linux-kernel - [PATCH 6.6.y] ext4: fix error message when rejecting the default hash

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Message-ID: <20251215133957.4236-1-spyjetfayed@gmail.com>
Date: Mon, 15 Dec 2025 19:09:57 +0530
From: Ankan Biswas <spyjetfayed@...il.com>
To: stable@...r.kernel.org
Cc: gregkh@...uxfoundation.org,
	sashal@...nel.org,
	tytso@....edu,
	adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	skhan@...uxfoundation.org,
	khalid@...nel.org,
	david.hunter.linux@...il.com,
	linux-kernel-mentees@...r.kernel.org,
	Gabriel Krisman Bertazi <krisman@...e.de>,
	Ankan Biswas <spyjetfayed@...il.com>
Subject: [PATCH 6.6.y] ext4: fix error message when rejecting the default hash

From: Gabriel Krisman Bertazi <krisman@...e.de>

[ Upstream commit a2187431c395cdfbf144e3536f25468c64fc7cfa ]

Commit 985b67cd8639 ("ext4: filesystems without casefold feature cannot
be mounted with siphash") properly rejects volumes where
s_def_hash_version is set to DX_HASH_SIPHASH, but the check and the
error message should not look into casefold setup - a filesystem should
never have DX_HASH_SIPHASH as the default hash.  Fix it and, since we
are there, move the check to ext4_hash_info_init.

Fixes:985b67cd8639 ("ext4: filesystems without casefold feature cannot
be mounted with siphash")

Signed-off-by: Gabriel Krisman Bertazi <krisman@...e.de>
Link: https://patch.msgid.link/87jzg1en6j.fsf_-_@mailhost.krisman.be
Signed-off-by: Theodore Ts'o <tytso@....edu>
[ The commit a2187431c395 intended to remove the if-block which was used
  for an old SIPHASH rejection check. ]
Signed-off-by: Ankan Biswas <spyjetfayed@...il.com>
---
 fs/ext4/ext4.h  |  1 +
 fs/ext4/super.c | 20 +++++++++++++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 7afce7b744c0..85ba12a48f26 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2459,6 +2459,7 @@ static inline __le16 ext4_rec_len_to_disk(unsigned len, unsigned blocksize)
 #define DX_HASH_HALF_MD4_UNSIGNED	4
 #define DX_HASH_TEA_UNSIGNED		5
 #define DX_HASH_SIPHASH			6
+#define DX_HASH_LAST 			DX_HASH_SIPHASH
 
 static inline u32 ext4_chksum(struct ext4_sb_info *sbi, u32 crc,
 			      const void *address, unsigned int length)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 16a6c249580e..613f2bac439d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5138,16 +5138,27 @@ static int ext4_load_super(struct super_block *sb, ext4_fsblk_t *lsb,
 	return ret;
 }
 
-static void ext4_hash_info_init(struct super_block *sb)
+static int ext4_hash_info_init(struct super_block *sb)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct ext4_super_block *es = sbi->s_es;
 	unsigned int i;
 
+	sbi->s_def_hash_version = es->s_def_hash_version;
+
+	if (sbi->s_def_hash_version > DX_HASH_LAST) {
+		ext4_msg(sb, KERN_ERR,
+			 "Invalid default hash set in the superblock");
+		return -EINVAL;
+	} else if (sbi->s_def_hash_version == DX_HASH_SIPHASH) {
+		ext4_msg(sb, KERN_ERR,
+			 "SIPHASH is not a valid default hash value");
+		return -EINVAL;
+	}
+
 	for (i = 0; i < 4; i++)
 		sbi->s_hash_seed[i] = le32_to_cpu(es->s_hash_seed[i]);
 
-	sbi->s_def_hash_version = es->s_def_hash_version;
 	if (ext4_has_feature_dir_index(sb)) {
 		i = le32_to_cpu(es->s_flags);
 		if (i & EXT2_FLAGS_UNSIGNED_HASH)
@@ -5165,6 +5176,7 @@ static void ext4_hash_info_init(struct super_block *sb)
 #endif
 		}
 	}
+	return 0;
 }
 
 static int ext4_block_group_meta_init(struct super_block *sb, int silent)
@@ -5309,7 +5321,9 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 	if (err)
 		goto failed_mount;
 
-	ext4_hash_info_init(sb);
+	err = ext4_hash_info_init(sb);
+	if (err)
+		goto failed_mount;
 
 	err = ext4_handle_clustersize(sb);
 	if (err)
-- 
2.52.0