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path: root/fs/overlayfs/namei.c
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Diffstat (limited to 'fs/overlayfs/namei.c')
-rw-r--r--fs/overlayfs/namei.c108
1 files changed, 68 insertions, 40 deletions
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index bf722daf19a9..2043f0369059 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -16,6 +16,7 @@
struct ovl_lookup_data {
struct super_block *sb;
+ struct dentry *dentry;
const struct ovl_layer *layer;
struct qstr name;
bool is_dir;
@@ -24,6 +25,7 @@ struct ovl_lookup_data {
bool stop;
bool last;
char *redirect;
+ char *upperredirect;
int metacopy;
/* Referring to last redirect xattr */
bool absolute_redirect;
@@ -1024,6 +1026,31 @@ int ovl_verify_lowerdata(struct dentry *dentry)
return ovl_maybe_validate_verity(dentry);
}
+/*
+ * Following redirects/metacopy can have security consequences: it's like a
+ * symlink into the lower layer without the permission checks.
+ *
+ * This is only a problem if the upper layer is untrusted (e.g comes from an USB
+ * drive). This can allow a non-readable file or directory to become readable.
+ *
+ * Only following redirects when redirects are enabled disables this attack
+ * vector when not necessary.
+ */
+static bool ovl_check_follow_redirect(struct ovl_lookup_data *d)
+{
+ struct ovl_fs *ofs = OVL_FS(d->sb);
+
+ if (d->metacopy && !ofs->config.metacopy) {
+ pr_warn_ratelimited("refusing to follow metacopy origin for (%pd2)\n", d->dentry);
+ return false;
+ }
+ if ((d->redirect || d->upperredirect) && !ovl_redirect_follow(ofs)) {
+ pr_warn_ratelimited("refusing to follow redirect for (%pd2)\n", d->dentry);
+ return false;
+ }
+ return true;
+}
+
struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
unsigned int flags)
{
@@ -1039,7 +1066,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
unsigned int ctr = 0;
struct inode *inode = NULL;
bool upperopaque = false;
- char *upperredirect = NULL;
+ bool check_redirect = (ovl_redirect_follow(ofs) || ofs->numdatalayer);
struct dentry *this;
unsigned int i;
int err;
@@ -1047,12 +1074,14 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
int metacopy_size = 0;
struct ovl_lookup_data d = {
.sb = dentry->d_sb,
+ .dentry = dentry,
.name = dentry->d_name,
.is_dir = false,
.opaque = false,
.stop = false,
- .last = ovl_redirect_follow(ofs) ? false : !ovl_numlower(poe),
+ .last = check_redirect ? false : !ovl_numlower(poe),
.redirect = NULL,
+ .upperredirect = NULL,
.metacopy = 0,
};
@@ -1094,8 +1123,8 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
if (d.redirect) {
err = -ENOMEM;
- upperredirect = kstrdup(d.redirect, GFP_KERNEL);
- if (!upperredirect)
+ d.upperredirect = kstrdup(d.redirect, GFP_KERNEL);
+ if (!d.upperredirect)
goto out_put_upper;
if (d.redirect[0] == '/')
poe = roe;
@@ -1113,7 +1142,12 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
for (i = 0; !d.stop && i < ovl_numlower(poe); i++) {
struct ovl_path lower = ovl_lowerstack(poe)[i];
- if (!ovl_redirect_follow(ofs))
+ if (!ovl_check_follow_redirect(&d)) {
+ err = -EPERM;
+ goto out_put;
+ }
+
+ if (!check_redirect)
d.last = i == ovl_numlower(poe) - 1;
else if (d.is_dir || !ofs->numdatalayer)
d.last = lower.layer->idx == ovl_numlower(roe);
@@ -1126,13 +1160,6 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
if (!this)
continue;
- if ((uppermetacopy || d.metacopy) && !ofs->config.metacopy) {
- dput(this);
- err = -EPERM;
- pr_warn_ratelimited("refusing to follow metacopy origin for (%pd2)\n", dentry);
- goto out_put;
- }
-
/*
* If no origin fh is stored in upper of a merge dir, store fh
* of lower dir and set upper parent "impure".
@@ -1185,23 +1212,6 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
ctr++;
}
- /*
- * Following redirects can have security consequences: it's like
- * a symlink into the lower layer without the permission checks.
- * This is only a problem if the upper layer is untrusted (e.g
- * comes from an USB drive). This can allow a non-readable file
- * or directory to become readable.
- *
- * Only following redirects when redirects are enabled disables
- * this attack vector when not necessary.
- */
- err = -EPERM;
- if (d.redirect && !ovl_redirect_follow(ofs)) {
- pr_warn_ratelimited("refusing to follow redirect for (%pd2)\n",
- dentry);
- goto out_put;
- }
-
if (d.stop)
break;
@@ -1212,10 +1222,16 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
}
}
- /* Defer lookup of lowerdata in data-only layers to first access */
+ /*
+ * Defer lookup of lowerdata in data-only layers to first access.
+ * Don't require redirect=follow and metacopy=on in this case.
+ */
if (d.metacopy && ctr && ofs->numdatalayer && d.absolute_redirect) {
d.metacopy = 0;
ctr++;
+ } else if (!ovl_check_follow_redirect(&d)) {
+ err = -EPERM;
+ goto out_put;
}
/*
@@ -1298,20 +1314,26 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
/*
* It's safe to assign upperredirect here: the previous
- * assignment of happens only if upperdentry is non-NULL, and
+ * assignment happens only if upperdentry is non-NULL, and
* this one only if upperdentry is NULL.
*/
- upperredirect = ovl_get_redirect_xattr(ofs, &upperpath, 0);
- if (IS_ERR(upperredirect)) {
- err = PTR_ERR(upperredirect);
- upperredirect = NULL;
+ d.upperredirect = ovl_get_redirect_xattr(ofs, &upperpath, 0);
+ if (IS_ERR(d.upperredirect)) {
+ err = PTR_ERR(d.upperredirect);
+ d.upperredirect = NULL;
goto out_free_oe;
}
+
err = ovl_check_metacopy_xattr(ofs, &upperpath, NULL);
if (err < 0)
goto out_free_oe;
- uppermetacopy = err;
+ d.metacopy = uppermetacopy = err;
metacopy_size = err;
+
+ if (!ovl_check_follow_redirect(&d)) {
+ err = -EPERM;
+ goto out_free_oe;
+ }
}
if (upperdentry || ctr) {
@@ -1319,7 +1341,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
.upperdentry = upperdentry,
.oe = oe,
.index = index,
- .redirect = upperredirect,
+ .redirect = d.upperredirect,
};
/* Store lowerdata redirect for lazy lookup */
@@ -1361,7 +1383,7 @@ out_put_upper:
kfree(origin_path);
}
dput(upperdentry);
- kfree(upperredirect);
+ kfree(d.upperredirect);
out:
kfree(d.redirect);
ovl_revert_creds(old_cred);
@@ -1371,7 +1393,7 @@ out:
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 +1416,15 @@ 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:
generated by cgit (git 2.34.1) at 2025-06-19 18:01:51 +0000