diff mbox series

[Concept,17/26] ext4l: Prevent freeing buffer_heads with active journal_heads

Message ID 20251231223008.3251711-18-sjg@u-boot.org
State New
Headers
Series ext4l: Add write support (part L) |

Commit Message

Simon Glass Dec. 31, 2025, 10:29 p.m. UTC 
  From: Simon Glass <simon.glass@canonical.com>

When running filesystem tests back-to-back, buffer_heads could be freed
while journal_heads still reference them. This causes use-after-free
crashes when the journal code later accesses the stale b_bh pointer.

Add protection in free_buffer_head() to skip buffers with JBD attached,
since the journal owns a reference and will clean them up properly. Also
add protection in brelse() to prevent the ref count from dropping to
zero while JBD is still attached.

Update comments in ext4l_close_internal() to clarify why cache cleanup
is critical even during skip_io mode.

Fixes crashes when test_fs13 runs after test_fs11 in the same session.

Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>
---

 fs/ext4l/support.c | 9 +++++++++
 1 file changed, 9 insertions(+)
diff mbox series

Patch

diff --git a/fs/ext4l/support.c b/fs/ext4l/support.c
index aaaf89092eb..3be40b6fca2 100644
--- a/fs/ext4l/support.c
+++ b/fs/ext4l/support.c
@@ -466,6 +466,15 @@  void free_buffer_head(struct buffer_head *bh)
 	if (!bh)
 		return;
 
+	/*
+	 * Never free a buffer_head that has a journal_head attached.
+	 * This would cause use-after-free when the journal tries to access it.
+	 * The journal owns a reference and the buffer will be cleaned up when
+	 * the journal_head is properly released.
+	 */
+	if (buffer_jbd(bh))
+		return;
+
 	/*
 	 * Shadow buffers (b_private != NULL) share their folio with the
 	 * original buffer. Don't free the shared folio.