[3.8.y.z extended stable] Patch "ext4: don't try to modify s_flags if the the file system is read-only" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ext4: don't try to modify s_flags if the the file system is read-only

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.20.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 556f577f3573850fbf82f2f9c9649993d1e58186 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso at mit.edu>
Date: Wed, 12 Feb 2014 12:16:04 -0500
Subject: ext4: don't try to modify s_flags if the the file system is read-only

commit 23301410972330c0ae9a8afc379ba2005e249cc6 upstream.

If an ext4 file system is created by some tool other than mke2fs
(perhaps by someone who has a pathalogical fear of the GPL) that
doesn't set one or the other of the EXT2_FLAGS_{UN}SIGNED_HASH flags,
and that file system is then mounted read-only, don't try to modify
the s_flags field.  Otherwise, if dm_verity is in use, the superblock
will change, causing an dm_verity failure.

Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/ext4/super.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index c27683e..3e87d3a 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3578,16 +3578,22 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	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;
-	i = le32_to_cpu(es->s_flags);
-	if (i & EXT2_FLAGS_UNSIGNED_HASH)
-		sbi->s_hash_unsigned = 3;
-	else if ((i & EXT2_FLAGS_SIGNED_HASH) == 0) {
+	if (EXT4_HAS_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_DIR_INDEX)) {
+		i = le32_to_cpu(es->s_flags);
+		if (i & EXT2_FLAGS_UNSIGNED_HASH)
+			sbi->s_hash_unsigned = 3;
+		else if ((i & EXT2_FLAGS_SIGNED_HASH) == 0) {
 #ifdef __CHAR_UNSIGNED__
-		es->s_flags |= cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH);
-		sbi->s_hash_unsigned = 3;
+			if (!(sb->s_flags & MS_RDONLY))
+				es->s_flags |=
+					cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH);
+			sbi->s_hash_unsigned = 3;
 #else
-		es->s_flags |= cpu_to_le32(EXT2_FLAGS_SIGNED_HASH);
+			if (!(sb->s_flags & MS_RDONLY))
+				es->s_flags |=
+					cpu_to_le32(EXT2_FLAGS_SIGNED_HASH);
 #endif
+		}
 	}

 	/* Handle clustersize */
--
1.8.3.2