On Thu, 26 Oct 2023 03:58:11 +0530 Abhinav Singh <singhabhinav9051571833@xxxxxxxxx> wrote:
This patch fixes the warning about directly dereferencing a pointer
tagged with __rcu annotation.
Dereferencing the pointers tagged with __rcu directly should
always be avoided according to the docs. There is a rcu helper
functions rcu_dereference(...) to use when dereferencing a __rcu
pointer. This functions returns the non __rcu tagged pointer.
Seems sensible.
Like normal pointer there should be a check for null case when
further dereferencing the returned dereferenced __rcu pointer.
Why is this?
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2369,7 +2369,9 @@ __latent_entropy struct task_struct *copy_process(
retval = -EAGAIN;
if (is_rlimit_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
- if (p->real_cred->user != INIT_USER &&
+ const struct cred *real_cred = rcu_dereference(p->real_cred);
+
+ if (real_cred && real_cred->user != INIT_USER &&
!capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
goto bad_fork_cleanup_count;
The old code assumes that p->read_cred cannot be NULL and the new code
does nothing to make it possible that `real_cred' can be NULL?
In other words, I see no reason to add this new check for NULL?