[PATCH AUTOSEL 5.0 34/66] debugfs: fix use-after-free on symlink traversal

Sasha Levin
2019-04-24T14:35:11Z

From: Al Viro <viro@zeniv.linux.org.uk>

[ Upstream commit 93b919da64c15b90953f96a536e5e61df896ca57 ]

symlink body shouldn't be freed without an RCU delay. Switch debugfs to
->destroy_inode() and use of call_rcu(); free both the inode and symlink
body in the callback. Similar to solution for bpf, only here it's even
more obvious that ->evict_inode() can be dropped.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>
---
fs/debugfs/inode.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 29c68c5d44d5..c4a4fc6f1a95 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -163,19 +163,24 @@ static int debugfs_show_options(struct seq_file *m, struct dentry *root)
return 0;
}

-static void debugfs_evict_inode(struct inode *inode)
+static void debugfs_i_callback(struct rcu_head *head)
{
- truncate_inode_pages_final(&inode->i_data);
- clear_inode(inode);
+ struct inode *inode = container_of(head, struct inode, i_rcu);
if (S_ISLNK(inode->i_mode))
kfree(inode->i_link);
+ free_inode_nonrcu(inode);
+}
+
+static void debugfs_destroy_inode(struct inode *inode)
+{
+ call_rcu(&inode->i_rcu, debugfs_i_callback);
}

static const struct super_operations debugfs_super_operations = {
.statfs = simple_statfs,
.remount_fs = debugfs_remount,
.show_options = debugfs_show_options,
- .evict_inode = debugfs_evict_inode,
+ .destroy_inode = debugfs_destroy_inode,
};

static void debugfs_release_dentry(struct dentry *dentry)
--
2.19.1