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ovl: fix regression caused by lookup helpers API changes

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The lookup helpers API was changed by merge of vfs-6.16-rc1.async.dir to
pass a non-const qstr pointer argument to lookup_one*() helpers.

All of the callers of this API were changed to pass a pointer to temp
copy of qstr, except overlays that was passing a const pointer to
dentry->d_name that was changed to pass a non-const copy instead
when doing a lookup in lower layer which is not the fs of said dentry.

This wrong use of the API caused a regression in fstest overlay/012.

Fix the regression by making a non-const copy of dentry->d_name prior
to calling the lookup API, but the API should be fixed to not allow this
class of bugs.

Cc: NeilBrown <neilb@suse.de>
Fixes: 5741909697 ("VFS: improve interface for lookup_one functions")
Fixes: 390e34bc14 ("VFS: change lookup_one_common and lookup_noperm_common to take a qstr")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/20250605101530.2336320-1-amir73il@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Amir Goldstein
2025-06-05 12:15:30 +02:00
committed by Christian Brauner
parent b55eb6eb2a
commit 714d02b419
1 changed files with 8 additions and 2 deletions
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10
fs/overlayfs/namei.c
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@@ -1371,7 +1371,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
bool ovl_lower_positive(struct dentry *dentry)
{
struct ovl_entry *poe = OVL_E(dentry->d_parent);
struct qstr *name = &dentry->d_name;
const struct qstr *name = &dentry->d_name;
const struct cred *old_cred;
unsigned int i;
bool positive = false;
@@ -1394,9 +1394,15 @@ bool ovl_lower_positive(struct dentry *dentry)
struct dentry *this;
struct ovl_path *parentpath = &ovl_lowerstack(poe)[i];
/*
* We need to make a non-const copy of dentry->d_name,
* because lookup_one_positive_unlocked() will hash name
* with parentpath base, which is on another (lower fs).
*/
this = lookup_one_positive_unlocked(
mnt_idmap(parentpath->layer->mnt),
name, parentpath->dentry);
&QSTR_LEN(name->name, name->len),
parentpath->dentry);
if (IS_ERR(this)) {
switch (PTR_ERR(this)) {
case -ENOENT: