[PATCH 3.16 154/328] fs/quota: Fix spectre gadget in do_quotactl

Ben Hutchings
2018-12-09T22:14:21Z

From: Jeremy Cline <jcline@redhat.com>

commit 7b6924d94a60c6b8c1279ca003e8744e6cd9e8b1 upstream.

'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>
Signed-off-by: Jeremy Cline <jcline@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
[bwh: Backported to 3.16: The maximum valid quota type is command-dependent.
Introduce a local variable rather than repeating the expression.]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/fs/quota/quota.c
+++ b/fs/quota/quota.c
@@ -17,6 +17,7 @@
#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)
@@ -405,10 +406,12 @@ static int quota_rmxquota(struct super_b
static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
void __user *addr, struct path *path)
{
+ unsigned int max_quotas = XQM_COMMAND(cmd) ? XQM_MAXQUOTAS : MAXQUOTAS;
int ret;

- if (type >= (XQM_COMMAND(cmd) ? XQM_MAXQUOTAS : MAXQUOTAS))
+ if (type >= max_quotas)
return -EINVAL;
+ type = array_index_nospec(type, max_quotas);
if (!sb->s_qcop)
return -ENOSYS;