1 files changed, 39 insertions, 21 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index e9afe63da24b..8e95855ff3cf 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -179,6 +179,11 @@ int next_signal(struct sigpending *pending, sigset_t *mask)
         return sig;
 }
 
+/*
+ * allocate a new signal queue record
+ * - this may be called without locks if and only if t == current, otherwise an
+ *   appopriate lock must be held to stop the target task from exiting
+ */
 static struct sigqueue *__sigqueue_alloc(struct task_struct *t, gfp_t flags,
                                          int override_rlimit)
 {
@@ -186,11 +191,12 @@ static struct sigqueue *__sigqueue_alloc(struct task_struct *t, gfp_t flags,
         struct user_struct *user;
 
         /*
-         * In order to avoid problems with "switch_user()", we want to make
-         * sure that the compiler doesn't re-load "t->user"
+         * We won't get problems with the target's UID changing under us
+         * because changing it requires RCU be used, and if t != current, the
+         * caller must be holding the RCU readlock (by way of a spinlock) and
+         * we use RCU protection here
          */
-        user = t->user;
-        barrier();
+        user = get_uid(__task_cred(t)->user);
         atomic_inc(&user->sigpending);
         if (override_rlimit ||
             atomic_read(&user->sigpending) <=
@@ -198,12 +204,14 @@ static struct sigqueue *__sigqueue_alloc(struct task_struct *t, gfp_t flags,
                 q = kmem_cache_alloc(sigqueue_cachep, flags);
         if (unlikely(q == NULL)) {
                 atomic_dec(&user->sigpending);
+                free_uid(user);
         } else {
                 INIT_LIST_HEAD(&q->list);
                 q->flags = 0;
-                q->user = get_uid(user);
+                q->user = user;
         }
-        return(q);
+
+        return q;
 }
 
 static void __sigqueue_free(struct sigqueue *q)
@@ -564,10 +572,12 @@ static int rm_from_queue(unsigned long mask, struct sigpending *s)
 
 /*
  * Bad permissions for sending the signal
+ * - the caller must hold at least the RCU read lock
  */
 static int check_kill_permission(int sig, struct siginfo *info,
                                  struct task_struct *t)
 {
+        const struct cred *cred = current_cred(), *tcred;
         struct pid *sid;
         int error;
 
@@ -581,8 +591,11 @@ static int check_kill_permission(int sig, struct siginfo *info,
         if (error)
                 return error;
 
-        if ((current->euid ^ t->suid) && (current->euid ^ t->uid) &&
-            (current->uid  ^ t->suid) && (current->uid  ^ t->uid) &&
+        tcred = __task_cred(t);
+        if ((cred->euid ^ tcred->suid) &&
+            (cred->euid ^ tcred->uid) &&
+            (cred->uid  ^ tcred->suid) &&
+            (cred->uid  ^ tcred->uid) &&
             !capable(CAP_KILL)) {
                 switch (sig) {
                 case SIGCONT:
@@ -846,7 +859,7 @@ static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
                         q->info.si_errno = 0;
                         q->info.si_code = SI_USER;
                         q->info.si_pid = task_pid_vnr(current);
-                        q->info.si_uid = current->uid;
+                        q->info.si_uid = current_uid();
                         break;
                 case (unsigned long) SEND_SIG_PRIV:
                         q->info.si_signo = sig;
@@ -1010,6 +1023,10 @@ struct sighand_struct *lock_task_sighand(struct task_struct *tsk, unsigned long
         return sighand;
 }
 
+/*
+ * send signal info to all the members of a group
+ * - the caller must hold the RCU read lock at least
+ */
 int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
 {
         unsigned long flags;
@@ -1031,8 +1048,8 @@ int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
 /*
  * __kill_pgrp_info() sends a signal to a process group: this is what the tty
  * control characters do (^C, ^Z etc)
+ * - the caller must hold at least a readlock on tasklist_lock
  */
-
 int __kill_pgrp_info(int sig, struct siginfo *info, struct pid *pgrp)
 {
         struct task_struct *p = NULL;
@@ -1088,6 +1105,7 @@ int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
 {
         int ret = -EINVAL;
         struct task_struct *p;
+        const struct cred *pcred;
 
         if (!valid_signal(sig))
                 return ret;
@@ -1098,9 +1116,11 @@ int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
                 ret = -ESRCH;
                 goto out_unlock;
         }
-        if ((info == SEND_SIG_NOINFO || (!is_si_special(info) && SI_FROMUSER(info)))
-            && (euid != p->suid) && (euid != p->uid)
-            && (uid != p->suid) && (uid != p->uid)) {
+        pcred = __task_cred(p);
+        if ((info == SEND_SIG_NOINFO ||
+             (!is_si_special(info) && SI_FROMUSER(info))) &&
+            euid != pcred->suid && euid != pcred->uid &&
+            uid  != pcred->suid && uid  != pcred->uid) {
                 ret = -EPERM;
                 goto out_unlock;
         }
@@ -1371,10 +1391,9 @@ int do_notify_parent(struct task_struct *tsk, int sig)
          */
         rcu_read_lock();
         info.si_pid = task_pid_nr_ns(tsk, tsk->parent->nsproxy->pid_ns);
+        info.si_uid = __task_cred(tsk)->uid;
         rcu_read_unlock();
 
-        info.si_uid = tsk->uid;
-
         thread_group_cputime(tsk, &cputime);
         info.si_utime = cputime_to_jiffies(cputime.utime);
         info.si_stime = cputime_to_jiffies(cputime.stime);
@@ -1442,10 +1461,9 @@ static void do_notify_parent_cldstop(struct task_struct *tsk, int why)
          */
         rcu_read_lock();
         info.si_pid = task_pid_nr_ns(tsk, tsk->parent->nsproxy->pid_ns);
+        info.si_uid = __task_cred(tsk)->uid;
         rcu_read_unlock();
 
-        info.si_uid = tsk->uid;
-
         info.si_utime = cputime_to_clock_t(tsk->utime);
         info.si_stime = cputime_to_clock_t(tsk->stime);
 
@@ -1600,7 +1618,7 @@ void ptrace_notify(int exit_code)
         info.si_signo = SIGTRAP;
         info.si_code = exit_code;
         info.si_pid = task_pid_vnr(current);
-        info.si_uid = current->uid;
+        info.si_uid = current_uid();
 
         /* Let the debugger run.  */
         spin_lock_irq(&current->sighand->siglock);
@@ -1712,7 +1730,7 @@ static int ptrace_signal(int signr, siginfo_t *info,
                 info->si_errno = 0;
                 info->si_code = SI_USER;
                 info->si_pid = task_pid_vnr(current->parent);
-                info->si_uid = current->parent->uid;
+                info->si_uid = task_uid(current->parent);
         }
 
         /* If the (new) signal is now blocked, requeue it.  */
@@ -2213,7 +2231,7 @@ sys_kill(pid_t pid, int sig)
         info.si_errno = 0;
         info.si_code = SI_USER;
         info.si_pid = task_tgid_vnr(current);
-        info.si_uid = current->uid;
+        info.si_uid = current_uid();
 
         return kill_something_info(sig, &info, pid);
 }
@@ -2230,7 +2248,7 @@ static int do_tkill(pid_t tgid, pid_t pid, int sig)
         info.si_errno = 0;
         info.si_code = SI_TKILL;
         info.si_pid = task_tgid_vnr(current);
-        info.si_uid = current->uid;
+        info.si_uid = current_uid();
 
         rcu_read_lock();
         p = find_task_by_vpid(pid);