linux-kernel - [PATCH] Smack: Handle io_uring kernel thread privileges.

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Date:   Thu, 17 Dec 2020 17:12:29 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     "SMACK-discuss@...ts.01.org" <SMACK-discuss@...ts.01.org>,
        Linux Security Module list 
        <linux-security-module@...r.kernel.org>
Cc:     Jens Axboe <axboe@...nel.dk>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] Smack: Handle io_uring kernel thread privileges.

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@...nel.dk>
Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
---
 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 efe2406a3960..7eabb448acab 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());