Date:   Mon, 15 Nov 2021 17:38:50 +0000
Message-Id: <20211115173850.3598768-1-adelva@google.com>
Mime-Version: 1.0
Subject: [PATCH] block: Check ADMIN before NICE for IOPRIO_CLASS_RT
From:   Alistair Delva <adelva@google.com>
To:     linux-kernel@vger.kernel.org
Cc:     Khazhismel Kumykov <khazhy@google.com>,
        Bart Van Assche <bvanassche@acm.org>,
        Serge Hallyn <serge@hallyn.com>, Jens Axboe <axboe@kernel.dk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Paul Moore <paul@paul-moore.com>, selinux@vger.kernel.org,
        linux-security-module@vger.kernel.org, kernel-team@android.com,
        stable@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Booting to Android userspace on 5.14 or newer triggers the following
SELinux denial:

avc: denied { sys_nice } for comm="init" capability=23
     scontext=u:r:init:s0 tcontext=u:r:init:s0 tclass=capability
     permissive=0

Init is PID 0 running as root, so it already has CAP_SYS_ADMIN. For
better compatibility with older SEPolicy, check ADMIN before NICE.

Fixes: 9d3a39a5f1e4 ("block: grant IOPRIO_CLASS_RT to CAP_SYS_NICE")
Signed-off-by: Alistair Delva <adelva@google.com>
Cc: Khazhismel Kumykov <khazhy@google.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Serge Hallyn <serge@hallyn.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: selinux@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
Cc: kernel-team@android.com
Cc: stable@vger.kernel.org # v5.14+
---
 block/ioprio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/ioprio.c b/block/ioprio.c
index 0e4ff245f2bf..4d59c559e057 100644
--- a/block/ioprio.c
+++ b/block/ioprio.c
@@ -69,7 +69,7 @@ int ioprio_check_cap(int ioprio)
 
 	switch (class) {
 		case IOPRIO_CLASS_RT:
-			if (!capable(CAP_SYS_NICE) && !capable(CAP_SYS_ADMIN))
+			if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE))
 				return -EPERM;
 			fallthrough;
 			/* rt has prio field too */
-- 
2.34.0.rc1.387.gb447b232ab-goog