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From:   Jeremy Cline <jcline@redhat.com>
To:     Jan Kara <jack@suse.com>
Cc:     linux-kernel@vger.kernel.org, Josh Poimboeuf <jpoimboe@redhat.com>,
        Jeremy Cline <jcline@redhat.com>, stable@vger.kernel.org
Subject: [PATCH 2/2] fs/quota: Fix spectre gadget in do_quotactl
Date:   Tue, 31 Jul 2018 01:37:31 +0000
Message-Id: <20180731013731.1987-3-jcline@redhat.com>
In-Reply-To: <20180731013731.1987-1-jcline@redhat.com>
References: <20180731013731.1987-1-jcline@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

'type' is user-controlled, so sanitize it after the bounds check to
avoid using it in speculative execution. This covers the following
potential gadgets detected with the help of smatch:

* fs/ext4/super.c:5741 ext4_quota_read() warn: potential spectre issue
  'sb_dqopt(sb)->files' [r]
* fs/ext4/super.c:5778 ext4_quota_write() warn: potential spectre issue
  'sb_dqopt(sb)->files' [r]
* fs/f2fs/super.c:1552 f2fs_quota_read() warn: potential spectre issue
  'sb_dqopt(sb)->files' [r]
* fs/f2fs/super.c:1608 f2fs_quota_write() warn: potential spectre issue
  'sb_dqopt(sb)->files' [r]
* fs/quota/dquot.c:412 mark_info_dirty() warn: potential spectre issue
  'sb_dqopt(sb)->info' [w]
* fs/quota/dquot.c:933 dqinit_needed() warn: potential spectre issue
  'dquots' [r]
* fs/quota/dquot.c:2112 dquot_commit_info() warn: potential spectre
  issue 'dqopt->ops' [r]
* fs/quota/dquot.c:2362 vfs_load_quota_inode() warn: potential spectre
  issue 'dqopt->files' [w] (local cap)
* fs/quota/dquot.c:2369 vfs_load_quota_inode() warn: potential spectre
  issue 'dqopt->ops' [w] (local cap)
* fs/quota/dquot.c:2370 vfs_load_quota_inode() warn: potential spectre
  issue 'dqopt->info' [w] (local cap)
* fs/quota/quota.c:110 quota_getfmt() warn: potential spectre issue
  'sb_dqopt(sb)->info' [r]
* fs/quota/quota_v2.c:84 v2_check_quota_file() warn: potential spectre
  issue 'quota_magics' [w]
* fs/quota/quota_v2.c:85 v2_check_quota_file() warn: potential spectre
  issue 'quota_versions' [w]
* fs/quota/quota_v2.c:96 v2_read_file_info() warn: potential spectre
  issue 'dqopt->info' [r]
* fs/quota/quota_v2.c:172 v2_write_file_info() warn: potential spectre
  issue 'dqopt->info' [r]

Additionally, a quick inspection indicates there are array accesses with
'type' in quota_on() and quota_off() functions which are also addressed
by this.

Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jeremy Cline <jcline@redhat.com>
---

This patch isn't going to cleanly apply to stable without the "fs/quota:
Replace XQM_MAXQUOTAS usage with MAXQUOTAS" patch, but I'm not sure that
patch is really stable material and XQM_MAXQUOTAS has been 3 since
pre-v4.4 so the end result will be the same even if that patch isn't
backported.

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

diff --git a/fs/quota/quota.c b/fs/quota/quota.c
index d403392d8a0f..f0cbf58ad4da 100644
--- a/fs/quota/quota.c
+++ b/fs/quota/quota.c
@@ -18,6 +18,7 @@
 #include <linux/quotaops.h>
 #include <linux/types.h>
 #include <linux/writeback.h>
+#include <linux/nospec.h>
 
 static int check_quotactl_permission(struct super_block *sb, int type, int cmd,
 				     qid_t id)
@@ -701,6 +702,7 @@ static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
 
 	if (type >= MAXQUOTAS)
 		return -EINVAL;
+	type = array_index_nospec(type, MAXQUOTAS);
 	/*
 	 * Quota not supported on this fs? Check this before s_quota_types
 	 * since they needn't be set if quota is not supported at all.
-- 
2.17.1