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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, Matthew Wilcox <willy@infradead.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Jeff Moyer <jmoyer@redhat.com>, Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 4.9 09/61] aio: fix spectre gadget in lookup_ioctx
Date:   Thu, 20 Dec 2018 10:18:09 +0100
Message-Id: <20181220085844.103038300@linuxfoundation.org>
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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Moyer <jmoyer@redhat.com>

commit a538e3ff9dabcdf6c3f477a373c629213d1c3066 upstream.

Matthew pointed out that the ioctx_table is susceptible to spectre v1,
because the index can be controlled by an attacker.  The below patch
should mitigate the attack for all of the aio system calls.

Cc: stable@vger.kernel.org
Reported-by: Matthew Wilcox <willy@infradead.org>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/aio.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/aio.c
+++ b/fs/aio.c
@@ -40,6 +40,7 @@
 #include <linux/ramfs.h>
 #include <linux/percpu-refcount.h>
 #include <linux/mount.h>
+#include <linux/nospec.h>
 
 #include <asm/kmap_types.h>
 #include <asm/uaccess.h>
@@ -1071,6 +1072,7 @@ static struct kioctx *lookup_ioctx(unsig
 	if (!table || id >= table->nr)
 		goto out;
 
+	id = array_index_nospec(id, table->nr);
 	ctx = rcu_dereference(table->table[id]);
 	if (ctx && ctx->user_id == ctx_id) {
 		if (percpu_ref_tryget_live(&ctx->users))