[ 21/46] Yama: access task_struct->comm directly

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg KH <gregkh@linuxfoundation.org>

3.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@chromium.org>

commit 7612bfeecc197bbb6629842b5c6ff1967f0a9b70 upstream.

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>
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 security/yama/yama_lsm.c |   10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -279,12 +279,9 @@ static int yama_ptrace_access_check(stru
 	}
 
 	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 ta
 	}
 
 	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;