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Commit 40852275 authored by Micah Morton's avatar Micah Morton Committed by James Morris
Browse files

LSM: add SafeSetID module that gates setid calls 



This change ensures that the set*uid family of syscalls in kernel/sys.c
(setreuid, setuid, setresuid, setfsuid) all call ns_capable_common with
the CAP_OPT_INSETID flag, so capability checks in the security_capable
hook can know whether they are being called from within a set*uid
syscall. This change is a no-op by itself, but is needed for the
proposed SafeSetID LSM.

Signed-off-by: default avatarMicah Morton <mortonm@chromium.org>
Acked-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarJames Morris <james.morris@microsoft.com>
parent 4b425641

include/linux/capability.h

+5 −0
Original line number Diff line number Diff line
@@ -209,6 +209,7 @@ extern bool has_ns_capability_noaudit(struct task_struct *t, 
extern bool capable(int cap);

extern bool ns_capable(struct user_namespace *ns, int cap);

extern bool ns_capable_noaudit(struct user_namespace *ns, int cap);

extern bool ns_capable_setid(struct user_namespace *ns, int cap);

#else

static inline bool has_capability(struct task_struct *t, int cap)

{
@@ -240,6 +241,10 @@ static inline bool ns_capable_noaudit(struct user_namespace *ns, int cap) 
{

	return true;

}

static inline bool ns_capable_setid(struct user_namespace *ns, int cap)

{

	return true;

}

#endif /* CONFIG_MULTIUSER */

extern bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct inode *inode);

extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);

kernel/capability.c

+19 −0
Original line number Diff line number Diff line
@@ -415,6 +415,25 @@ bool ns_capable_noaudit(struct user_namespace *ns, int cap) 
}

EXPORT_SYMBOL(ns_capable_noaudit);



/**

 * ns_capable_setid - Determine if the current task has a superior capability

 * in effect, while signalling that this check is being done from within a

 * setid syscall.

 * @ns:  The usernamespace we want the capability in

 * @cap: The capability to be tested for

 *

 * Return true if the current task has the given superior capability currently

 * available for use, false if not.

 *

 * This sets PF_SUPERPRIV on the task if the capability is available on the

 * assumption that it's about to be used.

 */

bool ns_capable_setid(struct user_namespace *ns, int cap)

{

	return ns_capable_common(ns, cap, CAP_OPT_INSETID);

}

EXPORT_SYMBOL(ns_capable_setid);



/**

 * capable - Determine if the current task has a superior capability in effect

 * @cap: The capability to be tested for

kernel/sys.c

+5 −5
Original line number Diff line number Diff line
@@ -516,7 +516,7 @@ long __sys_setreuid(uid_t ruid, uid_t euid) 
		new->uid = kruid;

		if (!uid_eq(old->uid, kruid) &&

		    !uid_eq(old->euid, kruid) &&

		    !ns_capable(old->user_ns, CAP_SETUID))

		    !ns_capable_setid(old->user_ns, CAP_SETUID))

			goto error;

	}
@@ -525,7 +525,7 @@ long __sys_setreuid(uid_t ruid, uid_t euid) 
		if (!uid_eq(old->uid, keuid) &&

		    !uid_eq(old->euid, keuid) &&

		    !uid_eq(old->suid, keuid) &&

		    !ns_capable(old->user_ns, CAP_SETUID))

		    !ns_capable_setid(old->user_ns, CAP_SETUID))

			goto error;

	}
@@ -584,7 +584,7 @@ long __sys_setuid(uid_t uid) 
	old = current_cred();



	retval = -EPERM;

	if (ns_capable(old->user_ns, CAP_SETUID)) {

	if (ns_capable_setid(old->user_ns, CAP_SETUID)) {

		new->suid = new->uid = kuid;

		if (!uid_eq(kuid, old->uid)) {

			retval = set_user(new);
@@ -646,7 +646,7 @@ long __sys_setresuid(uid_t ruid, uid_t euid, uid_t suid) 
	old = current_cred();



	retval = -EPERM;

	if (!ns_capable(old->user_ns, CAP_SETUID)) {

	if (!ns_capable_setid(old->user_ns, CAP_SETUID)) {

		if (ruid != (uid_t) -1        && !uid_eq(kruid, old->uid) &&

		    !uid_eq(kruid, old->euid) && !uid_eq(kruid, old->suid))

			goto error;
@@ -814,7 +814,7 @@ long __sys_setfsuid(uid_t uid) 


	if (uid_eq(kuid, old->uid)  || uid_eq(kuid, old->euid)  ||

	    uid_eq(kuid, old->suid) || uid_eq(kuid, old->fsuid) ||

	    ns_capable(old->user_ns, CAP_SETUID)) {

	    ns_capable_setid(old->user_ns, CAP_SETUID)) {

		if (!uid_eq(kuid, old->fsuid)) {

			new->fsuid = kuid;

			if (security_task_fix_setuid(new, old, LSM_SETID_FS) == 0)