[PATCH 4.9 09/61] aio: fix spectre gadget in lookup_ioctx

From: Greg Kroah-Hartman
Date: Thu Dec 20 2018 - 04:42:39 EST

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


From: Jeff Moyer <jmoyer@xxxxxxxxxx>

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@xxxxxxxxxxxxxxx
Reported-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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))