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aio: fix spectre gadget in lookup_ioctx 

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.

Reported-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Jeff Moyer 2018-12-11 12:37:49 -05:00 committed by Al Viro
parent 73116df7bb
commit 0afa996483
1 changed files with 2 additions and 0 deletions
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2
fs/aio.c
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@ -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(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))