In 0ee50b47532a ("namei: change filename_parentat() calling
conventions"), filename_parentat() was made to always put the struct
filename before returning, and kern_path_locked() was migrated to this
calling convention. However, kern_path_locked() uses the "last"
parameter to lookup and potentially create a new dentry. The last
parameter contains the last component of the path and points within the
filename, which was recently freed at the end of filename_parentat().
Thus, when kern_path_locked() calls __lookup_hash(), it is using the
filename after it has already been freed.
To avoid this, switch back to __filename_parentat() and place a putname
at the end of the function, once all uses are completed.
Fixes: 0ee50b47532a ("namei: change filename_parentat() calling conventions")
Reported-by: [email protected]
Signed-off-by: Stephen Brennan <[email protected]>
---
fs/namei.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index d049d3972695..a0122f0016a3 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2551,17 +2551,22 @@ static int filename_parentat(int dfd, struct filename *name,
/* does lookup, returns the object with parent locked */
struct dentry *kern_path_locked(const char *name, struct path *path)
{
+ struct filename *filename;
struct dentry *d;
struct qstr last;
int type, error;
- error = filename_parentat(AT_FDCWD, getname_kernel(name), 0, path,
+ filename = getname_kernel(name);
+ error = __filename_parentat(AT_FDCWD, filename, 0, path,
&last, &type);
- if (error)
- return ERR_PTR(error);
+ if (error) {
+ d = ERR_PTR(error);
+ goto out;
+ }
if (unlikely(type != LAST_NORM)) {
path_put(path);
- return ERR_PTR(-EINVAL);
+ d = ERR_PTR(-EINVAL);
+ goto out;
}
inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
d = __lookup_hash(&last, path->dentry, 0);
@@ -2569,6 +2574,8 @@ struct dentry *kern_path_locked(const char *name, struct path *path)
inode_unlock(path->dentry->d_inode);
path_put(path);
}
+out:
+ putname(filename);
return d;
}
--
2.30.2
On Wed, Sep 01, 2021 at 02:35:08PM +0700, Dmitry Kadashev wrote:
> On Wed, Sep 1, 2021 at 7:13 AM Stephen Brennan
> <[email protected]> wrote:
> >
> > In 0ee50b47532a ("namei: change filename_parentat() calling
> > conventions"), filename_parentat() was made to always put the struct
> > filename before returning, and kern_path_locked() was migrated to this
> > calling convention. However, kern_path_locked() uses the "last"
> > parameter to lookup and potentially create a new dentry. The last
> > parameter contains the last component of the path and points within the
> > filename, which was recently freed at the end of filename_parentat().
> > Thus, when kern_path_locked() calls __lookup_hash(), it is using the
> > filename after it has already been freed.
> >
> > To avoid this, switch back to __filename_parentat() and place a putname
> > at the end of the function, once all uses are completed.
>
> Ouch. Thanks for taking care of this, Stephen. I guess
> filename_parentat() should be killed, since kern_path_locked() was the
> only place it's used in and it always results in danging "last",
> provoking bugs just like this one. I can send a patch on top of this if
> you prefer.
Yes. And then rename __filename_parentat to filename_parentat, please.
On Wed, Sep 1, 2021 at 4:13 PM Christoph Hellwig <[email protected]> wrote:
>
> On Wed, Sep 01, 2021 at 02:35:08PM +0700, Dmitry Kadashev wrote:
> > Ouch. Thanks for taking care of this, Stephen. I guess
> > filename_parentat() should be killed, since kern_path_locked() was the
> > only place it's used in and it always results in danging "last",
> > provoking bugs just like this one. I can send a patch on top of this if
> > you prefer.
>
> Yes. And then rename __filename_parentat to filename_parentat, please.
I see why you want it to be renamed - and I'll send the patch. The only
problem I have with the rename is with __filename_parentat() there is a
nice uniformity: filename_* functions consume the passed name, and
__filename_* do not. So maybe it's something nice to have. Maybe not.
Anyway, as I've mentioned, I'll send the patch and it can be either
picked up or ignored.
--
Dmitry
On Wed, Sep 1, 2021 at 7:13 AM Stephen Brennan
<[email protected]> wrote:
>
> In 0ee50b47532a ("namei: change filename_parentat() calling
> conventions"), filename_parentat() was made to always put the struct
> filename before returning, and kern_path_locked() was migrated to this
> calling convention. However, kern_path_locked() uses the "last"
> parameter to lookup and potentially create a new dentry. The last
> parameter contains the last component of the path and points within the
> filename, which was recently freed at the end of filename_parentat().
> Thus, when kern_path_locked() calls __lookup_hash(), it is using the
> filename after it has already been freed.
>
> To avoid this, switch back to __filename_parentat() and place a putname
> at the end of the function, once all uses are completed.
Ouch. Thanks for taking care of this, Stephen. I guess
filename_parentat() should be killed, since kern_path_locked() was the
only place it's used in and it always results in danging "last",
provoking bugs just like this one. I can send a patch on top of this if
you prefer.
--
Dmitry