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author | Baokun Li <libaokun1@huawei.com> | 2023-06-30 13:08:21 +0200 |
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committer | Jan Kara <jack@suse.cz> | 2023-07-03 19:00:19 +0200 |
commit | dabc8b20756601b9e1cc85a81d47d3f98ed4d13a (patch) | |
tree | 82710d2ea68b8b2060f85cc984887783cbc4324d /fs/quota/dquot.c | |
parent | quota: add new helper dquot_active() (diff) | |
download | linux-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.c | 96 |
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("a_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, "a_release_work, 1); } EXPORT_SYMBOL(dqput); |