yama: don't abuse rcu_read_lock/get_task_struct in yama_task_prctl()

current->group_leader is stable, no need to take rcu_read_lock() and do
get/put_task_struct().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20250219161417.GA20851@redhat.com
Signed-off-by: Kees Cook <kees@kernel.org>

diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index 1971710620c184dc9d3f8078902ddc7d2ef2f523..3d064dd4e03f9eaaf5258b37ad05641b35967995 100644 (file)
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -222,7 +222,7 @@ static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
                           unsigned long arg4, unsigned long arg5)
 {
        int rc = -ENOSYS;
-       struct task_struct *myself = current;
+       struct task_struct *myself;
 
        switch (option) {
        case PR_SET_PTRACER:
@@ -232,11 +232,7 @@ static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
                 * leader checking is handled later when walking the ancestry
                 * at the time of PTRACE_ATTACH check.
                 */
-               rcu_read_lock();
-               if (!thread_group_leader(myself))
-                       myself = rcu_dereference(myself->group_leader);
-               get_task_struct(myself);
-               rcu_read_unlock();
+               myself = current->group_leader;
 
                if (arg2 == 0) {
                        yama_ptracer_del(NULL, myself);
@@ -255,7 +251,6 @@ static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
                        }
                }
 
-               put_task_struct(myself);
                break;
        }