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: da1ce0670c14("vfs: add cross-rename")
Signed-off-by: Pan Bian <[email protected]>
---
V2: correct the fixes commit information
---
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
On Sun 25-11-18 08:15:23, 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: da1ce0670c14("vfs: add cross-rename")
> Signed-off-by: Pan Bian <[email protected]>
The code is actually fine AFAICT. One new_dentry reference is passed into
vfs_rename() and another one is acquired directly inside vfs_rename(). That
is the one dropped early but there's still the original reference passed in
protecting new_dentry from freeing. Am I missing something?
Honza
> ---
> V2: correct the fixes commit information
> ---
> 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
>
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
On Tue 27-11-18 17:57:12, PanBian wrote:
> On Tue, Nov 27, 2018 at 10:25:51AM +0100, Jan Kara wrote:
> > On Sun 25-11-18 08:15:23, 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: da1ce0670c14("vfs: add cross-rename")
> > > Signed-off-by: Pan Bian <[email protected]>
> >
> > The code is actually fine AFAICT. One new_dentry reference is passed into
> > vfs_rename() and another one is acquired directly inside vfs_rename(). That
> > is the one dropped early but there's still the original reference passed in
> > protecting new_dentry from freeing. Am I missing something?
>
> I am not quite sure about the actual execution logic. But I guess new_dentry
> reference may be dropped outside vfs_rename in cocurrent executions.
> Otherwise, there is no need to acquire & drop new_dentry reference as it
> is always alive along vfs_rename.
I don't think that's the case. The dget() - dput() pair just looks
superfluous to me in vfs_rename(). Am I missing something Miklos?
Honza
> > > 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
> > >
> > >
> > --
> > Jan Kara <[email protected]>
> > SUSE Labs, CR
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
On Tue, Nov 27, 2018 at 10:25:51AM +0100, Jan Kara wrote:
> On Sun 25-11-18 08:15:23, 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: da1ce0670c14("vfs: add cross-rename")
> > Signed-off-by: Pan Bian <[email protected]>
>
> The code is actually fine AFAICT. One new_dentry reference is passed into
> vfs_rename() and another one is acquired directly inside vfs_rename(). That
> is the one dropped early but there's still the original reference passed in
> protecting new_dentry from freeing. Am I missing something?
I am not quite sure about the actual execution logic. But I guess new_dentry
reference may be dropped outside vfs_rename in cocurrent executions.
Otherwise, there is no need to acquire & drop new_dentry reference as it
is always alive along vfs_rename.
Best regards,
Pan
>
> Honza
>
> > ---
> > V2: correct the fixes commit information
> > ---
> > 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
> >
> >
> --
> Jan Kara <[email protected]>
> SUSE Labs, CR
On Tue, Nov 27, 2018 at 11:05 AM Jan Kara <[email protected]> wrote:
>
> On Tue 27-11-18 17:57:12, PanBian wrote:
> > I am not quite sure about the actual execution logic. But I guess new_dentry
> > reference may be dropped outside vfs_rename in cocurrent executions.
> > Otherwise, there is no need to acquire & drop new_dentry reference as it
> > is always alive along vfs_rename.
>
> I don't think that's the case. The dget() - dput() pair just looks
> superfluous to me in vfs_rename(). Am I missing something Miklos?
I think those are to protect against d_delete() called from fs to
reset d_inode. The caller indeed has to hold one ref anyway.
So not superfluous, but only needed due to d_delete() and not to
protect against freeing of dentry.
Thanks,
Miklos