From: Sahitya Tummala <stummala@codeaurora.org>
To: Junxiao Bi <junxiao.bi@oracle.com>,
Joel Becker <jlbec@evilplan.org>, Christoph Hellwig <hch@lst.de>,
Al Viro <viro@ZenIV.linux.org.uk>,
linux-kernel@vger.kernel.org
Cc: Sahitya Tummala <stummala@codeaurora.org>
Subject: [PATCH v2] configfs: Fix use-after-free when accessing sd->s_dentry
Date: Thu, 3 Jan 2019 16:48:15 +0530 [thread overview]
Message-ID: <1546514295-24818-1-git-send-email-stummala@codeaurora.org> (raw)
In the vfs_statx() context, during path lookup, the dentry gets
added to sd->s_dentry via configfs_attach_attr(). In the end,
vfs_statx() kills the dentry by calling path_put(), which invokes
configfs_d_iput(). Ideally, this dentry must be removed from
sd->s_dentry but it doesn't if the sd->s_count >= 3. As a result,
sd->s_dentry is holding reference to a stale dentry pointer whose
memory is already freed up. This results in use-after-free issue,
when this stale sd->s_dentry is accessed later in
configfs_readdir() path.
This issue can be easily reproduced, by running the LTP test case -
sh fs_racer_file_list.sh /config
(https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/fs/racer/fs_racer_file_list.sh)
Fixes: 76ae281f6307 ('configfs: fix race between dentry put and lookup')
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
---
v2:
- update comments relevant to the code.
fs/configfs/dir.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 39843fa..f113101 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -58,15 +58,14 @@ static void configfs_d_iput(struct dentry * dentry,
if (sd) {
/* Coordinate with configfs_readdir */
spin_lock(&configfs_dirent_lock);
- /* Coordinate with configfs_attach_attr where will increase
- * sd->s_count and update sd->s_dentry to new allocated one.
- * Only set sd->dentry to null when this dentry is the only
- * sd owner.
+ /*
+ * Set sd->s_dentry to null only when this dentry is the
+ * one that is going to be killed.
* If not do so, configfs_d_iput may run just after
* configfs_attach_attr and set sd->s_dentry to null
* even it's still in use.
*/
- if (atomic_read(&sd->s_count) <= 2)
+ if (sd->s_dentry == dentry)
sd->s_dentry = NULL;
spin_unlock(&configfs_dirent_lock);
--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
next reply other threads:[~2019-01-03 11:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-03 11:18 Sahitya Tummala [this message]
2019-01-31 3:20 ` [PATCH v2] configfs: Fix use-after-free when accessing sd->s_dentry Sahitya Tummala
2019-05-16 12:57 ` stummala
2019-05-17 8:23 ` Christoph Hellwig
2019-05-23 3:49 ` Sahitya Tummala
2019-05-28 6:11 ` Christoph Hellwig
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