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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.10 508/717] Smack: Handle io_uring kernel thread privileges
Date:   Mon, 28 Dec 2020 13:48:26 +0100
Message-Id: <20201228125045.299088799@linuxfoundation.org>
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From: Casey Schaufler <casey@schaufler-ca.com>

[ Upstream commit 942cb357ae7d9249088e3687ee6a00ed2745a0c7 ]

Smack assumes that kernel threads are privileged for smackfs
operations. This was necessary because the credential of the
kernel thread was not related to a user operation. With io_uring
the credential does reflect a user's rights and can be used.

Suggested-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 security/smack/smack_access.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index efe2406a39609..7eabb448acab4 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -688,9 +688,10 @@ bool smack_privileged_cred(int cap, const struct cred *cred)
 bool smack_privileged(int cap)
 {
 	/*
-	 * All kernel tasks are privileged
+	 * Kernel threads may not have credentials we can use.
+	 * The io_uring kernel threads do have reliable credentials.
 	 */
-	if (unlikely(current->flags & PF_KTHREAD))
+	if ((current->flags & (PF_KTHREAD | PF_IO_WORKER)) == PF_KTHREAD)
 		return true;
 
 	return smack_privileged_cred(cap, current_cred());
-- 
2.27.0