[PATCH] jbd2: user-memory-access in jbd2__journal_start

[Edward Adam Davis <eadavis@xxxxxx>]

Before reusing the handle, it is necessary to confirm that the transaction is 
ready.

Reported-and-tested-by: syzbot+cdee56dbcdf0096ef605@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
---
 fs/jbd2/transaction.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index cb0b8d6fc0c6..702312cd5392 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -493,6 +493,9 @@ handle_t *jbd2__journal_start(journal_t *journal, int nblocks, int rsv_blocks,
 		return ERR_PTR(-EROFS);
 
 	if (handle) {
+		if (handle->saved_alloc_context & ~PF_MEMALLOC_NOFS)
+			return ERR_PTR(-EBUSY);
+
 		J_ASSERT(handle->h_transaction->t_journal == journal);
 		handle->h_ref++;
 		return handle;
-- 
2.43.0