linux-kernel - [PATCH] proc: Put thread_pid in release_task not proc_flush

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Date:   Fri, 24 Apr 2020 15:50:20 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Alexey Gladkov <legion@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH] proc: Put thread_pid in release_task not proc_flush_pid


Oleg pointed out that in the unlikely event the kernel is compiled
with CONFIG_PROC_FS unset that release_task will now leak the pid.

Move the put_pid out of proc_flush_pid into release_task to fix this
and to guarantee I don't make that mistake again.

When possible it makes sense to keep get and put in the same function
so it can easily been seen how they pair up.

Fixes: 7bc3e6e55acf ("proc: Use a list of inodes to flush from proc")
Reported-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/proc/base.c | 1 -
 kernel/exit.c  | 1 +
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 6042b646ab27..42f43c7b9669 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3274,7 +3274,6 @@ static const struct inode_operations proc_tgid_base_inode_operations = {
 void proc_flush_pid(struct pid *pid)
 {
 	proc_invalidate_siblings_dcache(&pid->inodes, &pid->lock);
-	put_pid(pid);
 }
 
 static struct dentry *proc_pid_instantiate(struct dentry * dentry,
diff --git a/kernel/exit.c b/kernel/exit.c
index 389a88cb3081..ce2a75bc0ade 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -219,6 +219,7 @@ void release_task(struct task_struct *p)
 
 	write_unlock_irq(&tasklist_lock);
 	proc_flush_pid(thread_pid);
+	put_pid(thread_pid);
 	release_thread(p);
 	put_task_struct_rcu_user(p);
 
-- 
2.20.1