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Date:   Fri,  2 Sep 2022 03:41:35 +0000
Mime-Version: 1.0
Message-ID: <20220902034135.2853973-1-ovt@google.com>
Subject: [PATCH] seccomp: fix refcounter leak if fork/clone is terminated
From:   Oleksandr Tymoshenko <ovt@google.com>
To:     linux-kernel@vger.kernel.org
Cc:     brauner@kernel.org, Oleksandr Tymoshenko <ovt@google.com>,
        stable@vger.kernel.org
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Precedence: bulk

release_task, where the seccomp's filter refcounter is released, is not
called for the case when the fork/clone is terminated midway by a
signal. This leaves an extra reference that prevents filter from being
destroyed even after all processes using it exit leading to a BPF JIT
memory leak. Dereference the refcounter in the failure path of the
copy_process function.

Fixes: 3a15fb6ed92c ("seccomp: release filter after task is fully dead")
Cc: Christian Brauner <brauner@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Oleksandr Tymoshenko <ovt@google.com>
---
 kernel/fork.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index 90c85b17bf69..20f7a3e91354 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1763,6 +1763,21 @@ static void copy_seccomp(struct task_struct *p)
 #endif
 }
 
+static void release_seccomp(struct task_struct *p)
+{
+#ifdef CONFIG_SECCOMP
+	/*
+	 * Must be called with sighand->lock held, which is common to
+	 * all threads in the group. Holding cred_guard_mutex is not
+	 * needed because this new task is not yet running and cannot
+	 * be racing exec.
+	 */
+	assert_spin_locked(&current->sighand->siglock);
+
+	seccomp_filter_release(p);
+#endif
+}
+
 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
 {
 	current->clear_child_tid = tidptr;
@@ -2495,6 +2510,7 @@ static __latent_entropy struct task_struct *copy_process(
 	return p;
 
 bad_fork_cancel_cgroup:
+	release_seccomp(p);
 	sched_core_free(p);
 	spin_unlock(&current->sighand->siglock);
 	write_unlock_irq(&tasklist_lock);
-- 
2.37.2.789.g6183377224-goog