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|
/*
* Copyright (C) 2011 Novell Inc.
* Copyright (C) 2016 Red Hat, Inc.
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 as published by
* the Free Software Foundation.
*/
#include <linux/fs.h>
#include <linux/cred.h>
#include <linux/namei.h>
#include <linux/xattr.h>
#include <linux/ratelimit.h>
#include <linux/mount.h>
#include <linux/exportfs.h>
#include "overlayfs.h"
struct ovl_lookup_data {
struct qstr name;
bool is_dir;
bool opaque;
bool stop;
bool last;
char *redirect;
};
static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
size_t prelen, const char *post)
{
int res;
char *s, *next, *buf = NULL;
res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, NULL, 0);
if (res < 0) {
if (res == -ENODATA || res == -EOPNOTSUPP)
return 0;
goto fail;
}
buf = kzalloc(prelen + res + strlen(post) + 1, GFP_KERNEL);
if (!buf)
return -ENOMEM;
if (res == 0)
goto invalid;
res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, buf, res);
if (res < 0)
goto fail;
if (res == 0)
goto invalid;
if (buf[0] == '/') {
for (s = buf; *s++ == '/'; s = next) {
next = strchrnul(s, '/');
if (s == next)
goto invalid;
}
} else {
if (strchr(buf, '/') != NULL)
goto invalid;
memmove(buf + prelen, buf, res);
memcpy(buf, d->name.name, prelen);
}
strcat(buf, post);
kfree(d->redirect);
d->redirect = buf;
d->name.name = d->redirect;
d->name.len = strlen(d->redirect);
return 0;
err_free:
kfree(buf);
return 0;
fail:
pr_warn_ratelimited("overlayfs: failed to get redirect (%i)\n", res);
goto err_free;
invalid:
pr_warn_ratelimited("overlayfs: invalid redirect (%s)\n", buf);
goto err_free;
}
static int ovl_acceptable(void *ctx, struct dentry *dentry)
{
return 1;
}
static struct ovl_fh *ovl_get_origin_fh(struct dentry *dentry)
{
int res;
struct ovl_fh *fh = NULL;
res = vfs_getxattr(dentry, OVL_XATTR_ORIGIN, NULL, 0);
if (res < 0) {
if (res == -ENODATA || res == -EOPNOTSUPP)
return NULL;
goto fail;
}
/* Zero size value means "copied up but origin unknown" */
if (res == 0)
return NULL;
fh = kzalloc(res, GFP_KERNEL);
if (!fh)
return ERR_PTR(-ENOMEM);
res = vfs_getxattr(dentry, OVL_XATTR_ORIGIN, fh, res);
if (res < 0)
goto fail;
if (res < sizeof(struct ovl_fh) || res < fh->len)
goto invalid;
if (fh->magic != OVL_FH_MAGIC)
goto invalid;
/* Treat larger version and unknown flags as "origin unknown" */
if (fh->version > OVL_FH_VERSION || fh->flags & ~OVL_FH_FLAG_ALL)
goto out;
/* Treat endianness mismatch as "origin unknown" */
if (!(fh->flags & OVL_FH_FLAG_ANY_ENDIAN) &&
(fh->flags & OVL_FH_FLAG_BIG_ENDIAN) != OVL_FH_FLAG_CPU_ENDIAN)
goto out;
return fh;
out:
kfree(fh);
return NULL;
fail:
pr_warn_ratelimited("overlayfs: failed to get origin (%i)\n", res);
goto out;
invalid:
pr_warn_ratelimited("overlayfs: invalid origin (%*phN)\n", res, fh);
goto out;
}
static struct dentry *ovl_get_origin(struct dentry *dentry,
struct vfsmount *mnt)
{
struct dentry *origin = NULL;
struct ovl_fh *fh = ovl_get_origin_fh(dentry);
int bytes;
if (IS_ERR_OR_NULL(fh))
return (struct dentry *)fh;
/*
* Make sure that the stored uuid matches the uuid of the lower
* layer where file handle will be decoded.
*/
if (!uuid_equal(&fh->uuid, &mnt->mnt_sb->s_uuid))
goto out;
bytes = (fh->len - offsetof(struct ovl_fh, fid));
origin = exportfs_decode_fh(mnt, (struct fid *)fh->fid,
bytes >> 2, (int)fh->type,
ovl_acceptable, NULL);
if (IS_ERR(origin)) {
/* Treat stale file handle as "origin unknown" */
if (origin == ERR_PTR(-ESTALE))
origin = NULL;
goto out;
}
if (ovl_dentry_weird(origin) ||
((d_inode(origin)->i_mode ^ d_inode(dentry)->i_mode) & S_IFMT))
goto invalid;
out:
kfree(fh);
return origin;
invalid:
pr_warn_ratelimited("overlayfs: invalid origin (%pd2)\n", origin);
dput(origin);
origin = NULL;
goto out;
}
static bool ovl_is_opaquedir(struct dentry *dentry)
{
return ovl_check_dir_xattr(dentry, OVL_XATTR_OPAQUE);
}
static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
const char *name, unsigned int namelen,
size_t prelen, const char *post,
struct dentry **ret)
{
struct dentry *this;
int err;
this = lookup_one_len_unlocked(name, base, namelen);
if (IS_ERR(this)) {
err = PTR_ERR(this);
this = NULL;
if (err == -ENOENT || err == -ENAMETOOLONG)
goto out;
goto out_err;
}
if (!this->d_inode)
goto put_and_out;
if (ovl_dentry_weird(this)) {
/* Don't support traversing automounts and other weirdness */
err = -EREMOTE;
goto out_err;
}
if (ovl_is_whiteout(this)) {
d->stop = d->opaque = true;
goto put_and_out;
}
if (!d_can_lookup(this)) {
d->stop = true;
if (d->is_dir)
goto put_and_out;
goto out;
}
d->is_dir = true;
if (!d->last && ovl_is_opaquedir(this)) {
d->stop = d->opaque = true;
goto out;
}
err = ovl_check_redirect(this, d, prelen, post);
if (err)
goto out_err;
out:
*ret = this;
return 0;
put_and_out:
dput(this);
this = NULL;
goto out;
out_err:
dput(this);
return err;
}
static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
struct dentry **ret)
{
/* Counting down from the end, since the prefix can change */
size_t rem = d->name.len - 1;
struct dentry *dentry = NULL;
int err;
if (d->name.name[0] != '/')
return ovl_lookup_single(base, d, d->name.name, d->name.len,
0, "", ret);
while (!IS_ERR_OR_NULL(base) && d_can_lookup(base)) {
const char *s = d->name.name + d->name.len - rem;
const char *next = strchrnul(s, '/');
size_t thislen = next - s;
bool end = !next[0];
/* Verify we did not go off the rails */
if (WARN_ON(s[-1] != '/'))
return -EIO;
err = ovl_lookup_single(base, d, s, thislen,
d->name.len - rem, next, &base);
dput(dentry);
if (err)
return err;
dentry = base;
if (end)
break;
rem -= thislen + 1;
if (WARN_ON(rem >= d->name.len))
return -EIO;
}
*ret = dentry;
return 0;
}
static int ovl_check_origin(struct dentry *upperdentry,
struct ovl_path *lower, unsigned int numlower,
struct ovl_path **stackp, unsigned int *ctrp)
{
struct vfsmount *mnt;
struct dentry *origin = NULL;
int i;
for (i = 0; i < numlower; i++) {
mnt = lower[i].layer->mnt;
origin = ovl_get_origin(upperdentry, mnt);
if (IS_ERR(origin))
return PTR_ERR(origin);
if (origin)
break;
}
if (!origin)
return 0;
BUG_ON(*ctrp);
if (!*stackp)
*stackp = kmalloc(sizeof(struct ovl_path), GFP_KERNEL);
if (!*stackp) {
dput(origin);
return -ENOMEM;
}
**stackp = (struct ovl_path){.dentry = origin, .layer = lower[i].layer};
*ctrp = 1;
return 0;
}
/*
* Verify that @fh matches the origin file handle stored in OVL_XATTR_ORIGIN.
* Return 0 on match, -ESTALE on mismatch, < 0 on error.
*/
static int ovl_verify_origin_fh(struct dentry *dentry, const struct ovl_fh *fh)
{
struct ovl_fh *ofh = ovl_get_origin_fh(dentry);
int err = 0;
if (!ofh)
return -ENODATA;
if (IS_ERR(ofh))
return PTR_ERR(ofh);
if (fh->len != ofh->len || memcmp(fh, ofh, fh->len))
err = -ESTALE;
kfree(ofh);
return err;
}
/*
* Verify that an inode matches the origin file handle stored in upper inode.
*
* If @set is true and there is no stored file handle, encode and store origin
* file handle in OVL_XATTR_ORIGIN.
*
* Return 0 on match, -ESTALE on mismatch, < 0 on error.
*/
int ovl_verify_origin(struct dentry *dentry, struct dentry *origin,
bool is_upper, bool set)
{
struct inode *inode;
struct ovl_fh *fh;
int err;
fh = ovl_encode_fh(origin, is_upper);
err = PTR_ERR(fh);
if (IS_ERR(fh))
goto fail;
err = ovl_verify_origin_fh(dentry, fh);
if (set && err == -ENODATA)
err = ovl_do_setxattr(dentry, OVL_XATTR_ORIGIN, fh, fh->len, 0);
if (err)
goto fail;
out:
kfree(fh);
return err;
fail:
inode = d_inode(origin);
pr_warn_ratelimited("overlayfs: failed to verify origin (%pd2, ino=%lu, err=%i)\n",
origin, inode ? inode->i_ino : 0, err);
goto out;
}
/*
* Verify that an index entry name matches the origin file handle stored in
* OVL_XATTR_ORIGIN and that origin file handle can be decoded to lower path.
* Return 0 on match, -ESTALE on mismatch or stale origin, < 0 on error.
*/
int ovl_verify_index(struct dentry *index, struct ovl_path *lower,
unsigned int numlower)
{
struct ovl_fh *fh = NULL;
size_t len;
struct ovl_path origin = { };
struct ovl_path *stack = &origin;
unsigned int ctr = 0;
int err;
if (!d_inode(index))
return 0;
/*
* Directory index entries are going to be used for looking up
* redirected upper dirs by lower dir fh when decoding an overlay
* file handle of a merge dir. Whiteout index entries are going to be
* used as an indication that an exported overlay file handle should
* be treated as stale (i.e. after unlink of the overlay inode).
* We don't know the verification rules for directory and whiteout
* index entries, because they have not been implemented yet, so return
* EINVAL if those entries are found to abort the mount to avoid
* corrupting an index that was created by a newer kernel.
*/
err = -EINVAL;
if (d_is_dir(index) || ovl_is_whiteout(index))
goto fail;
if (index->d_name.len < sizeof(struct ovl_fh)*2)
goto fail;
err = -ENOMEM;
len = index->d_name.len / 2;
fh = kzalloc(len, GFP_KERNEL);
if (!fh)
goto fail;
err = -EINVAL;
if (hex2bin((u8 *)fh, index->d_name.name, len) || len != fh->len)
goto fail;
err = ovl_verify_origin_fh(index, fh);
if (err)
goto fail;
err = ovl_check_origin(index, lower, numlower, &stack, &ctr);
if (!err && !ctr)
err = -ESTALE;
if (err)
goto fail;
/* Check if index is orphan and don't warn before cleaning it */
if (d_inode(index)->i_nlink == 1 &&
ovl_get_nlink(origin.dentry, index, 0) == 0)
err = -ENOENT;
dput(origin.dentry);
out:
kfree(fh);
return err;
fail:
pr_warn_ratelimited("overlayfs: failed to verify index (%pd2, ftype=%x, err=%i)\n",
index, d_inode(index)->i_mode & S_IFMT, err);
goto out;
}
/*
* Lookup in indexdir for the index entry of a lower real inode or a copy up
* origin inode. The index entry name is the hex representation of the lower
* inode file handle.
*
* If the index dentry in negative, then either no lower aliases have been
* copied up yet, or aliases have been copied up in older kernels and are
* not indexed.
*
* If the index dentry for a copy up origin inode is positive, but points
* to an inode different than the upper inode, then either the upper inode
* has been copied up and not indexed or it was indexed, but since then
* index dir was cleared. Either way, that index cannot be used to indentify
* the overlay inode.
*/
int ovl_get_index_name(struct dentry *origin, struct qstr *name)
{
int err;
struct ovl_fh *fh;
char *n, *s;
fh = ovl_encode_fh(origin, false);
if (IS_ERR(fh))
return PTR_ERR(fh);
err = -ENOMEM;
n = kzalloc(fh->len * 2, GFP_KERNEL);
if (n) {
s = bin2hex(n, fh, fh->len);
*name = (struct qstr) QSTR_INIT(n, s - n);
err = 0;
}
kfree(fh);
return err;
}
static struct dentry *ovl_lookup_index(struct dentry *dentry,
struct dentry *upper,
struct dentry *origin)
{
struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
struct dentry *index;
struct inode *inode;
struct qstr name;
int err;
err = ovl_get_index_name(origin, &name);
if (err)
return ERR_PTR(err);
index = lookup_one_len_unlocked(name.name, ofs->indexdir, name.len);
if (IS_ERR(index)) {
err = PTR_ERR(index);
if (err == -ENOENT) {
index = NULL;
goto out;
}
pr_warn_ratelimited("overlayfs: failed inode index lookup (ino=%lu, key=%*s, err=%i);\n"
"overlayfs: mount with '-o index=off' to disable inodes index.\n",
d_inode(origin)->i_ino, name.len, name.name,
err);
goto out;
}
inode = d_inode(index);
if (d_is_negative(index)) {
goto out_dput;
} else if (upper && d_inode(upper) != inode) {
goto out_dput;
} else if (ovl_dentry_weird(index) || ovl_is_whiteout(index) ||
((inode->i_mode ^ d_inode(origin)->i_mode) & S_IFMT)) {
/*
* Index should always be of the same file type as origin
* except for the case of a whiteout index. A whiteout
* index should only exist if all lower aliases have been
* unlinked, which means that finding a lower origin on lookup
* whose index is a whiteout should be treated as an error.
*/
pr_warn_ratelimited("overlayfs: bad index found (index=%pd2, ftype=%x, origin ftype=%x).\n",
index, d_inode(index)->i_mode & S_IFMT,
d_inode(origin)->i_mode & S_IFMT);
goto fail;
}
out:
kfree(name.name);
return index;
out_dput:
dput(index);
index = NULL;
goto out;
fail:
dput(index);
index = ERR_PTR(-EIO);
goto out;
}
/*
* Returns next layer in stack starting from top.
* Returns -1 if this is the last layer.
*/
int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
{
struct ovl_entry *oe = dentry->d_fsdata;
BUG_ON(idx < 0);
if (idx == 0) {
ovl_path_upper(dentry, path);
if (path->dentry)
return oe->numlower ? 1 : -1;
idx++;
}
BUG_ON(idx > oe->numlower);
path->dentry = oe->lowerstack[idx - 1].dentry;
path->mnt = oe->lowerstack[idx - 1].layer->mnt;
return (idx < oe->numlower) ? idx + 1 : -1;
}
static int ovl_find_layer(struct ovl_fs *ofs, struct ovl_path *path)
{
int i;
for (i = 0; i < ofs->numlower; i++) {
if (ofs->lower_layers[i].mnt == path->layer->mnt)
break;
}
return i;
}
struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
unsigned int flags)
{
struct ovl_entry *oe;
const struct cred *old_cred;
struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
struct ovl_entry *poe = dentry->d_parent->d_fsdata;
struct ovl_entry *roe = dentry->d_sb->s_root->d_fsdata;
struct ovl_path *stack = NULL;
struct dentry *upperdir, *upperdentry = NULL;
struct dentry *index = NULL;
unsigned int ctr = 0;
struct inode *inode = NULL;
bool upperopaque = false;
char *upperredirect = NULL;
struct dentry *this;
unsigned int i;
int err;
struct ovl_lookup_data d = {
.name = dentry->d_name,
.is_dir = false,
.opaque = false,
.stop = false,
.last = !poe->numlower,
.redirect = NULL,
};
if (dentry->d_name.len > ofs->namelen)
return ERR_PTR(-ENAMETOOLONG);
old_cred = ovl_override_creds(dentry->d_sb);
upperdir = ovl_dentry_upper(dentry->d_parent);
if (upperdir) {
err = ovl_lookup_layer(upperdir, &d, &upperdentry);
if (err)
goto out;
if (upperdentry && unlikely(ovl_dentry_remote(upperdentry))) {
dput(upperdentry);
err = -EREMOTE;
goto out;
}
if (upperdentry && !d.is_dir) {
BUG_ON(!d.stop || d.redirect);
/*
* Lookup copy up origin by decoding origin file handle.
* We may get a disconnected dentry, which is fine,
* because we only need to hold the origin inode in
* cache and use its inode number. We may even get a
* connected dentry, that is not under any of the lower
* layers root. That is also fine for using it's inode
* number - it's the same as if we held a reference
* to a dentry in lower layer that was moved under us.
*/
err = ovl_check_origin(upperdentry, roe->lowerstack,
roe->numlower, &stack, &ctr);
if (err)
goto out_put_upper;
}
if (d.redirect) {
err = -ENOMEM;
upperredirect = kstrdup(d.redirect, GFP_KERNEL);
if (!upperredirect)
goto out_put_upper;
if (d.redirect[0] == '/')
poe = roe;
}
upperopaque = d.opaque;
}
if (!d.stop && poe->numlower) {
err = -ENOMEM;
stack = kcalloc(ofs->numlower, sizeof(struct ovl_path),
GFP_KERNEL);
if (!stack)
goto out_put_upper;
}
for (i = 0; !d.stop && i < poe->numlower; i++) {
struct ovl_path lower = poe->lowerstack[i];
d.last = i == poe->numlower - 1;
err = ovl_lookup_layer(lower.dentry, &d, &this);
if (err)
goto out_put;
if (!this)
continue;
stack[ctr].dentry = this;
stack[ctr].layer = lower.layer;
ctr++;
if (d.stop)
break;
/*
* 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 && !ofs->config.redirect_follow) {
pr_warn_ratelimited("overlayfs: refusing to follow redirect for (%pd2)\n",
dentry);
goto out_put;
}
if (d.redirect && d.redirect[0] == '/' && poe != roe) {
poe = roe;
/* Find the current layer on the root dentry */
i = ovl_find_layer(ofs, &lower);
if (WARN_ON(i == ofs->numlower))
break;
}
}
/* Lookup index by lower inode and verify it matches upper inode */
if (ctr && !d.is_dir && ovl_indexdir(dentry->d_sb)) {
struct dentry *origin = stack[0].dentry;
index = ovl_lookup_index(dentry, upperdentry, origin);
if (IS_ERR(index)) {
err = PTR_ERR(index);
index = NULL;
goto out_put;
}
}
oe = ovl_alloc_entry(ctr);
err = -ENOMEM;
if (!oe)
goto out_put;
oe->opaque = upperopaque;
memcpy(oe->lowerstack, stack, sizeof(struct ovl_path) * ctr);
dentry->d_fsdata = oe;
if (upperdentry)
ovl_dentry_set_upper_alias(dentry);
else if (index)
upperdentry = dget(index);
if (upperdentry || ctr) {
inode = ovl_get_inode(dentry, upperdentry, index);
err = PTR_ERR(inode);
if (IS_ERR(inode))
goto out_free_oe;
OVL_I(inode)->redirect = upperredirect;
if (index)
ovl_set_flag(OVL_INDEX, inode);
}
revert_creds(old_cred);
dput(index);
kfree(stack);
kfree(d.redirect);
d_add(dentry, inode);
return NULL;
out_free_oe:
dentry->d_fsdata = NULL;
kfree(oe);
out_put:
dput(index);
for (i = 0; i < ctr; i++)
dput(stack[i].dentry);
kfree(stack);
out_put_upper:
dput(upperdentry);
kfree(upperredirect);
out:
kfree(d.redirect);
revert_creds(old_cred);
return ERR_PTR(err);
}
bool ovl_lower_positive(struct dentry *dentry)
{
struct ovl_entry *oe = dentry->d_fsdata;
struct ovl_entry *poe = dentry->d_parent->d_fsdata;
const struct qstr *name = &dentry->d_name;
const struct cred *old_cred;
unsigned int i;
bool positive = false;
bool done = false;
/*
* If dentry is negative, then lower is positive iff this is a
* whiteout.
*/
if (!dentry->d_inode)
return oe->opaque;
/* Negative upper -> positive lower */
if (!ovl_dentry_upper(dentry))
return true;
old_cred = ovl_override_creds(dentry->d_sb);
/* Positive upper -> have to look up lower to see whether it exists */
for (i = 0; !done && !positive && i < poe->numlower; i++) {
struct dentry *this;
struct dentry *lowerdir = poe->lowerstack[i].dentry;
this = lookup_one_len_unlocked(name->name, lowerdir,
name->len);
if (IS_ERR(this)) {
switch (PTR_ERR(this)) {
case -ENOENT:
case -ENAMETOOLONG:
break;
default:
/*
* Assume something is there, we just couldn't
* access it.
*/
positive = true;
break;
}
} else {
if (this->d_inode) {
positive = !ovl_is_whiteout(this);
done = true;
}
dput(this);
}
}
revert_creds(old_cred);
return positive;
}
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