audit: get comm using lock to avoid race in string printing

When task->comm is passed directly to audit_log_untrustedstring() without
getting a copy or using the task_lock, there is a race that could happen that
would output a NULL (\0) in the output string that would effectively truncate
the rest of the report text after the comm= field in the audit, losing fields.

Use get_task_comm() to get a copy while acquiring the task_lock to prevent
this and to prevent the result from being a mixture of old and new values of
comm.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/kernel/audit.c b/kernel/audit.c
index 3a80abb6eaa1..53bb39bf79e2 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1850,7 +1850,7 @@ EXPORT_SYMBOL(audit_log_task_context);
 void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
 {
         const struct cred *cred;
-        char name[sizeof(tsk->comm)];
+        char comm[sizeof(tsk->comm)];
         struct mm_struct *mm = tsk->mm;
         char *tty;
 
@@ -1884,9 +1884,8 @@ void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
                          from_kgid(&init_user_ns, cred->fsgid),
                          tty, audit_get_sessionid(tsk));
 
-        get_task_comm(name, tsk);
         audit_log_format(ab, " comm=");
-        audit_log_untrustedstring(ab, name);
+        audit_log_untrustedstring(ab, get_task_comm(comm, tsk));
 
         if (mm) {
                 down_read(&mm->mmap_sem);