linux-kernel - [PATCH 4.19 09/44] aio: fix spectre gadget in lookup

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Date:   Tue, 18 Dec 2018 17:39:21 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Jeff Moyer <jmoyer@...hat.com>, Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 4.19 09/44] aio: fix spectre gadget in lookup_ioctx

4.19-stable review patch.  If anyone has any objections, please let me know.

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

From: Jeff Moyer <jmoyer@...hat.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@...r.kernel.org
Reported-by: Matthew Wilcox <willy@...radead.org>
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Jeff Moyer <jmoyer@...hat.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/fs/aio.c
+++ b/fs/aio.c
@@ -45,6 +45,7 @@
 
 #include <asm/kmap_types.h>
 #include <linux/uaccess.h>
+#include <linux/nospec.h>
 
 #include "internal.h"
 
@@ -1038,6 +1039,7 @@ 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))