Yama: access task_struct->comm directly

The core ptrace access checking routine holds a task lock, and when
reporting a failure, Yama takes a separate task lock. To avoid a
potential deadlock with two ptracers taking the opposite locks, do not
use get_task_comm() and just use ->comm directly since accuracy is not
important for the report.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Suggested-by: Oleg Nesterov <oleg@redhat.com>
CC: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>

1 files changed, 2 insertions, 8 deletions

diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index d51b7c76c37d..0cc99a3ea42d 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -279,12 +279,9 @@ static int yama_ptrace_access_check(struct task_struct *child,
         }
 
         if (rc) {
-                char name[sizeof(current->comm)];
                 printk_ratelimited(KERN_NOTICE
                         "ptrace of pid %d was attempted by: %s (pid %d)\n",
-                        child->pid,
-                        get_task_comm(name, current),
-                        current->pid);
+                        child->pid, current->comm, current->pid);
         }
 
         return rc;
@@ -319,12 +316,9 @@ static int yama_ptrace_traceme(struct task_struct *parent)
         }
 
         if (rc) {
-                char name[sizeof(current->comm)];
                 printk_ratelimited(KERN_NOTICE
                         "ptraceme of pid %d was attempted by: %s (pid %d)\n",
-                        current->pid,
-                        get_task_comm(name, parent),
-                        parent->pid);
+                        current->pid, parent->comm, parent->pid);
         }
 
         return rc;