[PATCH 2/2] osfs2: Fix kernel BUG in ocfs2_write_cluster

[Mohammed Anees <pvmohammedanees2003@gmail.com>]

syzbot has found a kernel BUG in ocfs2_write_cluster_by_desc [1].

The issue arises because ocfs2_insert_extent receives start_blk
as 0, which incorrectly maps to a physical address of 0. This
occurs when block is 0 after the call to ocfs2_clusters_to_blocks
which is invoked inside the ocfs2_add_clusters_in_btree. The block
value is then passed to ocfs2_insert_extent, leading to the problem.

[1] https://syzkaller.appspot.com/bug?extid=18a87160c7d64ba2e2f6

Reported-and-tested-by: syzbot+18a87160c7d64ba2e2f6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=18a87160c7d64ba2e2f6
Signed-off-by: Mohammed Anees <pvmohammedanees2003@gmail.com>
---
 fs/ocfs2/alloc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
index 395e23920..926ffeed8 100644
--- a/fs/ocfs2/alloc.c
+++ b/fs/ocfs2/alloc.c
@@ -4843,6 +4843,13 @@ int ocfs2_add_clusters_in_btree(handle_t *handle,
 	}
 
 	block = ocfs2_clusters_to_blocks(osb->sb, bit_off);
+	if (block == 0) {
+		mlog(ML_ERROR, "Conversion resulted in zero block number");
+		status = -EIO;
+		need_free = 1;
+		goto bail;
+	}
+
 	trace_ocfs2_add_clusters_in_btree(
 	     (unsigned long long)ocfs2_metadata_cache_owner(et->et_ci),
 	     bit_off, num_bits);
-- 
2.46.0