Commit f6122ed2 authored by Sahitya Tummala's avatar Sahitya Tummala Committed by Christoph Hellwig
Browse files

configfs: Fix use-after-free when accessing sd->s_dentry

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 /config

Fixes: 76ae281f

 ('configfs: fix race between dentry put and lookup')
Signed-off-by: default avatarSahitya Tummala <>
Signed-off-by: default avatarChristoph Hellwig <>
parent cd6c84d8
......@@ -58,15 +58,13 @@ static void configfs_d_iput(struct dentry * dentry,
if (sd) {
/* Coordinate with configfs_readdir */
/* 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.
* 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.
* Set sd->s_dentry to null only when this dentry is the one
* that is going to be killed. Otherwise 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;
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