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quota: fix dqput() to follow the guarantees dquot_srcu should provide

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The dquot_mark_dquot_dirty() using dquot references from the inode
should be protected by dquot_srcu. quota_off code takes care to call
synchronize_srcu(&dquot_srcu) to not drop dquot references while they
are used by other users. But dquot_transfer() breaks this assumption.
We call dquot_transfer() to drop the last reference of dquot and add
it to free_dquots, but there may still be other users using the dquot
at this time, as shown in the function graph below:

       cpu1              cpu2
_________________|_________________
wb_do_writeback         CHOWN(1)
 ...
  ext4_da_update_reserve_space
   dquot_claim_block
    ...
     dquot_mark_dquot_dirty // try to dirty old quota
      test_bit(DQ_ACTIVE_B, &dquot->dq_flags) // still ACTIVE
      if (test_bit(DQ_MOD_B, &dquot->dq_flags))
      // test no dirty, wait dq_list_lock
                    ...
                     dquot_transfer
                      __dquot_transfer
                      dqput_all(transfer_from) // rls old dquot
                       dqput // last dqput
                        dquot_release
                         clear_bit(DQ_ACTIVE_B, &dquot->dq_flags)
                        atomic_dec(&dquot->dq_count)
                        put_dquot_last(dquot)
                         list_add_tail(&dquot->dq_free, &free_dquots)
                         // add the dquot to free_dquots
      if (!test_and_set_bit(DQ_MOD_B, &dquot->dq_flags))
        add dqi_dirty_list // add released dquot to dirty_list

This can cause various issues, such as dquot being destroyed by
dqcache_shrink_scan() after being added to free_dquots, which can trigger
a UAF in dquot_mark_dquot_dirty(); or after dquot is added to free_dquots
and then to dirty_list, it is added to free_dquots again after
dquot_writeback_dquots() is executed, which causes the free_dquots list to
be corrupted and triggers a UAF when dqcache_shrink_scan() is called for
freeing dquot twice.

As Honza said, we need to fix dquot_transfer() to follow the guarantees
dquot_srcu should provide. But calling synchronize_srcu() directly from
dquot_transfer() is too expensive (and mostly unnecessary). So we add
dquot whose last reference should be dropped to the new global dquot
list releasing_dquots, and then queue work item which would call
synchronize_srcu() and after that perform the final cleanup of all the
dquots on releasing_dquots.

Fixes: 4580b30ea8 ("quota: Do not dirty bad dquots")
Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20230630110822.3881712-5-libaokun1@huawei.com>
This commit is contained in:
Baokun Li 2023-06-30 19:08:21 +08:00 committed by Jan Kara
parent 33bcfafc48
commit dabc8b2075
1 changed files with 78 additions and 18 deletions
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96
fs/quota/dquot.c
View File

@ -225,13 +225,22 @@ static void put_quota_format(struct quota_format_type *fmt)
/*
* Dquot List Management:
* The quota code uses four lists for dquot management: the inuse_list,
* free_dquots, dqi_dirty_list, and dquot_hash[] array. A single dquot
* structure may be on some of those lists, depending on its current state.
* The quota code uses five lists for dquot management: the inuse_list,
* releasing_dquots, free_dquots, dqi_dirty_list, and dquot_hash[] array.
* A single dquot structure may be on some of those lists, depending on
* its current state.
*
* All dquots are placed to the end of inuse_list when first created, and this
* list is used for invalidate operation, which must look at every dquot.
*
* When the last reference of a dquot will be dropped, the dquot will be
* added to releasing_dquots. We'd then queue work item which would call
* synchronize_srcu() and after that perform the final cleanup of all the
* dquots on the list. Both releasing_dquots and free_dquots use the
* dq_free list_head in the dquot struct. When a dquot is removed from
* releasing_dquots, a reference count is always subtracted, and if
* dq_count == 0 at that point, the dquot will be added to the free_dquots.
*
* Unused dquots (dq_count == 0) are added to the free_dquots list when freed,
* and this list is searched whenever we need an available dquot. Dquots are
* removed from the list as soon as they are used again, and
@ -250,6 +259,7 @@ static void put_quota_format(struct quota_format_type *fmt)
static LIST_HEAD(inuse_list);
static LIST_HEAD(free_dquots);
static LIST_HEAD(releasing_dquots);
static unsigned int dq_hash_bits, dq_hash_mask;
static struct hlist_head *dquot_hash;
@ -260,6 +270,9 @@ static qsize_t inode_get_rsv_space(struct inode *inode);
static qsize_t __inode_get_rsv_space(struct inode *inode);
static int __dquot_initialize(struct inode *inode, int type);
static void quota_release_workfn(struct work_struct *work);
static DECLARE_DELAYED_WORK(quota_release_work, quota_release_workfn);
static inline unsigned int
hashfn(const struct super_block *sb, struct kqid qid)
{
@ -305,12 +318,18 @@ static inline void put_dquot_last(struct dquot *dquot)
dqstats_inc(DQST_FREE_DQUOTS);
}
static inline void put_releasing_dquots(struct dquot *dquot)
{
list_add_tail(&dquot->dq_free, &releasing_dquots);
}
static inline void remove_free_dquot(struct dquot *dquot)
{
if (list_empty(&dquot->dq_free))
return;
list_del_init(&dquot->dq_free);
dqstats_dec(DQST_FREE_DQUOTS);
if (!atomic_read(&dquot->dq_count))
dqstats_dec(DQST_FREE_DQUOTS);
}
static inline void put_inuse(struct dquot *dquot)
@ -552,6 +571,8 @@ static void invalidate_dquots(struct super_block *sb, int type)
struct dquot *dquot, *tmp;
restart:
flush_delayed_work(&quota_release_work);
spin_lock(&dq_list_lock);
list_for_each_entry_safe(dquot, tmp, &inuse_list, dq_inuse) {
if (dquot->dq_sb != sb)
@ -560,6 +581,12 @@ static void invalidate_dquots(struct super_block *sb, int type)
continue;
/* Wait for dquot users */
if (atomic_read(&dquot->dq_count)) {
/* dquot in releasing_dquots, flush and retry */
if (!list_empty(&dquot->dq_free)) {
spin_unlock(&dq_list_lock);
goto restart;
}
atomic_inc(&dquot->dq_count);
spin_unlock(&dq_list_lock);
/*
@ -770,6 +797,49 @@ static struct shrinker dqcache_shrinker = {
.seeks = DEFAULT_SEEKS,
};
/*
* Safely release dquot and put reference to dquot.
*/
static void quota_release_workfn(struct work_struct *work)
{
struct dquot *dquot;
struct list_head rls_head;
spin_lock(&dq_list_lock);
/* Exchange the list head to avoid livelock. */
list_replace_init(&releasing_dquots, &rls_head);
spin_unlock(&dq_list_lock);
restart:
synchronize_srcu(&dquot_srcu);
spin_lock(&dq_list_lock);
while (!list_empty(&rls_head)) {
dquot = list_first_entry(&rls_head, struct dquot, dq_free);
/* Dquot got used again? */
if (atomic_read(&dquot->dq_count) > 1) {
remove_free_dquot(dquot);
atomic_dec(&dquot->dq_count);
continue;
}
if (dquot_dirty(dquot)) {
spin_unlock(&dq_list_lock);
/* Commit dquot before releasing */
dquot_write_dquot(dquot);
goto restart;
}
if (dquot_active(dquot)) {
spin_unlock(&dq_list_lock);
dquot->dq_sb->dq_op->release_dquot(dquot);
goto restart;
}
/* Dquot is inactive and clean, now move it to free list */
remove_free_dquot(dquot);
atomic_dec(&dquot->dq_count);
put_dquot_last(dquot);
}
spin_unlock(&dq_list_lock);
}
/*
* Put reference to dquot
*/
@ -786,7 +856,7 @@ void dqput(struct dquot *dquot)
}
#endif
dqstats_inc(DQST_DROPS);
we_slept:
spin_lock(&dq_list_lock);
if (atomic_read(&dquot->dq_count) > 1) {
/* We have more than one user... nothing to do */
@ -798,25 +868,15 @@ void dqput(struct dquot *dquot)
spin_unlock(&dq_list_lock);
return;
}
/* Need to release dquot? */
if (dquot_dirty(dquot)) {
spin_unlock(&dq_list_lock);
/* Commit dquot before releasing */
dquot_write_dquot(dquot);
goto we_slept;
}
if (dquot_active(dquot)) {
spin_unlock(&dq_list_lock);
dquot->dq_sb->dq_op->release_dquot(dquot);
goto we_slept;
}
atomic_dec(&dquot->dq_count);
#ifdef CONFIG_QUOTA_DEBUG
/* sanity check */
BUG_ON(!list_empty(&dquot->dq_free));
#endif
put_dquot_last(dquot);
put_releasing_dquots(dquot);
spin_unlock(&dq_list_lock);
queue_delayed_work(system_unbound_wq, &quota_release_work, 1);
}
EXPORT_SYMBOL(dqput);