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authorJann Horn <jannh@google.com>2019-04-10 09:55:19 -0700
committerMicah Morton <mortonm@chromium.org>2019-07-15 08:05:37 -0700
commit7ef6b3062fb9f0b9dbaaec182495189459100807 (patch)
tree9db72d7aa7fb324f41d698951d8f572c4509168d /security
parentc783d525f9e7e1fd6a5dc3379f3c1fb041495b76 (diff)
LSM: SafeSetID: fix check for setresuid(new1, new2, new3)
With the old code, when a process with the (real,effective,saved) UID set (1,1,1) calls setresuid(2,3,4), safesetid_task_fix_setuid() only checks whether the transition 1->2 is permitted; the transitions 1->3 and 1->4 are not checked. Fix this. This is also a good opportunity to refactor safesetid_task_fix_setuid() to be less verbose - having one branch per set*uid() syscall is unnecessary. Note that this slightly changes semantics: The UID transition check for UIDs that were not in the old cred struct is now always performed against the policy of the RUID. I think that's more consistent anyway, since the RUID is also the one that decides whether any policy is enforced at all. Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Micah Morton <mortonm@chromium.org>
Diffstat (limited to 'security')
-rw-r--r--security/safesetid/lsm.c125
1 files changed, 35 insertions, 90 deletions
diff --git a/security/safesetid/lsm.c b/security/safesetid/lsm.c
index ac55bf193213..0770447d51f0 100644
--- a/security/safesetid/lsm.c
+++ b/security/safesetid/lsm.c
@@ -99,20 +99,30 @@ static int safesetid_security_capable(const struct cred *cred,
return 0;
}
-static int check_uid_transition(kuid_t parent, kuid_t child)
+/*
+ * Check whether a caller with old credentials @old is allowed to switch to
+ * credentials that contain @new_uid.
+ */
+static bool uid_permitted_for_cred(const struct cred *old, kuid_t new_uid)
{
- if (check_setuid_policy_hashtable_key_value(parent, child))
- return 0;
- pr_warn("UID transition (%d -> %d) blocked\n",
- __kuid_val(parent),
- __kuid_val(child));
+ bool permitted;
+
+ /* If our old creds already had this UID in it, it's fine. */
+ if (uid_eq(new_uid, old->uid) || uid_eq(new_uid, old->euid) ||
+ uid_eq(new_uid, old->suid))
+ return true;
+
/*
- * Kill this process to avoid potential security vulnerabilities
- * that could arise from a missing whitelist entry preventing a
- * privileged process from dropping to a lesser-privileged one.
+ * Transitions to new UIDs require a check against the policy of the old
+ * RUID.
*/
- force_sig(SIGKILL);
- return -EACCES;
+ permitted = check_setuid_policy_hashtable_key_value(old->uid, new_uid);
+ if (!permitted) {
+ pr_warn("UID transition ((%d,%d,%d) -> %d) blocked\n",
+ __kuid_val(old->uid), __kuid_val(old->euid),
+ __kuid_val(old->suid), __kuid_val(new_uid));
+ }
+ return permitted;
}
/*
@@ -125,88 +135,23 @@ static int safesetid_task_fix_setuid(struct cred *new,
int flags)
{
- /* Do nothing if there are no setuid restrictions for this UID. */
+ /* Do nothing if there are no setuid restrictions for our old RUID. */
if (!check_setuid_policy_hashtable_key(old->uid))
return 0;
- switch (flags) {
- case LSM_SETID_RE:
- /*
- * Users for which setuid restrictions exist can only set the
- * real UID to the real UID or the effective UID, unless an
- * explicit whitelist policy allows the transition.
- */
- if (!uid_eq(old->uid, new->uid) &&
- !uid_eq(old->euid, new->uid)) {
- return check_uid_transition(old->uid, new->uid);
- }
- /*
- * Users for which setuid restrictions exist can only set the
- * effective UID to the real UID, the effective UID, or the
- * saved set-UID, unless an explicit whitelist policy allows
- * the transition.
- */
- if (!uid_eq(old->uid, new->euid) &&
- !uid_eq(old->euid, new->euid) &&
- !uid_eq(old->suid, new->euid)) {
- return check_uid_transition(old->euid, new->euid);
- }
- break;
- case LSM_SETID_ID:
- /*
- * Users for which setuid restrictions exist cannot change the
- * real UID or saved set-UID unless an explicit whitelist
- * policy allows the transition.
- */
- if (!uid_eq(old->uid, new->uid))
- return check_uid_transition(old->uid, new->uid);
- if (!uid_eq(old->suid, new->suid))
- return check_uid_transition(old->suid, new->suid);
- break;
- case LSM_SETID_RES:
- /*
- * Users for which setuid restrictions exist cannot change the
- * real UID, effective UID, or saved set-UID to anything but
- * one of: the current real UID, the current effective UID or
- * the current saved set-user-ID unless an explicit whitelist
- * policy allows the transition.
- */
- if (!uid_eq(new->uid, old->uid) &&
- !uid_eq(new->uid, old->euid) &&
- !uid_eq(new->uid, old->suid)) {
- return check_uid_transition(old->uid, new->uid);
- }
- if (!uid_eq(new->euid, old->uid) &&
- !uid_eq(new->euid, old->euid) &&
- !uid_eq(new->euid, old->suid)) {
- return check_uid_transition(old->euid, new->euid);
- }
- if (!uid_eq(new->suid, old->uid) &&
- !uid_eq(new->suid, old->euid) &&
- !uid_eq(new->suid, old->suid)) {
- return check_uid_transition(old->suid, new->suid);
- }
- break;
- case LSM_SETID_FS:
- /*
- * Users for which setuid restrictions exist cannot change the
- * filesystem UID to anything but one of: the current real UID,
- * the current effective UID or the current saved set-UID
- * unless an explicit whitelist policy allows the transition.
- */
- if (!uid_eq(new->fsuid, old->uid) &&
- !uid_eq(new->fsuid, old->euid) &&
- !uid_eq(new->fsuid, old->suid) &&
- !uid_eq(new->fsuid, old->fsuid)) {
- return check_uid_transition(old->fsuid, new->fsuid);
- }
- break;
- default:
- pr_warn("Unknown setid state %d\n", flags);
- force_sig(SIGKILL);
- return -EINVAL;
- }
- return 0;
+ if (uid_permitted_for_cred(old, new->uid) &&
+ uid_permitted_for_cred(old, new->euid) &&
+ uid_permitted_for_cred(old, new->suid) &&
+ uid_permitted_for_cred(old, new->fsuid))
+ return 0;
+
+ /*
+ * Kill this process to avoid potential security vulnerabilities
+ * that could arise from a missing whitelist entry preventing a
+ * privileged process from dropping to a lesser-privileged one.
+ */
+ force_sig(SIGKILL);
+ return -EACCES;
}
int add_safesetid_whitelist_entry(kuid_t parent, kuid_t child)