linux-kernel - Re: [syzbot] [perf?] KASAN: slab-use-after-free Read in __task_pid_nr

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Message-Id: <20260105023842.1739283-1-wangqing7171@gmail.com>
Date: Mon,  5 Jan 2026 10:38:42 +0800
From: Qing Wang <wangqing7171@...il.com>
To: syzbot+e0378d4f4fe57aa2bdd0@...kaller.appspotmail.com
Cc: acme@...nel.org,
	adrian.hunter@...el.com,
	alexander.shishkin@...ux.intel.com,
	irogers@...gle.com,
	jolsa@...nel.org,
	kan.liang@...ux.intel.com,
	linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	mark.rutland@....com,
	mingo@...hat.com,
	namhyung@...nel.org,
	netdev@...r.kernel.org,
	peterz@...radead.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [perf?] KASAN: slab-use-after-free Read in __task_pid_nr_ns

#syz test

diff --git a/kernel/fork.c b/kernel/fork.c
index b1f3915d5f8e..72b9b37a96c8 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1975,6 +1975,7 @@ __latent_entropy struct task_struct *copy_process(
 	struct file *pidfile = NULL;
 	const u64 clone_flags = args->flags;
 	struct nsproxy *nsp = current->nsproxy;
+	struct signal_struct *free_sig = NULL;
 
 	/*
 	 * Don't allow sharing the root directory with processes in a different
@@ -2501,8 +2502,11 @@ __latent_entropy struct task_struct *copy_process(
 		mmput(p->mm);
 	}
 bad_fork_cleanup_signal:
-	if (!(clone_flags & CLONE_THREAD))
-		free_signal_struct(p->signal);
+	if (!(clone_flags & CLONE_THREAD)) {
+		free_sig = p->signal;
+		p->signal = NULL;
+		free_signal_struct(free_sig);
+	}
 bad_fork_cleanup_sighand:
 	__cleanup_sighand(p->sighand);
 bad_fork_cleanup_fs:
diff --git a/kernel/pid.c b/kernel/pid.c
index a31771bc89c1..1a012e033552 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -329,9 +329,9 @@ EXPORT_SYMBOL_GPL(find_vpid);
 
 static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
 {
-	return (type == PIDTYPE_PID) ?
-		&task->thread_pid :
-		&task->signal->pids[type];
+	if (type == PIDTYPE_PID)
+		return &task->thread_pid;
+	return task->signal ? &task->signal->pids[type] : NULL;
 }
 
 /*
-- 
2.34.1