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debugfs: fix use-after-free on symlink traversal

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[ Upstream commit 93b919da64 ]

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 <sashal@kernel.org>
This commit is contained in:
Al Viro 2019-03-26 01:43:37 +00:00 committed by Greg Kroah-Hartman
parent f9c04ee063
commit c49cf5c847
1 changed files with 9 additions and 4 deletions
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13
fs/debugfs/inode.c
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@ -170,19 +170,24 @@ 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 struct vfsmount *debugfs_automount(struct path *path)