There is a race between bdev_try_to_free_page() and
jbd2_journal_destroy() that could end up triggering a use after free
issue about journal.
drop cache umount filesystem
bdev_try_to_free_page()
get journal
jbd2_journal_try_to_free_buffers() ext4_put_super()
kfree(journal)
access journal <-- lead to UAF
The above race also could happens between the bdev_try_to_free_page()
and the error path of ext4_fill_super(). This patch avoid this race by
add rcu protection around accessing sbi->s_journal in
bdev_try_to_free_page() and destroy the journal after an rcu grace
period.
Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
fs/ext4/super.c | 33 ++++++++++++++++++++++++---------
fs/jbd2/journal.c | 30 +++++++++++++++++++++++++++---
include/linux/jbd2.h | 11 ++++++++++-
3 files changed, 61 insertions(+), 13 deletions(-)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 02ba47a5bc70..6bbaadc5357b 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1150,6 +1150,21 @@ static inline void ext4_quota_off_umount(struct super_block *sb)
}
#endif
+static int ext4_journal_release(struct ext4_sb_info *sbi)
+{
+ journal_t *journal = sbi->s_journal;
+ int ret;
+
+ ret = jbd2_journal_release(journal);
+ sbi->s_journal = NULL;
+ /*
+ * Call rcu to prevent racing with bdev_try_to_free_page()
+ * accessing the journal at the same time.
+ */
+ call_rcu(&journal->j_rcu, jbd2_journal_release_rcu);
+ return ret;
+}
+
static void ext4_put_super(struct super_block *sb)
{
struct ext4_sb_info *sbi = EXT4_SB(sb);
@@ -1174,11 +1189,9 @@ static void ext4_put_super(struct super_block *sb)
if (sbi->s_journal) {
aborted = is_journal_aborted(sbi->s_journal);
- err = jbd2_journal_destroy(sbi->s_journal);
- sbi->s_journal = NULL;
- if ((err < 0) && !aborted) {
+ err = ext4_journal_release(sbi);
+ if ((err < 0) && !aborted)
ext4_abort(sb, -err, "Couldn't clean up the journal");
- }
}
ext4_es_unregister_shrinker(sbi);
@@ -1449,14 +1462,18 @@ static int ext4_nfs_commit_metadata(struct inode *inode)
static int bdev_try_to_free_page(struct super_block *sb, struct page *page,
gfp_t wait)
{
- journal_t *journal = EXT4_SB(sb)->s_journal;
+ journal_t *journal;
int ret = 0;
WARN_ON(PageChecked(page));
if (!page_has_buffers(page))
return 0;
+
+ rcu_read_lock();
+ journal = READ_ONCE(EXT4_SB(sb)->s_journal);
if (journal)
ret = jbd2_journal_try_to_free_buffers(journal, page);
+ rcu_read_unlock();
if (!ret)
return try_to_free_buffers(page);
return 0;
@@ -5146,10 +5163,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
ext4_xattr_destroy_cache(sbi->s_ea_block_cache);
sbi->s_ea_block_cache = NULL;
- if (sbi->s_journal) {
- jbd2_journal_destroy(sbi->s_journal);
- sbi->s_journal = NULL;
- }
+ if (sbi->s_journal)
+ ext4_journal_release(sbi);
failed_mount3a:
ext4_es_unregister_shrinker(sbi);
failed_mount3:
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 2dc944442802..071caaaa9de1 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -76,6 +76,8 @@ EXPORT_SYMBOL(jbd2_journal_check_available_features);
EXPORT_SYMBOL(jbd2_journal_set_features);
EXPORT_SYMBOL(jbd2_journal_load);
EXPORT_SYMBOL(jbd2_journal_destroy);
+EXPORT_SYMBOL(jbd2_journal_release);
+EXPORT_SYMBOL(jbd2_journal_release_rcu);
EXPORT_SYMBOL(jbd2_journal_abort);
EXPORT_SYMBOL(jbd2_journal_errno);
EXPORT_SYMBOL(jbd2_journal_ack_err);
@@ -1951,14 +1953,14 @@ int jbd2_journal_load(journal_t *journal)
}
/**
- * jbd2_journal_destroy() - Release a journal_t structure.
+ * jbd2_journal_release() - Release a journal_t structure.
* @journal: Journal to act on.
*
* Release a journal_t structure once it is no longer in use by the
* journaled object.
* Return <0 if we couldn't clean up the journal.
*/
-int jbd2_journal_destroy(journal_t *journal)
+int jbd2_journal_release(journal_t *journal)
{
int err = 0;
@@ -2021,11 +2023,33 @@ int jbd2_journal_destroy(journal_t *journal)
crypto_free_shash(journal->j_chksum_driver);
kfree(journal->j_fc_wbuf);
kfree(journal->j_wbuf);
- kfree(journal);
return err;
}
+/**
+ * jbd2_journal_release_rcu() - Free a journal_t structure.
+ * @rcu: rcu list node relate to the journal want to free.
+ *
+ * Freeing a journal_t structure after a rcu grace period.
+ */
+void jbd2_journal_release_rcu(struct rcu_head *rcu)
+{
+ kfree(container_of(rcu, journal_t, j_rcu));
+}
+
+/**
+ * jbd2_journal_destroy() - Release and free a journal_t structure.
+ * @journal: Journal to act on.
+ *
+ * Release and free a journal_t structure once it is no longer in use
+ * by the journaled object.
+ */
+void jbd2_journal_destroy(journal_t *journal)
+{
+ jbd2_journal_release(journal);
+ kfree(journal);
+}
/**
* jbd2_journal_check_used_features() - Check if features specified are used.
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 99d3cd051ac3..39a8d04596a2 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -1238,6 +1238,13 @@ struct journal_s
*/
__u32 j_csum_seed;
+ /**
+ * @j_rcu:
+ *
+ * Prevent racing between accessing and destroy at the same time.
+ */
+ struct rcu_head j_rcu;
+
#ifdef CONFIG_DEBUG_LOCK_ALLOC
/**
* @j_trans_commit_map:
@@ -1509,7 +1516,9 @@ extern int jbd2_journal_set_features
extern void jbd2_journal_clear_features
(journal_t *, unsigned long, unsigned long, unsigned long);
extern int jbd2_journal_load (journal_t *journal);
-extern int jbd2_journal_destroy (journal_t *);
+extern void jbd2_journal_destroy (journal_t *);
+extern int jbd2_journal_release (journal_t *);
+extern void jbd2_journal_release_rcu (struct rcu_head *rcu);
extern int jbd2_journal_recover (journal_t *journal);
extern int jbd2_journal_wipe (journal_t *, int);
extern int jbd2_journal_skip_recovery (journal_t *);
--
2.25.4
