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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, Stefan Metzmacher <metze@samba.org>,
        Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 5.4 033/222] io_uring: only allow submit from owning task
Date:   Wed, 22 Jan 2020 10:26:59 +0100
Message-Id: <20200122092835.852416399@linuxfoundation.org>
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From: Jens Axboe <axboe@kernel.dk>

commit 44d282796f81eb1debc1d7cb53245b4cb3214cb5 upstream.

If the credentials or the mm doesn't match, don't allow the task to
submit anything on behalf of this ring. The task that owns the ring can
pass the file descriptor to another task, but we don't want to allow
that task to submit an SQE that then assumes the ring mm and creds if
it needs to go async.

Cc: stable@vger.kernel.org
Suggested-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>


---
 fs/io_uring.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3716,6 +3716,12 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned
 			wake_up(&ctx->sqo_wait);
 		submitted = to_submit;
 	} else if (to_submit) {
+		if (current->mm != ctx->sqo_mm ||
+		    current_cred() != ctx->creds) {
+			ret = -EPERM;
+			goto out;
+		}
+
 		to_submit = min(to_submit, ctx->sq_entries);
 
 		mutex_lock(&ctx->uring_lock);