renaming ptrace_may_attach to ptrace_may_access and adding a mode argument indicating whether only read access or full attach access is requested. This allows security modules to permit access to reading process state without granting full ptrace access. The base DAC/capability checking remains unchanged. Read access to /proc/pid/mem continues to apply a full ptrace attach check since check_mem_permission() already requires the current task to already be ptracing the target. The other ptrace checks within proc for elements like environ, maps, and fds are changed to pass the read mode instead of attach. In the SELinux case, we model such reading of process state as a reading of a proc file labeled with the target process' label. This enables SELinux policy to permit such reading of process state without permitting control or manipulation of the target process, as there are a number of cases where programs probe for such information via proc but do not need to be able to control the target (e.g. procps, lsof, PolicyKit, ConsoleKit). At present we have to choose between allowing full ptrace in policy (more permissive than required/desired) or breaking functionality (or in some cases just silencing the denials via dontaudit rules but this can hide genuine attacks). This version of the patch incorporates comments from Casey Schaufler (change/replace existing ptrace_may_attach interface, pass access mode), and Chris Wright (provide greater consistency in the checking). Note that like their predecessors __ptrace_may_attach and ptrace_may_attach, the __ptrace_may_access and ptrace_may_access interfaces use different return value conventions from each other (0 or -errno vs. 1 or 0). I retained this difference to avoid any changes to the caller logic but made the difference clearer by changing the latter interface to return a bool rather than an int and by adding a comment about it to ptrace.h for any future callers. Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov> Acked-by: Chris Wright <chrisw@sous-sol.org> Signed-off-by: James Morris <jmorris@namei.org>
2008-06-04Smack: fuse mount hang fixCasey Schaufler
The d_instantiate hook for Smack can hang on the root inode of a filesystem if the file system code has not really done all the set-up. Fuse is known to encounter this problem. This change detects an attempt to instantiate a root inode and addresses it early in the processing, before any attempt is made to do something that might hang. Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> Tested-by: Luiz Fernando N. Capitulino <lcapitulino@mandriva.com.br> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-04-30signals: cleanup security_task_kill() usage/implementationOleg Nesterov
Every implementation of ->task_kill() does nothing when the signal comes from the kernel. This is correct, but means that check_kill_permission() should call security_task_kill() only for SI_FROMUSER() case, and we can remove the same check from ->task_kill() implementations. (sadly, check_kill_permission() is the last user of signal->session/__session but we can't s/task_session_nr/task_session/ here). NOTE: Eric W. Biederman pointed out cap_task_kill() should die, and I think he is very right. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Serge Hallyn <serue@us.ibm.com> Cc: Roland McGrath <roland@redhat.com> Cc: Casey Schaufler <casey@schaufler-ca.com> Cc: David Quigley <dpquigl@tycho.nsa.gov> Cc: Eric Paris <eparis@redhat.com> Cc: Harald Welte <laforge@gnumonks.org> Cc: Pavel Emelyanov <xemul@openvz.org> Cc: Stephen Smalley <sds@tycho.nsa.gov> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-04-30Smack: Integrate Smack with AuditAhmed S. Darwish
Setup the new Audit hooks for Smack. SELinux Audit rule fields are recycled to avoid `auditd' userspace modifications. Currently only equality testing is supported on labels acting as a subject (AUDIT_SUBJ_USER) or as an object (AUDIT_OBJ_USER). Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com> Acked-by: Casey Schaufler <casey@schaufler-ca.com>
2008-04-30Security: Make secctx_to_secid() take const secdataDavid Howells
Make secctx_to_secid() take constant secdata. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: James Morris <jmorris@namei.org>
2008-04-29Merge branch 'audit.b50' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/viro/audit-current * 'audit.b50' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/audit-current: [PATCH] new predicate - AUDIT_FILETYPE [patch 2/2] Use find_task_by_vpid in audit code [patch 1/2] audit: let userspace fully control TTY input auditing [PATCH 2/2] audit: fix sparse shadowed variable warnings [PATCH 1/2] audit: move extern declarations to audit.h Audit: MAINTAINERS update Audit: increase the maximum length of the key field Audit: standardize string audit interfaces Audit: stop deadlock from signals under load Audit: save audit_backlog_limit audit messages in case auditd comes back Audit: collect sessionid in netlink messages Audit: end printk with newline
2008-04-29xattr: add missing consts to function argumentsDavid Howells
Add missing consts to xattr function arguments. Signed-off-by: David Howells <dhowells@redhat.com> Cc: Andreas Gruenbacher <agruen@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-04-28smack: use cap_task_prctlSerge E. Hallyn
With the introduction of per-process securebits, the capabilities-related prctl callbacks were moved into cap_task_prctl(). Have smack use cap_task_prctl() so that PR_SET_KEEPCAPS is defined. Signed-off-by: Serge E. Hallyn <serue@us.ibm.com> Acked-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-04-28smack: make smk_cipso_doi() and smk_unlbl_ambient()Casey Schaufler
The functions smk_cipso_doi and smk_unlbl_ambient are not used outside smackfs.c and should hence be static. Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-04-28smack: fix integer as NULL pointer warning in smack_lsm.cHarvey Harrison
security/smack/smack_lsm.c:1257:16: warning: Using plain integer as NULL pointer Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com> Acked-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-04-28Audit: collect sessionid in netlink messagesEric Paris
Previously I added sessionid output to all audit messages where it was available but we still didn't know the sessionid of the sender of netlink messages. This patch adds that information to netlink messages so we can audit who sent netlink messages. Signed-off-by: Eric Paris <eparis@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2008-04-21[PATCH] switch a bunch of LSM hooks from nameidata to pathAl Viro
Namely, ones from namespace.c Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2008-04-18Merge branch 'for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6 * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6: security: fix up documentation for security_module_enable Security: Introduce security= boot parameter Audit: Final renamings and cleanup SELinux: use new audit hooks, remove redundant exports Audit: internally use the new LSM audit hooks LSM/Audit: Introduce generic Audit LSM hooks SELinux: remove redundant exports Netlink: Use generic LSM hook Audit: use new LSM hooks instead of SELinux exports SELinux: setup new inode/ipc getsecid hooks LSM: Introduce inode_getsecid and ipc_getsecid hooks
2008-04-19Security: Introduce security= boot parameterAhmed S. Darwish
Add the security= boot parameter. This is done to avoid LSM registration clashes in case of more than one bult-in module. User can choose a security module to enable at boot. If no security= boot parameter is specified, only the first LSM asking for registration will be loaded. An invalid security module name will be treated as if no module has been chosen. LSM modules must check now if they are allowed to register by calling security_module_enable(ops) first. Modify SELinux and SMACK to do so. Do not let SMACK register smackfs if it was not chosen on boot. Smackfs assumes that smack hooks are registered and the initial task security setup (swapper->security) is done. Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com> Acked-by: James Morris <jmorris@namei.org>
2008-04-12NetLabel: Allow passing the LSM domain as a shared pointerPaul Moore
Smack doesn't have the need to create a private copy of the LSM "domain" when setting NetLabel security attributes like SELinux, however, the current NetLabel code requires a private copy of the LSM "domain". This patches fixes that by letting the LSM determine how it wants to pass the domain value. * NETLBL_SECATTR_DOMAIN_CPY The current behavior, NetLabel assumes that the domain value is a copy and frees it when done * NETLBL_SECATTR_DOMAIN New, Smack-friendly behavior, NetLabel assumes that the domain value is a reference to a string managed by the LSM and does not free it when done Signed-off-by: Paul Moore <paul.moore@hp.com> Acked-by: James Morris <jmorris@namei.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2008-03-24smackfs: remove redundant lock, fix open(,O_RDWR)Ahmed S. Darwish
Older smackfs was parsing MAC rules by characters, thus a need of locking write sessions on open() was needed. This lock is no longer useful now since each rule is handled by a single write() call. This is also a bugfix since seq_open() was not called if an open() O_RDWR flag was given, leading to a seq_read() without an initialized seq_file, thus an Oops. Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com> Reported-by: Jonathan Corbet <corbet@lwn.net> Acked-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-03-20file capabilities: remove cap_task_kill()Serge Hallyn
The original justification for cap_task_kill() was as follows: check_kill_permission() does appropriate uid equivalence checks. However with file capabilities it becomes possible for an unprivileged user to execute a file with file capabilities resulting in a more privileged task with the same uid. However now that cap_task_kill() always returns 0 (permission granted) when p->uid==current->uid, the whole hook is worthless, and only likely to create more subtle problems in the corner cases where it might still be called but return -EPERM. Those cases are basically when uids are different but euid/suid is equivalent as per the check in check_kill_permission(). One example of a still-broken application is 'at' for non-root users. This patch removes cap_task_kill(). Signed-off-by: Serge Hallyn <serge@hallyn.com> Acked-by: Andrew G. Morgan <morgan@kernel.org> Earlier-version-tested-by: Luiz Fernando N. Capitulino <lcapitulino@mandriva.com.br> Acked-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-03-19smack: do not dereference NULL ipc objectAhmed S. Darwish
In the SYSV ipc msgctl(),semctl(),shmctl() family, if the user passed *_INFO as the desired operation, no specific object is meant to be controlled and only system-wide information is returned. This leads to a NULL IPC object in the LSM hooks if the _INFO flag is given. Avoid dereferencing this NULL pointer in Smack ipc *ctl() methods. Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com> Acked-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-03-13smackfs: do not trust `count' in inodes write()sAhmed S. Darwish
Smackfs write() implementation does not put a higher bound on the number of bytes to copy from user-space. This may lead to a DOS attack if a malicious `count' field is given. Assure that given `count' is exactly the length needed for a /smack/load rule. In case of /smack/cipso where the length is relative, assure that `count' does not exceed the size needed for a buffer representing maximum possible number of CIPSO 2.2 categories. Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com> Acked-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-03-06LSM/SELinux: Interfaces to allow FS to control mount optionsEric Paris
Introduce new LSM interfaces to allow an FS to deal with their own mount options. This includes a new string parsing function exported from the LSM that an FS can use to get a security data blob and a new security data blob. This is particularly useful for an FS which uses binary mount data, like NFS, which does not pass strings into the vfs to be handled by the loaded LSM. Also fix a BUG() in both SELinux and SMACK when dealing with binary mount data. If the binary mount data is less than one page the copy_page() in security_sb_copy_data() can cause an illegal page fault and boom. Remove all NFSisms from the SELinux code since they were broken by past NFS changes. Signed-off-by: Eric Paris <eparis@redhat.com> Acked-by: Stephen Smalley <sds@tycho.nsa.gov> Acked-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: James Morris <jmorris@namei.org>
2008-02-23Smack: update for file capabilitiesCasey Schaufler
Update the Smack LSM to allow the registration of the capability "module" as a secondary LSM. Integrate the new hooks required for file based capabilities. Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> Cc: Serge Hallyn <serue@us.ibm.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Paul Moore <paul.moore@hp.com> Cc: James Morris <jmorris@namei.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-02-19Smack: unlabeled outgoing ambient packetsCasey Schaufler
Smack uses CIPSO labeling, but allows for unlabeled packets by specifying an "ambient" label that is applied to incoming unlabeled packets. Because the other end of the connection may dislike IP options, and ssh is one know application that behaves thus, it is prudent to respond in kind. This patch changes the network labeling behavior such that an outgoing packet that would be given a CIPSO label that matches the ambient label is left unlabeled. An "unlbl" domain is added and the netlabel defaulting mechanism invoked rather than assuming that everything is CIPSO. Locking has been added around changes to the ambient label as the mechanisms used to do so are more involved. Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> Acked-by: Paul Moore <paul.moore@hp.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-02-14Embed a struct path into struct nameidata instead of nd->{dentry,mnt}Jan Blunck
This is the central patch of a cleanup series. In most cases there is no good reason why someone would want to use a dentry for itself. This series reflects that fact and embeds a struct path into nameidata. Together with the other patches of this series - it enforced the correct order of getting/releasing the reference count on <dentry,vfsmount> pairs - it prepares the VFS for stacking support since it is essential to have a struct path in every place where the stack can be traversed - it reduces the overall code size: without patch series: text data bss dec hex filename 5321639 858418 715768 6895825 6938d1 vmlinux with patch series: text data bss dec hex filename 5320026 858418 715768 6894212 693284 vmlinux This patch: Switch from nd->{dentry,mnt} to nd->path.{dentry,mnt} everywhere. [akpm@linux-foundation.org: coding-style fixes] [akpm@linux-foundation.org: fix cifs] [akpm@linux-foundation.org: fix smack] Signed-off-by: Jan Blunck <jblunck@suse.de> Signed-off-by: Andreas Gruenbacher <agruen@suse.de> Acked-by: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-02-13Smack: check for 'struct socket' with NULL skAhmed S. Darwish
There's a small problem with smack and NFS. A similar report was also sent here: http://lkml.org/lkml/2007/10/27/85 I've also added similar checks in inode_{get/set}security(). Cheating from SELinux post_create_socket(), it does the same. [akpm@linux-foundation.org: remove uneeded BUG_ON()] Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com> Acked-by: Casey Schaufler <casey@schuafler-ca.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-02-05Smack: Simplified Mandatory Access Control KernelCasey Schaufler
Smack is the Simplified Mandatory Access Control Kernel. Smack implements mandatory access control (MAC) using labels attached to tasks and data containers, including files, SVIPC, and other tasks. Smack is a kernel based scheme that requires an absolute minimum of application support and a very small amount of configuration data. Smack uses extended attributes and provides a set of general mount options, borrowing technics used elsewhere. Smack uses netlabel for CIPSO labeling. Smack provides a pseudo-filesystem smackfs that is used for manipulation of system Smack attributes. The patch, patches for ls and sshd, a README, a startup script, and x86 binaries for ls and sshd are also available on http://www.schaufler-ca.com Development has been done using Fedora Core 7 in a virtual machine environment and on an old Sony laptop. Smack provides mandatory access controls based on the label attached to a task and the label attached to the object it is attempting to access. Smack labels are deliberately short (1-23 characters) text strings. Single character labels using special characters are reserved for system use. The only operation applied to Smack labels is equality comparison. No wildcards or expressions, regular or otherwise, are used. Smack labels are composed of printable characters and may not include "/". A file always gets the Smack label of the task that created it. Smack defines and uses these labels: "*" - pronounced "star" "_" - pronounced "floor" "^" - pronounced "hat" "?" - pronounced "huh" The access rules enforced by Smack are, in order: 1. Any access requested by a task labeled "*" is denied. 2. A read or execute access requested by a task labeled "^" is permitted. 3. A read or execute access requested on an object labeled "_" is permitted. 4. Any access requested on an object labeled "*" is permitted. 5. Any access requested by a task on an object with the same label is permitted. 6. Any access requested that is explicitly defined in the loaded rule set is permitted. 7. Any other access is denied. Rules may be explicitly defined by writing subject,object,access triples to /smack/load. Smack rule sets can be easily defined that describe Bell&LaPadula sensitivity, Biba integrity, and a variety of interesting configurations. Smack rule sets can be modified on the fly to accommodate changes in the operating environment or even the time of day. Some practical use cases: Hierarchical levels. The less common of the two usual uses for MLS systems is to define hierarchical levels, often unclassified, confidential, secret, and so on. To set up smack to support this, these rules could be defined: C Unclass rx S C rx S Unclass rx TS S rx TS C rx TS Unclass rx A TS process can read S, C, and Unclass data, but cannot write it. An S process can read C and Unclass. Note that specifying that TS can read S and S can read C does not imply TS can read C, it has to be explicitly stated. Non-hierarchical categories. This is the more common of the usual uses for an MLS system. Since the default rule is that a subject cannot access an object with a different label no access rules are required to implement compartmentalization. A case that the Bell & LaPadula policy does not allow is demonstrated with this Smack access rule: A case that Bell&LaPadula does not allow that Smack does: ESPN ABC r ABC ESPN r On my portable video device I have two applications, one that shows ABC programming and the other ESPN programming. ESPN wants to show me sport stories that show up as news, and ABC will only provide minimal information about a sports story if ESPN is covering it. Each side can look at the other's info, neither can change the other. Neither can see what FOX is up to, which is just as well all things considered. Another case that I especially like: SatData Guard w Guard Publish w A program running with the Guard label opens a UDP socket and accepts messages sent by a program running with a SatData label. The Guard program inspects the message to ensure it is wholesome and if it is sends it to a program running with the Publish label. This program then puts the information passed in an appropriate place. Note that the Guard program cannot write to a Publish file system object because file system semanitic require read as well as write. The four cases (categories, levels, mutual read, guardbox) here are all quite real, and problems I've been asked to solve over the years. The first two are easy to do with traditonal MLS systems while the last two you can't without invoking privilege, at least for a while. Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> Cc: Joshua Brindle <method@manicmethod.com> Cc: Paul Moore <paul.moore@hp.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Chris Wright <chrisw@sous-sol.org> Cc: James Morris <jmorris@namei.org> Cc: "Ahmed S. Darwish" <darwish.07@gmail.com> Cc: Andrew G. Morgan <morgan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>