path: root/fs
diff options
authorLukas Czerner <>2015-05-14 18:55:18 -0400
committerTheodore Ts'o <>2015-05-14 18:55:18 -0400
commit9d506594069355d1fb2de3f9104667312ff08ed3 (patch)
treee3e6bcf3c89f03a0b2bc68664fd04a6d39cbd0c6 /fs
parent92c82639106214a9d34daa2bc791605eb1faab07 (diff)
ext4: fix NULL pointer dereference when journal restart fails
Currently when journal restart fails, we'll have the h_transaction of the handle set to NULL to indicate that the handle has been effectively aborted. We handle this situation quietly in the jbd2_journal_stop() and just free the handle and exit because everything else has been done before we attempted (and failed) to restart the journal. Unfortunately there are a number of problems with that approach introduced with commit 41a5b913197c "jbd2: invalidate handle if jbd2_journal_restart() fails" First of all in ext4 jbd2_journal_stop() will be called through __ext4_journal_stop() where we would try to get a hold of the superblock by dereferencing h_transaction which in this case would lead to NULL pointer dereference and crash. In addition we're going to free the handle regardless of the refcount which is bad as well, because others up the call chain will still reference the handle so we might potentially reference already freed memory. Moreover it's expected that we'll get aborted handle as well as detached handle in some of the journalling function as the error propagates up the stack, so it's unnecessary to call WARN_ON every time we get detached handle. And finally we might leak some memory by forgetting to free reserved handle in jbd2_journal_stop() in the case where handle was detached from the transaction (h_transaction is NULL). Fix the NULL pointer dereference in __ext4_journal_stop() by just calling jbd2_journal_stop() quietly as suggested by Jan Kara. Also fix the potential memory leak in jbd2_journal_stop() and use proper handle refcounting before we attempt to free it to avoid use-after-free issues. And finally remove all WARN_ON(!transaction) from the code so that we do not get random traces when something goes wrong because when journal restart fails we will get to some of those functions. Cc: Signed-off-by: Lukas Czerner <> Signed-off-by: Theodore Ts'o <> Reviewed-by: Jan Kara <>
Diffstat (limited to 'fs')
2 files changed, 22 insertions, 9 deletions
diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
index 3445035c7e01..d41843181818 100644
--- a/fs/ext4/ext4_jbd2.c
+++ b/fs/ext4/ext4_jbd2.c
@@ -87,6 +87,12 @@ int __ext4_journal_stop(const char *where, unsigned int line, handle_t *handle)
return 0;
+ if (!handle->h_transaction) {
+ err = jbd2_journal_stop(handle);
+ return handle->h_err ? handle->h_err : err;
+ }
sb = handle->h_transaction->t_journal->j_private;
err = handle->h_err;
rc = jbd2_journal_stop(handle);
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 5f09370c90a8..ff2f2e6ad311 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -551,7 +551,6 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
int result;
int wanted;
- WARN_ON(!transaction);
if (is_handle_aborted(handle))
return -EROFS;
journal = transaction->t_journal;
@@ -627,7 +626,6 @@ int jbd2__journal_restart(handle_t *handle, int nblocks, gfp_t gfp_mask)
tid_t tid;
int need_to_start, ret;
- WARN_ON(!transaction);
/* If we've had an abort of any type, don't even think about
* actually doing the restart! */
if (is_handle_aborted(handle))
@@ -785,7 +783,6 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
int need_copy = 0;
unsigned long start_lock, time_lock;
- WARN_ON(!transaction);
if (is_handle_aborted(handle))
return -EROFS;
journal = transaction->t_journal;
@@ -1051,7 +1048,6 @@ int jbd2_journal_get_create_access(handle_t *handle, struct buffer_head *bh)
int err;
jbd_debug(5, "journal_head %p\n", jh);
- WARN_ON(!transaction);
err = -EROFS;
if (is_handle_aborted(handle))
goto out;
@@ -1266,7 +1262,6 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
struct journal_head *jh;
int ret = 0;
- WARN_ON(!transaction);
if (is_handle_aborted(handle))
return -EROFS;
journal = transaction->t_journal;
@@ -1397,7 +1392,6 @@ int jbd2_journal_forget (handle_t *handle, struct buffer_head *bh)
int err = 0;
int was_modified = 0;
- WARN_ON(!transaction);
if (is_handle_aborted(handle))
return -EROFS;
journal = transaction->t_journal;
@@ -1530,8 +1524,22 @@ int jbd2_journal_stop(handle_t *handle)
tid_t tid;
pid_t pid;
- if (!transaction)
- goto free_and_exit;
+ if (!transaction) {
+ /*
+ * Handle is already detached from the transaction so
+ * there is nothing to do other than decrease a refcount,
+ * or free the handle if refcount drops to zero
+ */
+ if (--handle->h_ref > 0) {
+ jbd_debug(4, "h_ref %d -> %d\n", handle->h_ref + 1,
+ handle->h_ref);
+ return err;
+ } else {
+ if (handle->h_rsv_handle)
+ jbd2_free_handle(handle->h_rsv_handle);
+ goto free_and_exit;
+ }
+ }
journal = transaction->t_journal;
J_ASSERT(journal_current_handle() == handle);
@@ -2373,7 +2381,6 @@ int jbd2_journal_file_inode(handle_t *handle, struct jbd2_inode *jinode)
transaction_t *transaction = handle->h_transaction;
journal_t *journal;
- WARN_ON(!transaction);
if (is_handle_aborted(handle))
return -EROFS;
journal = transaction->t_journal;