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ovl: Optimize override/revert creds

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Use override_creds_light() in ovl_override_creds() and
revert_creds_light() in ovl_revert_creds().

The _light() functions do not change the 'usage' of the credentials in
question, as they refer to the credentials associated with the
mounter, which have a longer lifetime.

In ovl_setup_cred_for_create(), do not need to modify the mounter
credentials (returned by override_creds_light()) 'usage' counter.
Add a warning to verify that we are indeed working with the mounter
credentials (stored in the superblock). Failure in this assumption
means that creds may leak.

Suggested-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
This commit is contained in:
Vinicius Costa Gomes 2024-11-14 09:52:23 +01:00 committed by Amir Goldstein
parent 711747e204
commit c5b28fc161
2 changed files with 11 additions and 3 deletions
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10
fs/overlayfs/dir.c
View File

@ -573,7 +573,15 @@ static const struct cred *ovl_setup_cred_for_create(struct dentry *dentry,
put_cred(override_cred);
return ERR_PTR(err);
}
put_cred(override_creds(override_cred));
/*
* Caller is going to match this with revert_creds_light() and drop
* referenec on the returned creds.
* We must be called with creator creds already, otherwise we risk
* leaking creds.
*/
old_cred = override_creds_light(override_cred);
WARN_ON_ONCE(old_cred != ovl_creds(dentry->d_sb));
return override_cred;
}

4
fs/overlayfs/util.c
View File

@ -65,12 +65,12 @@ const struct cred *ovl_override_creds(struct super_block *sb)
{
struct ovl_fs *ofs = OVL_FS(sb);
return override_creds(ofs->creator_cred);
return override_creds_light(ofs->creator_cred);
}
void ovl_revert_creds(const struct cred *old_cred)
{
revert_creds(old_cred);
revert_creds_light(old_cred);
}
/*