CRED: Use RCU to access another task's creds and to release a task's own creds

Use RCU to access another task's creds and to release a task's own creds.
This means that it will be possible for the credentials of a task to be
replaced without another task (a) requiring a full lock to read them, and (b)
seeing deallocated memory.

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>

5 files changed, 86 insertions, 57 deletions

diff --git a/security/commoncap.c b/security/commoncap.c
index 61307f590003..0384bf95db68 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -51,10 +51,13 @@ EXPORT_SYMBOL(cap_netlink_recv);
  */
 int cap_capable(struct task_struct *tsk, int cap, int audit)
 {
+        __u32 cap_raised;
+
         /* Derived from include/linux/sched.h:capable. */
-        if (cap_raised(tsk->cred->cap_effective, cap))
-                return 0;
-        return -EPERM;
+        rcu_read_lock();
+        cap_raised = cap_raised(__task_cred(tsk)->cap_effective, cap);
+        rcu_read_unlock();
+        return cap_raised ? 0 : -EPERM;
 }
 
 int cap_settime(struct timespec *ts, struct timezone *tz)
@@ -66,34 +69,42 @@ int cap_settime(struct timespec *ts, struct timezone *tz)
 
 int cap_ptrace_may_access(struct task_struct *child, unsigned int mode)
 {
-        /* Derived from arch/i386/kernel/ptrace.c:sys_ptrace. */
-        if (cap_issubset(child->cred->cap_permitted,
-                         current->cred->cap_permitted))
-                return 0;
-        if (capable(CAP_SYS_PTRACE))
-                return 0;
-        return -EPERM;
+        int ret = 0;
+
+        rcu_read_lock();
+        if (!cap_issubset(child->cred->cap_permitted,
+                          current->cred->cap_permitted) &&
+            !capable(CAP_SYS_PTRACE))
+                ret = -EPERM;
+        rcu_read_unlock();
+        return ret;
 }
 
 int cap_ptrace_traceme(struct task_struct *parent)
 {
-        if (cap_issubset(current->cred->cap_permitted,
-                         parent->cred->cap_permitted))
-                return 0;
-        if (has_capability(parent, CAP_SYS_PTRACE))
-                return 0;
-        return -EPERM;
+        int ret = 0;
+
+        rcu_read_lock();
+        if (!cap_issubset(current->cred->cap_permitted,
+                         parent->cred->cap_permitted) &&
+            !has_capability(parent, CAP_SYS_PTRACE))
+                ret = -EPERM;
+        rcu_read_unlock();
+        return ret;
 }
 
 int cap_capget (struct task_struct *target, kernel_cap_t *effective,
                 kernel_cap_t *inheritable, kernel_cap_t *permitted)
 {
-        struct cred *cred = target->cred;
+        const struct cred *cred;
 
         /* Derived from kernel/capability.c:sys_capget. */
+        rcu_read_lock();
+        cred = __task_cred(target);
         *effective   = cred->cap_effective;
         *inheritable = cred->cap_inheritable;
         *permitted   = cred->cap_permitted;
+        rcu_read_unlock();
         return 0;
 }
 
@@ -433,7 +444,7 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
 
 int cap_bprm_secureexec (struct linux_binprm *bprm)
 {
-        const struct cred *cred = current->cred;
+        const struct cred *cred = current_cred();
 
         if (cred->uid != 0) {
                 if (bprm->cap_effective)
@@ -511,11 +522,11 @@ static inline void cap_emulate_setxuid (int old_ruid, int old_euid,
         if ((old_ruid == 0 || old_euid == 0 || old_suid == 0) &&
             (cred->uid != 0 && cred->euid != 0 && cred->suid != 0) &&
             !issecure(SECURE_KEEP_CAPS)) {
-                cap_clear (cred->cap_permitted);
-                cap_clear (cred->cap_effective);
+                cap_clear(cred->cap_permitted);
+                cap_clear(cred->cap_effective);
         }
         if (old_euid == 0 && cred->euid != 0) {
-                cap_clear (cred->cap_effective);
+                cap_clear(cred->cap_effective);
         }
         if (old_euid != 0 && cred->euid == 0) {
                 cred->cap_effective = cred->cap_permitted;
@@ -582,9 +593,14 @@ int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t old_suid,
  */
 static int cap_safe_nice(struct task_struct *p)
 {
-        if (!cap_issubset(p->cred->cap_permitted,
-                          current->cred->cap_permitted) &&
-            !capable(CAP_SYS_NICE))
+        int is_subset;
+
+        rcu_read_lock();
+        is_subset = cap_issubset(__task_cred(p)->cap_permitted,
+                                 current_cred()->cap_permitted);
+        rcu_read_unlock();
+
+        if (!is_subset && !capable(CAP_SYS_NICE))
                 return -EPERM;
         return 0;
 }
diff --git a/security/keys/permission.c b/security/keys/permission.c
index baf3d5f31e71..13c36164f284 100644
--- a/security/keys/permission.c
+++ b/security/keys/permission.c
@@ -22,13 +22,16 @@ int key_task_permission(const key_ref_t key_ref,
                         struct task_struct *context,
                         key_perm_t perm)
 {
-        struct cred *cred = context->cred;
+        const struct cred *cred;
         struct key *key;
         key_perm_t kperm;
         int ret;
 
         key = key_ref_to_ptr(key_ref);
 
+        rcu_read_lock();
+        cred = __task_cred(context);
+
         /* use the second 8-bits of permissions for keys the caller owns */
         if (key->uid == cred->fsuid) {
                 kperm = key->perm >> 16;
@@ -43,10 +46,7 @@ int key_task_permission(const key_ref_t key_ref,
                         goto use_these_perms;
                 }
 
-                spin_lock(&cred->lock);
                 ret = groups_search(cred->group_info, key->gid);
-                spin_unlock(&cred->lock);
-
                 if (ret) {
                         kperm = key->perm >> 8;
                         goto use_these_perms;
@@ -57,6 +57,8 @@ int key_task_permission(const key_ref_t key_ref,
         kperm = key->perm;
 
 use_these_perms:
+        rcu_read_lock();
+
         /* use the top 8-bits of permissions for keys the caller possesses
          * - possessor permissions are additive with other permissions
          */
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index ce8ac6073d57..212601ebaa46 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -412,10 +412,13 @@ key_ref_t search_process_keyrings(struct key_type *type,
                                   struct task_struct *context)
 {
         struct request_key_auth *rka;
+        struct cred *cred;
         key_ref_t key_ref, ret, err;
 
         might_sleep();
 
+        cred = get_task_cred(context);
+
         /* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
          * searchable, but we failed to find a key or we found a negative key;
          * otherwise we want to return a sample error (probably -EACCES) if
@@ -428,9 +431,9 @@ key_ref_t search_process_keyrings(struct key_type *type,
         err = ERR_PTR(-EAGAIN);
 
         /* search the thread keyring first */
-        if (context->cred->thread_keyring) {
+        if (cred->thread_keyring) {
                 key_ref = keyring_search_aux(
-                        make_key_ref(context->cred->thread_keyring, 1),
+                        make_key_ref(cred->thread_keyring, 1),
                         context, type, description, match);
                 if (!IS_ERR(key_ref))
                         goto found;
@@ -495,9 +498,9 @@ key_ref_t search_process_keyrings(struct key_type *type,
                 }
         }
         /* or search the user-session keyring */
-        else if (context->cred->user->session_keyring) {
+        else if (cred->user->session_keyring) {
                 key_ref = keyring_search_aux(
-                        make_key_ref(context->cred->user->session_keyring, 1),
+                        make_key_ref(cred->user->session_keyring, 1),
                         context, type, description, match);
                 if (!IS_ERR(key_ref))
                         goto found;
@@ -519,20 +522,20 @@ key_ref_t search_process_keyrings(struct key_type *type,
          * search the keyrings of the process mentioned there
          * - we don't permit access to request_key auth keys via this method
          */
-        if (context->cred->request_key_auth &&
+        if (cred->request_key_auth &&
             context == current &&
             type != &key_type_request_key_auth
             ) {
                 /* defend against the auth key being revoked */
-                down_read(&context->cred->request_key_auth->sem);
+                down_read(&cred->request_key_auth->sem);
 
-                if (key_validate(context->cred->request_key_auth) == 0) {
-                        rka = context->cred->request_key_auth->payload.data;
+                if (key_validate(cred->request_key_auth) == 0) {
+                        rka = cred->request_key_auth->payload.data;
 
                         key_ref = search_process_keyrings(type, description,
                                                           match, rka->context);
 
-                        up_read(&context->cred->request_key_auth->sem);
+                        up_read(&cred->request_key_auth->sem);
 
                         if (!IS_ERR(key_ref))
                                 goto found;
@@ -549,7 +552,7 @@ key_ref_t search_process_keyrings(struct key_type *type,
                                 break;
                         }
                 } else {
-                        up_read(&context->cred->request_key_auth->sem);
+                        up_read(&cred->request_key_auth->sem);
                 }
         }
 
@@ -557,6 +560,7 @@ key_ref_t search_process_keyrings(struct key_type *type,
         key_ref = ret ? ret : err;
 
 found:
+        put_cred(cred);
         return key_ref;
 
 } /* end search_process_keyrings() */
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 10715d1330b9..c86303638235 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -95,13 +95,18 @@ extern void selnl_notify_setenforce(int val);
 static int task_has_security(struct task_struct *tsk,
                              u32 perms)
 {
-        struct task_security_struct *tsec;
-
-        tsec = tsk->cred->security;
+        const struct task_security_struct *tsec;
+        u32 sid = 0;
+
+        rcu_read_lock();
+        tsec = __task_cred(tsk)->security;
+        if (tsec)
+                sid = tsec->sid;
+        rcu_read_unlock();
         if (!tsec)
                 return -EACCES;
 
-        return avc_has_perm(tsec->sid, SECINITSID_SECURITY,
+        return avc_has_perm(sid, SECINITSID_SECURITY,
                             SECCLASS_SECURITY, perms, NULL);
 }
 
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index e8a4fcb1ad04..11167fd567b9 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -30,6 +30,8 @@
 
 #include "smack.h"
 
+#define task_security(task)     (task_cred_xxx((task), security))
+
 /*
  * I hope these are the hokeyist lines of code in the module. Casey.
  */
@@ -1012,7 +1014,7 @@ static void smack_cred_free(struct cred *cred)
  */
 static int smack_task_setpgid(struct task_struct *p, pid_t pgid)
 {
-        return smk_curacc(p->cred->security, MAY_WRITE);
+        return smk_curacc(task_security(p), MAY_WRITE);
 }
 
 /**
@@ -1023,7 +1025,7 @@ static int smack_task_setpgid(struct task_struct *p, pid_t pgid)
  */
 static int smack_task_getpgid(struct task_struct *p)
 {
-        return smk_curacc(p->cred->security, MAY_READ);
+        return smk_curacc(task_security(p), MAY_READ);
 }
 
 /**
@@ -1034,7 +1036,7 @@ static int smack_task_getpgid(struct task_struct *p)
  */
 static int smack_task_getsid(struct task_struct *p)
 {
-        return smk_curacc(p->cred->security, MAY_READ);
+        return smk_curacc(task_security(p), MAY_READ);
 }
 
 /**
@@ -1046,7 +1048,7 @@ static int smack_task_getsid(struct task_struct *p)
  */
 static void smack_task_getsecid(struct task_struct *p, u32 *secid)
 {
-        *secid = smack_to_secid(p->cred->security);
+        *secid = smack_to_secid(task_security(p));
 }
 
 /**
@@ -1062,7 +1064,7 @@ static int smack_task_setnice(struct task_struct *p, int nice)
 
         rc = cap_task_setnice(p, nice);
         if (rc == 0)
-                rc = smk_curacc(p->cred->security, MAY_WRITE);
+                rc = smk_curacc(task_security(p), MAY_WRITE);
         return rc;
 }
 
@@ -1079,7 +1081,7 @@ static int smack_task_setioprio(struct task_struct *p, int ioprio)
 
         rc = cap_task_setioprio(p, ioprio);
         if (rc == 0)
-                rc = smk_curacc(p->cred->security, MAY_WRITE);
+                rc = smk_curacc(task_security(p), MAY_WRITE);
         return rc;
 }
 
@@ -1091,7 +1093,7 @@ static int smack_task_setioprio(struct task_struct *p, int ioprio)
  */
 static int smack_task_getioprio(struct task_struct *p)
 {
-        return smk_curacc(p->cred->security, MAY_READ);
+        return smk_curacc(task_security(p), MAY_READ);
 }
 
 /**
@@ -1109,7 +1111,7 @@ static int smack_task_setscheduler(struct task_struct *p, int policy,
 
         rc = cap_task_setscheduler(p, policy, lp);
         if (rc == 0)
-                rc = smk_curacc(p->cred->security, MAY_WRITE);
+                rc = smk_curacc(task_security(p), MAY_WRITE);
         return rc;
 }
 
@@ -1121,7 +1123,7 @@ static int smack_task_setscheduler(struct task_struct *p, int policy,
  */
 static int smack_task_getscheduler(struct task_struct *p)
 {
-        return smk_curacc(p->cred->security, MAY_READ);
+        return smk_curacc(task_security(p), MAY_READ);
 }
 
 /**
@@ -1132,7 +1134,7 @@ static int smack_task_getscheduler(struct task_struct *p)
  */
 static int smack_task_movememory(struct task_struct *p)
 {
-        return smk_curacc(p->cred->security, MAY_WRITE);
+        return smk_curacc(task_security(p), MAY_WRITE);
 }
 
 /**
@@ -1155,13 +1157,13 @@ static int smack_task_kill(struct task_struct *p, struct siginfo *info,
          * can write the receiver.
          */
         if (secid == 0)
-                return smk_curacc(p->cred->security, MAY_WRITE);
+                return smk_curacc(task_security(p), MAY_WRITE);
         /*
          * If the secid isn't 0 we're dealing with some USB IO
          * specific behavior. This is not clean. For one thing
          * we can't take privilege into account.
          */
-        return smk_access(smack_from_secid(secid), p->cred->security, MAY_WRITE);
+        return smk_access(smack_from_secid(secid), task_security(p), MAY_WRITE);
 }
 
 /**
@@ -1174,7 +1176,7 @@ static int smack_task_wait(struct task_struct *p)
 {
         int rc;
 
-        rc = smk_access(current->cred->security, p->cred->security, MAY_WRITE);
+        rc = smk_access(current_security(), task_security(p), MAY_WRITE);
         if (rc == 0)
                 return 0;
 
@@ -1205,7 +1207,7 @@ static int smack_task_wait(struct task_struct *p)
 static void smack_task_to_inode(struct task_struct *p, struct inode *inode)
 {
         struct inode_smack *isp = inode->i_security;
-        isp->smk_inode = p->cred->security;
+        isp->smk_inode = task_security(p);
 }
 
 /*
@@ -2010,7 +2012,7 @@ static int smack_getprocattr(struct task_struct *p, char *name, char **value)
         if (strcmp(name, "current") != 0)
                 return -EINVAL;
 
-        cp = kstrdup(p->cred->security, GFP_KERNEL);
+        cp = kstrdup(task_security(p), GFP_KERNEL);
         if (cp == NULL)
                 return -ENOMEM;