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ovl: add ovl_override_creator_creds cred guard

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The current code to override credentials for creation operations is
pretty difficult to understand. We effectively override the credentials
twice:

(1) override with the mounter's credentials
(2) copy the mounts credentials and override the fs{g,u}id with the inode {u,g}id

And then we elide the revert because it would be an idempotent revert.
That elision doesn't buy us anything anymore though because I've made it
all work without any reference counting anyway. All it does is mix the
two credential overrides together.

We can use a cleanup guard to clarify the creation codepaths and make
them easier to understand.

This just introduces the cleanup guard keeping the patch reviewable.
We'll convert the caller in follow-up patches and then drop the
duplicated code.

Link: https://patch.msgid.link/20251117-work-ovl-cred-guard-prepare-v2-1-bd1c97a36d7b@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner
2025-11-17 10:34:38 +01:00
parent 5c06bc9f06
commit f37b334728
1 changed files with 36 additions and 0 deletions
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36
fs/overlayfs/dir.c
View File

@@ -581,6 +581,42 @@ out_cleanup_unlocked:
goto out_dput;
}
static const struct cred *ovl_override_creator_creds(struct dentry *dentry, struct inode *inode, umode_t mode)
{
int err;
if (WARN_ON_ONCE(current->cred != ovl_creds(dentry->d_sb)))
return ERR_PTR(-EINVAL);
CLASS(prepare_creds, override_cred)();
if (!override_cred)
return ERR_PTR(-ENOMEM);
override_cred->fsuid = inode->i_uid;
override_cred->fsgid = inode->i_gid;
err = security_dentry_create_files_as(dentry, mode, &dentry->d_name,
current->cred, override_cred);
if (err)
return ERR_PTR(err);
return override_creds(no_free_ptr(override_cred));
}
static void ovl_revert_creator_creds(const struct cred *old_cred)
{
const struct cred *override_cred;
override_cred = revert_creds(old_cred);
put_cred(override_cred);
}
DEFINE_CLASS(ovl_override_creator_creds,
const struct cred *,
if (!IS_ERR_OR_NULL(_T)) ovl_revert_creator_creds(_T),
ovl_override_creator_creds(dentry, inode, mode),
struct dentry *dentry, struct inode *inode, umode_t mode)
static const struct cred *ovl_setup_cred_for_create(struct dentry *dentry,
struct inode *inode,
umode_t mode,