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authorBaokun Li <libaokun1@huawei.com>2023-06-30 13:08:21 +0200
committerJan Kara <jack@suse.cz>2023-07-03 19:00:19 +0200
commitdabc8b20756601b9e1cc85a81d47d3f98ed4d13a (patch)
tree82710d2ea68b8b2060f85cc984887783cbc4324d /fs/quota/dquot.c
parentquota: add new helper dquot_active() (diff)
downloadlinux-dabc8b20756601b9e1cc85a81d47d3f98ed4d13a.tar.xz
linux-dabc8b20756601b9e1cc85a81d47d3f98ed4d13a.zip
quota: fix dqput() to follow the guarantees dquot_srcu should provide
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: 4580b30ea887 ("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>
Diffstat (limited to '')
-rw-r--r--fs/quota/dquot.c96
1 files changed, 78 insertions, 18 deletions
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 88aa747f4800..c7afe433d991 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -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 @@ restart:
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);
/*
@@ -771,6 +798,49 @@ static struct shrinker dqcache_shrinker = {
};
/*
+ * 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
*/
void dqput(struct dquot *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 @@ we_slept:
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);