On Tue, Jun 04, 2024 at 03:06:32PM -0400, Gabriel Krisman Bertazi wrote:

Lizhi Xu [off-list ref] writes:

quoted

On Mon, 03 Jun 2024 10:50:51 -0400, Gabriel Krisman Bertazi wrote:

quoted

quoted

When mounting the ext4 filesystem, if the hash version and casefolded are not
consistent, exit the mounting.

Reported-by: syzbot+340581ba9dceb7e06fb3@syzkaller.appspotmail.com
Signed-off-by: Lizhi Xu <redacted>
---
 fs/ext4/super.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index c682fb927b64..0ad326504c50 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c

@@ -5262,6 +5262,11 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 		goto failed_mount;
 
 	ext4_hash_info_init(sb);
+	if (es->s_def_hash_version == DX_HASH_SIPHASH && 
+	    !ext4_has_feature_casefold(sb)) {

Can we ever have DX_HASH_SIPHASH set up in the super block?  I thought
it was used solely for directories where ext4_hash_in_dirent(inode) is
true.

The value of s'def_hash_version is obtained by reading the super block from the
buffer cache of the block device in ext4_load_super().

Yes, I know.  My point is whether this check should just be:

if (es->s_def_hash_version == DX_HASH_SIPHASH)
	goto failed_mount;

Since, IIUC, DX_HASH_SIPHASH is done per-directory and not written to
the sb.

That seems right to me.  SipHash can never be the default because it's only used
on directories that are both encrypted and casefolded.

- Eric