linux/mm/shmem_quota.c
Carlos Maiolino 0a69b6b3a0 tmpfs: fix race on handling dquot rbtree
A syzkaller reproducer found a race while attempting to remove dquot
information from the rb tree.

Fetching the rb_tree root node must also be protected by the
dqopt->dqio_sem, otherwise, giving the right timing, shmem_release_dquot()
will trigger a warning because it couldn't find a node in the tree, when
the real reason was the root node changing before the search starts:

Thread 1				Thread 2
- shmem_release_dquot()			- shmem_{acquire,release}_dquot()

- fetch ROOT				- Fetch ROOT

					- acquire dqio_sem
- wait dqio_sem

					- do something, triger a tree rebalance
					- release dqio_sem

- acquire dqio_sem
- start searching for the node, but
  from the wrong location, missing
  the node, and triggering a warning.

Link: https://lkml.kernel.org/r/20240320124011.398847-1-cem@kernel.org
Fixes: eafc474e20 ("shmem: prepare shmem quota infrastructure")
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Reported-by: Ubisectech Sirius <bugreport@ubisectech.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-03-26 11:07:23 -07:00

355 lines
9.5 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* In memory quota format relies on quota infrastructure to store dquot
* information for us. While conventional quota formats for file systems
* with persistent storage can load quota information into dquot from the
* storage on-demand and hence quota dquot shrinker can free any dquot
* that is not currently being used, it must be avoided here. Otherwise we
* can lose valuable information, user provided limits, because there is
* no persistent storage to load the information from afterwards.
*
* One information that in-memory quota format needs to keep track of is
* a sorted list of ids for each quota type. This is done by utilizing
* an rb tree which root is stored in mem_dqinfo->dqi_priv for each quota
* type.
*
* This format can be used to support quota on file system without persistent
* storage such as tmpfs.
*
* Author: Lukas Czerner <lczerner@redhat.com>
* Carlos Maiolino <cmaiolino@redhat.com>
*
* Copyright (C) 2023 Red Hat, Inc.
*/
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/rbtree.h>
#include <linux/shmem_fs.h>
#include <linux/quotaops.h>
#include <linux/quota.h>
#ifdef CONFIG_TMPFS_QUOTA
/*
* The following constants define the amount of time given a user
* before the soft limits are treated as hard limits (usually resulting
* in an allocation failure). The timer is started when the user crosses
* their soft limit, it is reset when they go below their soft limit.
*/
#define SHMEM_MAX_IQ_TIME 604800 /* (7*24*60*60) 1 week */
#define SHMEM_MAX_DQ_TIME 604800 /* (7*24*60*60) 1 week */
struct quota_id {
struct rb_node node;
qid_t id;
qsize_t bhardlimit;
qsize_t bsoftlimit;
qsize_t ihardlimit;
qsize_t isoftlimit;
};
static int shmem_check_quota_file(struct super_block *sb, int type)
{
/* There is no real quota file, nothing to do */
return 1;
}
/*
* There is no real quota file. Just allocate rb_root for quota ids and
* set limits
*/
static int shmem_read_file_info(struct super_block *sb, int type)
{
struct quota_info *dqopt = sb_dqopt(sb);
struct mem_dqinfo *info = &dqopt->info[type];
info->dqi_priv = kzalloc(sizeof(struct rb_root), GFP_NOFS);
if (!info->dqi_priv)
return -ENOMEM;
info->dqi_max_spc_limit = SHMEM_QUOTA_MAX_SPC_LIMIT;
info->dqi_max_ino_limit = SHMEM_QUOTA_MAX_INO_LIMIT;
info->dqi_bgrace = SHMEM_MAX_DQ_TIME;
info->dqi_igrace = SHMEM_MAX_IQ_TIME;
info->dqi_flags = 0;
return 0;
}
static int shmem_write_file_info(struct super_block *sb, int type)
{
/* There is no real quota file, nothing to do */
return 0;
}
/*
* Free all the quota_id entries in the rb tree and rb_root.
*/
static int shmem_free_file_info(struct super_block *sb, int type)
{
struct mem_dqinfo *info = &sb_dqopt(sb)->info[type];
struct rb_root *root = info->dqi_priv;
struct quota_id *entry;
struct rb_node *node;
info->dqi_priv = NULL;
node = rb_first(root);
while (node) {
entry = rb_entry(node, struct quota_id, node);
node = rb_next(&entry->node);
rb_erase(&entry->node, root);
kfree(entry);
}
kfree(root);
return 0;
}
static int shmem_get_next_id(struct super_block *sb, struct kqid *qid)
{
struct mem_dqinfo *info = sb_dqinfo(sb, qid->type);
struct rb_node *node;
qid_t id = from_kqid(&init_user_ns, *qid);
struct quota_info *dqopt = sb_dqopt(sb);
struct quota_id *entry = NULL;
int ret = 0;
if (!sb_has_quota_active(sb, qid->type))
return -ESRCH;
down_read(&dqopt->dqio_sem);
node = ((struct rb_root *)info->dqi_priv)->rb_node;
while (node) {
entry = rb_entry(node, struct quota_id, node);
if (id < entry->id)
node = node->rb_left;
else if (id > entry->id)
node = node->rb_right;
else
goto got_next_id;
}
if (!entry) {
ret = -ENOENT;
goto out_unlock;
}
if (id > entry->id) {
node = rb_next(&entry->node);
if (!node) {
ret = -ENOENT;
goto out_unlock;
}
entry = rb_entry(node, struct quota_id, node);
}
got_next_id:
*qid = make_kqid(&init_user_ns, qid->type, entry->id);
out_unlock:
up_read(&dqopt->dqio_sem);
return ret;
}
/*
* Load dquot with limits from existing entry, or create the new entry if
* it does not exist.
*/
static int shmem_acquire_dquot(struct dquot *dquot)
{
struct mem_dqinfo *info = sb_dqinfo(dquot->dq_sb, dquot->dq_id.type);
struct rb_node **n;
struct shmem_sb_info *sbinfo = dquot->dq_sb->s_fs_info;
struct rb_node *parent = NULL, *new_node = NULL;
struct quota_id *new_entry, *entry;
qid_t id = from_kqid(&init_user_ns, dquot->dq_id);
struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
int ret = 0;
mutex_lock(&dquot->dq_lock);
down_write(&dqopt->dqio_sem);
n = &((struct rb_root *)info->dqi_priv)->rb_node;
while (*n) {
parent = *n;
entry = rb_entry(parent, struct quota_id, node);
if (id < entry->id)
n = &(*n)->rb_left;
else if (id > entry->id)
n = &(*n)->rb_right;
else
goto found;
}
/* We don't have entry for this id yet, create it */
new_entry = kzalloc(sizeof(struct quota_id), GFP_NOFS);
if (!new_entry) {
ret = -ENOMEM;
goto out_unlock;
}
new_entry->id = id;
if (dquot->dq_id.type == USRQUOTA) {
new_entry->bhardlimit = sbinfo->qlimits.usrquota_bhardlimit;
new_entry->ihardlimit = sbinfo->qlimits.usrquota_ihardlimit;
} else if (dquot->dq_id.type == GRPQUOTA) {
new_entry->bhardlimit = sbinfo->qlimits.grpquota_bhardlimit;
new_entry->ihardlimit = sbinfo->qlimits.grpquota_ihardlimit;
}
new_node = &new_entry->node;
rb_link_node(new_node, parent, n);
rb_insert_color(new_node, (struct rb_root *)info->dqi_priv);
entry = new_entry;
found:
/* Load the stored limits from the tree */
spin_lock(&dquot->dq_dqb_lock);
dquot->dq_dqb.dqb_bhardlimit = entry->bhardlimit;
dquot->dq_dqb.dqb_bsoftlimit = entry->bsoftlimit;
dquot->dq_dqb.dqb_ihardlimit = entry->ihardlimit;
dquot->dq_dqb.dqb_isoftlimit = entry->isoftlimit;
if (!dquot->dq_dqb.dqb_bhardlimit &&
!dquot->dq_dqb.dqb_bsoftlimit &&
!dquot->dq_dqb.dqb_ihardlimit &&
!dquot->dq_dqb.dqb_isoftlimit)
set_bit(DQ_FAKE_B, &dquot->dq_flags);
spin_unlock(&dquot->dq_dqb_lock);
/* Make sure flags update is visible after dquot has been filled */
smp_mb__before_atomic();
set_bit(DQ_ACTIVE_B, &dquot->dq_flags);
out_unlock:
up_write(&dqopt->dqio_sem);
mutex_unlock(&dquot->dq_lock);
return ret;
}
static bool shmem_is_empty_dquot(struct dquot *dquot)
{
struct shmem_sb_info *sbinfo = dquot->dq_sb->s_fs_info;
qsize_t bhardlimit;
qsize_t ihardlimit;
if (dquot->dq_id.type == USRQUOTA) {
bhardlimit = sbinfo->qlimits.usrquota_bhardlimit;
ihardlimit = sbinfo->qlimits.usrquota_ihardlimit;
} else if (dquot->dq_id.type == GRPQUOTA) {
bhardlimit = sbinfo->qlimits.grpquota_bhardlimit;
ihardlimit = sbinfo->qlimits.grpquota_ihardlimit;
}
if (test_bit(DQ_FAKE_B, &dquot->dq_flags) ||
(dquot->dq_dqb.dqb_curspace == 0 &&
dquot->dq_dqb.dqb_curinodes == 0 &&
dquot->dq_dqb.dqb_bhardlimit == bhardlimit &&
dquot->dq_dqb.dqb_ihardlimit == ihardlimit))
return true;
return false;
}
/*
* Store limits from dquot in the tree unless it's fake. If it is fake
* remove the id from the tree since there is no useful information in
* there.
*/
static int shmem_release_dquot(struct dquot *dquot)
{
struct mem_dqinfo *info = sb_dqinfo(dquot->dq_sb, dquot->dq_id.type);
struct rb_node *node;
qid_t id = from_kqid(&init_user_ns, dquot->dq_id);
struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
struct quota_id *entry = NULL;
mutex_lock(&dquot->dq_lock);
/* Check whether we are not racing with some other dqget() */
if (dquot_is_busy(dquot))
goto out_dqlock;
down_write(&dqopt->dqio_sem);
node = ((struct rb_root *)info->dqi_priv)->rb_node;
while (node) {
entry = rb_entry(node, struct quota_id, node);
if (id < entry->id)
node = node->rb_left;
else if (id > entry->id)
node = node->rb_right;
else
goto found;
}
/* We should always find the entry in the rb tree */
WARN_ONCE(1, "quota id %u from dquot %p, not in rb tree!\n", id, dquot);
up_write(&dqopt->dqio_sem);
mutex_unlock(&dquot->dq_lock);
return -ENOENT;
found:
if (shmem_is_empty_dquot(dquot)) {
/* Remove entry from the tree */
rb_erase(&entry->node, info->dqi_priv);
kfree(entry);
} else {
/* Store the limits in the tree */
spin_lock(&dquot->dq_dqb_lock);
entry->bhardlimit = dquot->dq_dqb.dqb_bhardlimit;
entry->bsoftlimit = dquot->dq_dqb.dqb_bsoftlimit;
entry->ihardlimit = dquot->dq_dqb.dqb_ihardlimit;
entry->isoftlimit = dquot->dq_dqb.dqb_isoftlimit;
spin_unlock(&dquot->dq_dqb_lock);
}
clear_bit(DQ_ACTIVE_B, &dquot->dq_flags);
up_write(&dqopt->dqio_sem);
out_dqlock:
mutex_unlock(&dquot->dq_lock);
return 0;
}
static int shmem_mark_dquot_dirty(struct dquot *dquot)
{
return 0;
}
static int shmem_dquot_write_info(struct super_block *sb, int type)
{
return 0;
}
static const struct quota_format_ops shmem_format_ops = {
.check_quota_file = shmem_check_quota_file,
.read_file_info = shmem_read_file_info,
.write_file_info = shmem_write_file_info,
.free_file_info = shmem_free_file_info,
};
struct quota_format_type shmem_quota_format = {
.qf_fmt_id = QFMT_SHMEM,
.qf_ops = &shmem_format_ops,
.qf_owner = THIS_MODULE
};
const struct dquot_operations shmem_quota_operations = {
.acquire_dquot = shmem_acquire_dquot,
.release_dquot = shmem_release_dquot,
.alloc_dquot = dquot_alloc,
.destroy_dquot = dquot_destroy,
.write_info = shmem_dquot_write_info,
.mark_dirty = shmem_mark_dquot_dirty,
.get_next_id = shmem_get_next_id,
};
#endif /* CONFIG_TMPFS_QUOTA */