linux-kernel - [PATCH] proc: revalidate kernel thread inodes to root:root

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Message-ID: <20180412220109.GA20978@avx2>
Date:   Fri, 13 Apr 2018 01:01:09 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, ebiederm@...ssion.com
Subject: [PATCH] proc: revalidate kernel thread inodes to root:root

task_dump_owner() has the following code:

	mm = task->mm;
	if (mm) {
		if (get_dumpable(mm) != SUID_DUMP_USER) {
			uid = ...
		}
	}

Check for ->mm is buggy -- kernel thread might be borrowing mm
and inode will go to some random uid:gid pair.

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 fs/proc/base.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1693,6 +1693,12 @@ void task_dump_owner(struct task_struct *task, umode_t mode,
 	kuid_t uid;
 	kgid_t gid;
 
+	if (unlikely(task->flags & PF_KTHREAD)) {
+		*ruid = GLOBAL_ROOT_UID;
+		*rgid = GLOBAL_ROOT_GID;
+		return;
+	}
+
 	/* Default to the tasks effective ownership */
 	rcu_read_lock();
 	cred = __task_cred(task);