[PATCH] ocfs2: revalidate the journal dinode before toggling dirty

[ZhengYuan Huang]

[BUG]
A fuzzed OCFS2 image can corrupt the current slot journal dinode while
mount is still in progress. The mount path first reports the invalid
journal block and then crashes in shutdown:

kernel BUG at fs/ocfs2/journal.c:1034!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
RIP: 0010:ocfs2_journal_toggle_dirty+0x2d6/0x340 fs/ocfs2/journal.c:1034
Call Trace:
 ocfs2_journal_shutdown+0x414/0xc30 fs/ocfs2/journal.c:1116
 ocfs2_mount_volume fs/ocfs2/super.c:1785 [inline]
 ocfs2_fill_super+0x30a9/0x3cd0 fs/ocfs2/super.c:1083
 get_tree_bdev_flags+0x38b/0x640 fs/super.c:1698
 get_tree_bdev+0x24/0x40 fs/super.c:1721
 ocfs2_get_tree+0x21/0x30 fs/ocfs2/super.c:1184
 vfs_get_tree+0x9a/0x370 fs/super.c:1758
 fc_mount fs/namespace.c:1199 [inline]
 do_new_mount_fc fs/namespace.c:3642 [inline]
 do_new_mount fs/namespace.c:3718 [inline]
 path_mount+0x5b8/0x1ea0 fs/namespace.c:4028
 do_mount fs/namespace.c:4041 [inline]
 __do_sys_mount fs/namespace.c:4229 [inline]
 __se_sys_mount fs/namespace.c:4206 [inline]
 __x64_sys_mount+0x282/0x320 fs/namespace.c:4206
 ...


[CAUSE]
ocfs2_journal_toggle_dirty() assumes journal->j_bh still contains the
same validated dinode that ocfs2_journal_init() locked earlier, and it
uses BUG_ON() when the buffer no longer looks like a dinode. That
assumption is too strong. The mount path can force the same current-slot
journal inode block back in from disk through
ocfs2_read_journal_inode(..., OCFS2_BH_IGNORE_CACHE) while
ocfs2_mark_dead_nodes() scans the journal slots. If that reread finds
corrupted metadata, mount unwinds through ocfs2_journal_shutdown(),
which reuses journal->j_bh and turns the metadata corruption into a
kernel BUG.

[FIX]
Revalidate journal->j_bh with ocfs2_validate_inode_block() before
updating the dirty flag. If the cached journal dinode has become
invalid, return the corruption error and keep the failure on OCFS2's
normal read-only/error path instead of crashing the kernel. This
revalidation happens in the cold path of mount, so the performance
impact should be negligible.

Signed-off-by: ZhengYuan Huang <gality369@xxxxxxxxx>
---
 fs/ocfs2/journal.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c
index f9bf3bac085d..c9a972a1304e 100644
--- a/fs/ocfs2/journal.c
+++ b/fs/ocfs2/journal.c
@@ -1021,12 +1021,15 @@ static int ocfs2_journal_toggle_dirty(struct ocfs2_super *osb,
 	struct buffer_head *bh = journal->j_bh;
 	struct ocfs2_dinode *fe;
 
-	fe = (struct ocfs2_dinode *)bh->b_data;
+	/* The journal inode block can be forced back in from disk while the
+	 * mount path is still running, so validate the cached bh again before
+	 * updating the journal state on disk.
+	 */
+	status = ocfs2_validate_inode_block(osb->sb, bh);
+	if (status < 0)
+		return status;
 
-	/* The journal bh on the osb always comes from ocfs2_journal_init()
-	 * and was validated there inside ocfs2_inode_lock_full().  It's a
-	 * code bug if we mess it up. */
-	BUG_ON(!OCFS2_IS_VALID_DINODE(fe));
+	fe = (struct ocfs2_dinode *)bh->b_data;
 
 	flags = le32_to_cpu(fe->id1.journal1.ij_flags);
 	if (dirty)
-- 
2.49.0