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From:   Abhinav Singh <singhabhinav9051571833@gmail.com>
To:     akpm@linux-foundation.org, brauner@kernel.org, surenb@google.com,
        mst@redhat.com, michael.christie@oracle.com,
        mathieu.desnoyers@efficios.com, mjguzik@gmail.com,
        npiggin@gmail.com, shakeelb@google.com, peterz@infradead.org
Cc:     linux-kernel@vger.kernel.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        Abhinav Singh <singhabhinav9051571833@gmail.com>
Subject: [PATCH] Fixing warning of directly dereferencing  __rcu tagged
Date:   Thu, 26 Oct 2023 03:58:11 +0530
Message-Id: <20231025222811.855336-1-singhabhinav9051571833@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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. 
Like normal pointer there should be a check for null case when 
further dereferencing the returned dereferenced __rcu pointer.


Signed-off-by: Abhinav Singh <singhabhinav9051571833@gmail.com>
---
 kernel/fork.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 10917c3e1f03..5afb1b389a66 100644
--- 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;
 	}
-- 
2.39.2