Messages in this thread | | | Date | Wed, 25 Oct 2023 15:38:07 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] Fixing warning of directly dereferencing __rcu tagged |
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On Thu, 26 Oct 2023 03:58:11 +0530 Abhinav Singh <singhabhinav9051571833@gmail.com> 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?
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