2018-11-24 09:25:37

by Pan Bian

Subject: [PATCH] namei: free new_dentry late

After calling dput(new_dentry), new_dentry is passed to fsnotify_move.
This may result in a use-after-free bug. This patch moves the put
operation late.

Fixes: 49d31c2f389a("dentry name snapshots")
Signed-off-by: Pan Bian <[email protected]>
---
fs/namei.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index 0cab649..8b104d9 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4498,7 +4498,6 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
unlock_two_nondirectories(source, target);
else if (target)
inode_unlock(target);
- dput(new_dentry);
if (!error) {
fsnotify_move(old_dir, new_dir, old_name.name, is_dir,
!(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);
@@ -4507,6 +4506,7 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
new_is_dir, NULL, new_dentry);
}
}
+ dput(new_dentry);
release_dentry_name_snapshot(&old_name);

return error;
--
2.7.4

2018-11-24 19:52:09

by Al Viro

Subject: Re: [PATCH] namei: free new_dentry late

On Sat, Nov 24, 2018 at 05:23:24PM +0800, Pan Bian wrote:
> After calling dput(new_dentry), new_dentry is passed to fsnotify_move.
> This may result in a use-after-free bug. This patch moves the put
> operation late.
>
> Fixes: 49d31c2f389a("dentry name snapshots")

What does that commit have to do with anything? The broken part is
fsnotify_move(new_dir, old_dir, old_dentry->d_name.name,
new_is_dir, NULL, new_dentry);
and it predates that commit by 3 years - it came from da1ce0670c14 ("vfs: add
cross-rename")...