aio: fix spectre gadget in lookup_ioctx

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>

diff --git a/fs/aio.c b/fs/aio.c
index c283eb03cb38e29fd2b4edb1082eab48c17a2838..7187d03aa0bc8b788680ca49b2a7e39a8b2fd8e8 100644 (file)
--- 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>
@@ -1063,6 +1064,7 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
        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))