[PATCH][UBUNTU][SAUCE][SRU][B/F/G/H/I] ext4: fix directory index node split corruption

[Colin King]

From: Colin Ian King <colin.king at canonical.com>

BugLink: https://bugs.launchpad.net/bugs/1933074

[ Note: This was originally sent upstream to linux-ext4 at vger.kernel.org
  and Ted Tso but didn't seem to make it to the list, presumably as it
  was marked as SPAM

  See: http://www.voxelsoft.com/2021/ext4_large_dir_corruption.html ]

Following commit b5776e7, a trivial sequential write of empty files to
an empty ext4 file system (with large_dir enabled) fails after just
over 26 million files. Depending on luck, file creation will give error
EEXIST or EUCLEAN.

Commit b5776e7 fixed the no-restart condition so that
ext4_handle_dirty_dx_node is always called, but it also broke the
restart condition. This is because when restart=1, the original
implementation correctly skipped do_split() but b5776e7 clobbered the
"if(restart)goto journal_error;" logic.

This complementary change protects do_split() from restart condition,
making it safe from both current and future ordering of goto statements
in earlier sections of the code.

Tested on 5.11.20 with handy testing script:

i = 0
while i <= 32000000:
    print (i)
    with open('tmpmnt/%d' % i, 'wb') as fout:
        i += 1

Google-Bug-Id: 176345532
Fixes: b5776e7 ("ext4: fix potential htree index checksum corruption")
Fixes: e08ac99 ("ext4: add largedir feature")
Signed-off-by: denis at voxelsoft.com
Signed-off-by: Colin Ian King <colin.king at canonical.com>
---
 fs/ext4/namei.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 4c37abe..9ad5cc6 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2432,13 +2432,15 @@ static int ext4_dx_add_entry(handle_t *handle, struct ext4_filename *fname,
 			goto journal_error;
 		}
 	}
-	de = do_split(handle, dir, &bh, frame, &fname->hinfo);
-	if (IS_ERR(de)) {
-		err = PTR_ERR(de);
+	if (!restart) {
+		de = do_split(handle, dir, &bh, frame, &fname->hinfo);
+		if (IS_ERR(de)) {
+			err = PTR_ERR(de);
+			goto cleanup;
+		}
+		err = add_dirent_to_buf(handle, fname, dir, inode, de, bh);
 		goto cleanup;
 	}
-	err = add_dirent_to_buf(handle, fname, dir, inode, de, bh);
-	goto cleanup;
 
 journal_error:
 	ext4_std_error(dir->i_sb, err); /* this is a no-op if err == 0 */
-- 
2.7.4