From 63c9e47a1642fc817654a1bc18a6ec4bbcc0f056 Mon Sep 17 00:00:00 2001
From: "Steven J. Magnani" <magnani@ieee.org>
Date: Thu, 7 Jan 2021 17:41:16 -0600
Subject: [PATCH] udf: fix silent AED tagLocation corruption
Git-commit: 63c9e47a1642fc817654a1bc18a6ec4bbcc0f056
Patch-mainline: v5.12-rc1
References: bsc#1206645

When extending a file, udf_do_extend_file() may enter following empty
indirect extent. At the end of udf_do_extend_file() we revert prev_epos
to point to the last written extent. However if we end up not adding any
further extent in udf_do_extend_file(), the reverting points prev_epos
into the header area of the AED and following updates of the extents
(in udf_update_extents()) will corrupt the header.

Make sure that we do not follow indirect extent if we are not going to
add any more extents so that returning back to the last written extent
works correctly.

Link: https://lore.kernel.org/r/20210107234116.6190-2-magnani@ieee.org
Signed-off-by: Steven J. Magnani <magnani@ieee.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/udf/inode.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index bb89c3e43212..0dd2f93ac048 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -544,11 +544,14 @@ static int udf_do_extend_file(struct inode *inode,
 
 		udf_write_aext(inode, last_pos, &last_ext->extLocation,
 				last_ext->extLength, 1);
+
 		/*
-		 * We've rewritten the last extent but there may be empty
-		 * indirect extent after it - enter it.
+		 * We've rewritten the last extent. If we are going to add
+		 * more extents, we may need to enter possible following
+		 * empty indirect extent.
 		 */
-		udf_next_aext(inode, last_pos, &tmploc, &tmplen, 0);
+		if (new_block_bytes || prealloc_len)
+			udf_next_aext(inode, last_pos, &tmploc, &tmplen, 0);
 	}
 
 	/* Managed to do everything necessary? */
-- 
2.35.3