CRED: Rename cred_exec_mutex to reflect that it's a guard against ptrace

Rename cred_exec_mutex to reflect that it's a guard against foreign
intervention on a process's credential state, such as is made by ptrace().  The
attachment of a debugger to a process affects execve()'s calculation of the new
credential state - _and_ also setprocattr()'s calculation of that state.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

6 files changed, 20 insertions, 17 deletions

diff --git a/fs/compat.c b/fs/compat.c
index 681ed81e6be0..bb2a9b2e8173 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1488,7 +1488,7 @@ int compat_do_execve(char * filename,
         if (!bprm)
                 goto out_files;
 
-        retval = mutex_lock_interruptible(&current->cred_exec_mutex);
+        retval = mutex_lock_interruptible(&current->cred_guard_mutex);
         if (retval < 0)
                 goto out_free;
         current->in_execve = 1;
@@ -1550,7 +1550,7 @@ int compat_do_execve(char * filename,
         /* execve succeeded */
         current->fs->in_exec = 0;
         current->in_execve = 0;
-        mutex_unlock(&current->cred_exec_mutex);
+        mutex_unlock(&current->cred_guard_mutex);
         acct_update_integrals(current);
         free_bprm(bprm);
         if (displaced)
@@ -1573,7 +1573,7 @@ out_unmark:
 
 out_unlock:
         current->in_execve = 0;
-        mutex_unlock(&current->cred_exec_mutex);
+        mutex_unlock(&current->cred_guard_mutex);
 
 out_free:
         free_bprm(bprm);
diff --git a/fs/exec.c b/fs/exec.c
index 639177b0eeac..998e856c3079 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1045,7 +1045,7 @@ void install_exec_creds(struct linux_binprm *bprm)
         commit_creds(bprm->cred);
         bprm->cred = NULL;
 
-        /* cred_exec_mutex must be held at least to this point to prevent
+        /* cred_guard_mutex must be held at least to this point to prevent
          * ptrace_attach() from altering our determination of the task's
          * credentials; any time after this it may be unlocked */
 
@@ -1055,7 +1055,7 @@ EXPORT_SYMBOL(install_exec_creds);
 
 /*
  * determine how safe it is to execute the proposed program
- * - the caller must hold current->cred_exec_mutex to protect against
+ * - the caller must hold current->cred_guard_mutex to protect against
  *   PTRACE_ATTACH
  */
 int check_unsafe_exec(struct linux_binprm *bprm)
@@ -1297,7 +1297,7 @@ int do_execve(char * filename,
         if (!bprm)
                 goto out_files;
 
-        retval = mutex_lock_interruptible(&current->cred_exec_mutex);
+        retval = mutex_lock_interruptible(&current->cred_guard_mutex);
         if (retval < 0)
                 goto out_free;
         current->in_execve = 1;
@@ -1360,7 +1360,7 @@ int do_execve(char * filename,
         /* execve succeeded */
         current->fs->in_exec = 0;
         current->in_execve = 0;
-        mutex_unlock(&current->cred_exec_mutex);
+        mutex_unlock(&current->cred_guard_mutex);
         acct_update_integrals(current);
         free_bprm(bprm);
         if (displaced)
@@ -1383,7 +1383,7 @@ out_unmark:
 
 out_unlock:
         current->in_execve = 0;
-        mutex_unlock(&current->cred_exec_mutex);
+        mutex_unlock(&current->cred_guard_mutex);
 
 out_free:
         free_bprm(bprm);
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index d87247d2641f..7f54ba942429 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -145,8 +145,8 @@ extern struct cred init_cred;
         .group_leader   = &tsk,                                         \
         .real_cred      = &init_cred,                                   \
         .cred           = &init_cred,                                   \
-        .cred_exec_mutex =                                              \
-                 __MUTEX_INITIALIZER(tsk.cred_exec_mutex),              \
+        .cred_guard_mutex =                                             \
+                 __MUTEX_INITIALIZER(tsk.cred_guard_mutex),             \
         .comm           = "swapper",                                    \
         .thread         = INIT_THREAD,                                  \
         .fs             = &init_fs,                                     \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3fa82b353c98..5932ace22400 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1247,7 +1247,9 @@ struct task_struct {
                                          * credentials (COW) */
         const struct cred *cred;        /* effective (overridable) subjective task
                                          * credentials (COW) */
-        struct mutex cred_exec_mutex;   /* execve vs ptrace cred calculation mutex */
+        struct mutex cred_guard_mutex;  /* guard against foreign influences on
+                                         * credential calculations
+                                         * (notably. ptrace) */
 
         char comm[TASK_COMM_LEN]; /* executable name excluding path
                                      - access with [gs]et_task_comm (which lock
diff --git a/kernel/cred.c b/kernel/cred.c
index 3a039189d707..1bb4d7e5d616 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -167,7 +167,7 @@ EXPORT_SYMBOL(prepare_creds);
 
 /*
  * Prepare credentials for current to perform an execve()
- * - The caller must hold current->cred_exec_mutex
+ * - The caller must hold current->cred_guard_mutex
  */
 struct cred *prepare_exec_creds(void)
 {
@@ -276,7 +276,7 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
         struct cred *new;
         int ret;
 
-        mutex_init(&p->cred_exec_mutex);
+        mutex_init(&p->cred_guard_mutex);
 
         if (
 #ifdef CONFIG_KEYS
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 0692ab5a0d67..27ac80298bfa 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -185,10 +185,11 @@ int ptrace_attach(struct task_struct *task)
         if (same_thread_group(task, current))
                 goto out;
 
-        /* Protect exec's credential calculations against our interference;
-         * SUID, SGID and LSM creds get determined differently under ptrace.
+        /* Protect the target's credential calculations against our
+         * interference; SUID, SGID and LSM creds get determined differently
+         * under ptrace.
          */
-        retval = mutex_lock_interruptible(&task->cred_exec_mutex);
+        retval = mutex_lock_interruptible(&task->cred_guard_mutex);
         if (retval  < 0)
                 goto out;
 
@@ -232,7 +233,7 @@ repeat:
 bad:
         write_unlock_irqrestore(&tasklist_lock, flags);
         task_unlock(task);
-        mutex_unlock(&task->cred_exec_mutex);
+        mutex_unlock(&task->cred_guard_mutex);
 out:
         return retval;
 }